LinuxTV Patchwork [Xen-devel,v5,1/1] cameraif: add ABI for para-virtual camera

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Submitter Oleksandr Andrushchenko
Date March 12, 2019, 8:20 a.m.
Message ID <20190312082000.32181-2-andr2000@gmail.com>
Download mbox | patch
Permalink /patch/55004/
State New
Delegated to: Hans Verkuil
Headers show

Comments

Oleksandr Andrushchenko - March 12, 2019, 8:20 a.m.
From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

This is the ABI for the two halves of a para-virtualized
camera driver which extends Xen's reach multimedia capabilities even
farther enabling it for video conferencing, In-Vehicle Infotainment,
high definition maps etc.

The initial goal is to support most needed functionality with the
final idea to make it possible to extend the protocol if need be:

1. Provide means for base virtual device configuration:
 - pixel formats
 - resolutions
 - frame rates
2. Support basic camera controls:
 - contrast
 - brightness
 - hue
 - saturation
3. Support streaming control

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
---
 xen/include/public/io/cameraif.h | 1370 ++++++++++++++++++++++++++++++
 1 file changed, 1370 insertions(+)
 create mode 100644 xen/include/public/io/cameraif.h
Juergen Gross - March 12, 2019, 8:38 a.m.
On 12/03/2019 09:20, Oleksandr Andrushchenko wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> 
> This is the ABI for the two halves of a para-virtualized
> camera driver which extends Xen's reach multimedia capabilities even
> farther enabling it for video conferencing, In-Vehicle Infotainment,
> high definition maps etc.
> 
> The initial goal is to support most needed functionality with the
> final idea to make it possible to extend the protocol if need be:
> 
> 1. Provide means for base virtual device configuration:
>  - pixel formats
>  - resolutions
>  - frame rates
> 2. Support basic camera controls:
>  - contrast
>  - brightness
>  - hue
>  - saturation
> 3. Support streaming control
> 
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen
Hans Verkuil - March 12, 2019, 8:58 a.m.
Hi Oleksandr,

Just one comment:

On 3/12/19 9:20 AM, Oleksandr Andrushchenko wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> 
> This is the ABI for the two halves of a para-virtualized
> camera driver which extends Xen's reach multimedia capabilities even
> farther enabling it for video conferencing, In-Vehicle Infotainment,
> high definition maps etc.
> 
> The initial goal is to support most needed functionality with the
> final idea to make it possible to extend the protocol if need be:
> 
> 1. Provide means for base virtual device configuration:
>  - pixel formats
>  - resolutions
>  - frame rates
> 2. Support basic camera controls:
>  - contrast
>  - brightness
>  - hue
>  - saturation
> 3. Support streaming control
> 
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> ---
>  xen/include/public/io/cameraif.h | 1370 ++++++++++++++++++++++++++++++
>  1 file changed, 1370 insertions(+)
>  create mode 100644 xen/include/public/io/cameraif.h
> 
> diff --git a/xen/include/public/io/cameraif.h b/xen/include/public/io/cameraif.h
> new file mode 100644
> index 000000000000..1ae4c51ea758
> --- /dev/null
> +++ b/xen/include/public/io/cameraif.h
> @@ -0,0 +1,1370 @@

<snip>

> +/*
> + * Request camera buffer's layout:
> + *         0                1                 2               3        octet
> + * +----------------+----------------+----------------+----------------+
> + * |               id                | _BUF_GET_LAYOUT|   reserved     | 4
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 8
> + * +----------------+----------------+----------------+----------------+
> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 64
> + * +----------------+----------------+----------------+----------------+
> + *
> + * See response format for this request.
> + *
> + *
> + * Request number of buffers to be used:
> + *         0                1                 2               3        octet
> + * +----------------+----------------+----------------+----------------+
> + * |               id                | _OP_BUF_REQUEST|   reserved     | 4
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 8
> + * +----------------+----------------+----------------+----------------+
> + * |    num_bufs    |                     reserved                     | 12
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 16
> + * +----------------+----------------+----------------+----------------+
> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 64
> + * +----------------+----------------+----------------+----------------+
> + *
> + * num_bufs - uint8_t, desired number of buffers to be used.
> + *
> + * If num_bufs is not zero then the backend validates the requested number of
> + * buffers and responds with the number of buffers allowed for this frontend.
> + * Frontend is responsible for checking the corresponding response in order to
> + * see if the values reported back by the backend do match the desired ones
> + * and can be accepted.
> + * Frontend is allowed to send multiple XENCAMERA_OP_BUF_REQUEST requests
> + * before sending XENCAMERA_OP_STREAM_START request to update or tune the
> + * final configuration.
> + * Frontend is not allowed to change the number of buffers and/or camera
> + * configuration after the streaming has started.

This last sentence isn't quite right, and I missed that when reviewing the
proposed text during the v4 discussions.

The bit about not being allowed to change the number of buffers when streaming
has started is correct.

But the camera configuration is more strict: you can't change the camera
configuration after this request unless you call this again with num_bufs = 0.

The camera configuration changes the buffer size, so once the buffers are
allocated you can no longer change the camera config. It is unrelated to streaming.

Regards,

	Hans

> + *
> + * If num_bufs is 0 and streaming has not started yet, then the backend will
> + * free all previously allocated buffers (if any).
> + * Trying to call this if streaming is in progress will result in an error.
> + *
> + * If camera reconfiguration is required then the streaming must be stopped
> + * and this request must be sent with num_bufs set to zero and finally
> + * buffers destroyed.
> + *
> + * Please note, that the number of buffers in this request must not exceed
> + * the value configured in XenStore.max-buffers.
> + *
> + * See response format for this request.
> + */

<snip>

Regards,

	Hans
Oleksandr Andrushchenko - March 12, 2019, 9:08 a.m.
On 3/12/19 10:58 AM, Hans Verkuil wrote:
> Hi Oleksandr,
>
> Just one comment:
>
> On 3/12/19 9:20 AM, Oleksandr Andrushchenko wrote:
>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>
>> This is the ABI for the two halves of a para-virtualized
>> camera driver which extends Xen's reach multimedia capabilities even
>> farther enabling it for video conferencing, In-Vehicle Infotainment,
>> high definition maps etc.
>>
>> The initial goal is to support most needed functionality with the
>> final idea to make it possible to extend the protocol if need be:
>>
>> 1. Provide means for base virtual device configuration:
>>   - pixel formats
>>   - resolutions
>>   - frame rates
>> 2. Support basic camera controls:
>>   - contrast
>>   - brightness
>>   - hue
>>   - saturation
>> 3. Support streaming control
>>
>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>> ---
>>   xen/include/public/io/cameraif.h | 1370 ++++++++++++++++++++++++++++++
>>   1 file changed, 1370 insertions(+)
>>   create mode 100644 xen/include/public/io/cameraif.h
>>
>> diff --git a/xen/include/public/io/cameraif.h b/xen/include/public/io/cameraif.h
>> new file mode 100644
>> index 000000000000..1ae4c51ea758
>> --- /dev/null
>> +++ b/xen/include/public/io/cameraif.h
>> @@ -0,0 +1,1370 @@
> <snip>
>
>> +/*
>> + * Request camera buffer's layout:
>> + *         0                1                 2               3        octet
>> + * +----------------+----------------+----------------+----------------+
>> + * |               id                | _BUF_GET_LAYOUT|   reserved     | 4
>> + * +----------------+----------------+----------------+----------------+
>> + * |                             reserved                              | 8
>> + * +----------------+----------------+----------------+----------------+
>> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
>> + * +----------------+----------------+----------------+----------------+
>> + * |                             reserved                              | 64
>> + * +----------------+----------------+----------------+----------------+
>> + *
>> + * See response format for this request.
>> + *
>> + *
>> + * Request number of buffers to be used:
>> + *         0                1                 2               3        octet
>> + * +----------------+----------------+----------------+----------------+
>> + * |               id                | _OP_BUF_REQUEST|   reserved     | 4
>> + * +----------------+----------------+----------------+----------------+
>> + * |                             reserved                              | 8
>> + * +----------------+----------------+----------------+----------------+
>> + * |    num_bufs    |                     reserved                     | 12
>> + * +----------------+----------------+----------------+----------------+
>> + * |                             reserved                              | 16
>> + * +----------------+----------------+----------------+----------------+
>> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
>> + * +----------------+----------------+----------------+----------------+
>> + * |                             reserved                              | 64
>> + * +----------------+----------------+----------------+----------------+
>> + *
>> + * num_bufs - uint8_t, desired number of buffers to be used.
>> + *
>> + * If num_bufs is not zero then the backend validates the requested number of
>> + * buffers and responds with the number of buffers allowed for this frontend.
>> + * Frontend is responsible for checking the corresponding response in order to
>> + * see if the values reported back by the backend do match the desired ones
>> + * and can be accepted.
>> + * Frontend is allowed to send multiple XENCAMERA_OP_BUF_REQUEST requests
>> + * before sending XENCAMERA_OP_STREAM_START request to update or tune the
>> + * final configuration.
>> + * Frontend is not allowed to change the number of buffers and/or camera
>> + * configuration after the streaming has started.
> This last sentence isn't quite right, and I missed that when reviewing the
> proposed text during the v4 discussions.
>
> The bit about not being allowed to change the number of buffers when streaming
> has started is correct.
>
> But the camera configuration is more strict: you can't change the camera
> configuration after this request unless you call this again with num_bufs = 0.
>
> The camera configuration changes the buffer size, so once the buffers are
> allocated you can no longer change the camera config. It is unrelated to streaming.
Can you please give me a hint of what would be the right thing to put in?

Thank you,
Oleksandr
> Regards,
>
> 	Hans
>
>> + *
>> + * If num_bufs is 0 and streaming has not started yet, then the backend will
>> + * free all previously allocated buffers (if any).
>> + * Trying to call this if streaming is in progress will result in an error.
>> + *
>> + * If camera reconfiguration is required then the streaming must be stopped
>> + * and this request must be sent with num_bufs set to zero and finally
>> + * buffers destroyed.
>> + *
>> + * Please note, that the number of buffers in this request must not exceed
>> + * the value configured in XenStore.max-buffers.
>> + *
>> + * See response format for this request.
>> + */
> <snip>
>
> Regards,
>
> 	Hans
Hans Verkuil - March 12, 2019, 9:30 a.m.
On 3/12/19 10:08 AM, Oleksandr Andrushchenko wrote:
> On 3/12/19 10:58 AM, Hans Verkuil wrote:
>> Hi Oleksandr,
>>
>> Just one comment:
>>
>> On 3/12/19 9:20 AM, Oleksandr Andrushchenko wrote:
>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>
>>> This is the ABI for the two halves of a para-virtualized
>>> camera driver which extends Xen's reach multimedia capabilities even
>>> farther enabling it for video conferencing, In-Vehicle Infotainment,
>>> high definition maps etc.
>>>
>>> The initial goal is to support most needed functionality with the
>>> final idea to make it possible to extend the protocol if need be:
>>>
>>> 1. Provide means for base virtual device configuration:
>>>   - pixel formats
>>>   - resolutions
>>>   - frame rates
>>> 2. Support basic camera controls:
>>>   - contrast
>>>   - brightness
>>>   - hue
>>>   - saturation
>>> 3. Support streaming control
>>>
>>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>> ---
>>>   xen/include/public/io/cameraif.h | 1370 ++++++++++++++++++++++++++++++
>>>   1 file changed, 1370 insertions(+)
>>>   create mode 100644 xen/include/public/io/cameraif.h
>>>
>>> diff --git a/xen/include/public/io/cameraif.h b/xen/include/public/io/cameraif.h
>>> new file mode 100644
>>> index 000000000000..1ae4c51ea758
>>> --- /dev/null
>>> +++ b/xen/include/public/io/cameraif.h
>>> @@ -0,0 +1,1370 @@
>> <snip>
>>
>>> +/*
>>> + * Request camera buffer's layout:
>>> + *         0                1                 2               3        octet
>>> + * +----------------+----------------+----------------+----------------+
>>> + * |               id                | _BUF_GET_LAYOUT|   reserved     | 4
>>> + * +----------------+----------------+----------------+----------------+
>>> + * |                             reserved                              | 8
>>> + * +----------------+----------------+----------------+----------------+
>>> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
>>> + * +----------------+----------------+----------------+----------------+
>>> + * |                             reserved                              | 64
>>> + * +----------------+----------------+----------------+----------------+
>>> + *
>>> + * See response format for this request.
>>> + *
>>> + *
>>> + * Request number of buffers to be used:
>>> + *         0                1                 2               3        octet
>>> + * +----------------+----------------+----------------+----------------+
>>> + * |               id                | _OP_BUF_REQUEST|   reserved     | 4
>>> + * +----------------+----------------+----------------+----------------+
>>> + * |                             reserved                              | 8
>>> + * +----------------+----------------+----------------+----------------+
>>> + * |    num_bufs    |                     reserved                     | 12
>>> + * +----------------+----------------+----------------+----------------+
>>> + * |                             reserved                              | 16
>>> + * +----------------+----------------+----------------+----------------+
>>> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
>>> + * +----------------+----------------+----------------+----------------+
>>> + * |                             reserved                              | 64
>>> + * +----------------+----------------+----------------+----------------+
>>> + *
>>> + * num_bufs - uint8_t, desired number of buffers to be used.
>>> + *
>>> + * If num_bufs is not zero then the backend validates the requested number of
>>> + * buffers and responds with the number of buffers allowed for this frontend.
>>> + * Frontend is responsible for checking the corresponding response in order to
>>> + * see if the values reported back by the backend do match the desired ones
>>> + * and can be accepted.
>>> + * Frontend is allowed to send multiple XENCAMERA_OP_BUF_REQUEST requests
>>> + * before sending XENCAMERA_OP_STREAM_START request to update or tune the
>>> + * final configuration.
>>> + * Frontend is not allowed to change the number of buffers and/or camera
>>> + * configuration after the streaming has started.
>> This last sentence isn't quite right, and I missed that when reviewing the
>> proposed text during the v4 discussions.
>>
>> The bit about not being allowed to change the number of buffers when streaming
>> has started is correct.
>>
>> But the camera configuration is more strict: you can't change the camera
>> configuration after this request unless you call this again with num_bufs = 0.
>>
>> The camera configuration changes the buffer size, so once the buffers are
>> allocated you can no longer change the camera config. It is unrelated to streaming.
> Can you please give me a hint of what would be the right thing to put in?

How about this:

Frontend is not allowed to change the camera configuration after this call with
a non-zero value of num_bufs. If camera reconfiguration is required then this
request must be sent with num_bufs set to zero and any created buffers must be
destroyed first.

Frontend is not allowed to change the number of buffers after the streaming has started.


> 
> Thank you,
> Oleksandr
>> Regards,
>>
>> 	Hans
>>
>>> + *
>>> + * If num_bufs is 0 and streaming has not started yet, then the backend will
>>> + * free all previously allocated buffers (if any).
>>> + * Trying to call this if streaming is in progress will result in an error.
>>> + *
>>> + * If camera reconfiguration is required then the streaming must be stopped
>>> + * and this request must be sent with num_bufs set to zero and finally
>>> + * buffers destroyed.

I would rewrite the last part as well:

...set to zero and any created buffers must be destroyed.


Note that "any created buffers must be destroyed" is something that you need to
check for in your code if I am not mistaken.

Regards,

	Hans

>>> + *
>>> + * Please note, that the number of buffers in this request must not exceed
>>> + * the value configured in XenStore.max-buffers.
>>> + *
>>> + * See response format for this request.
>>> + */
>> <snip>
>>
>> Regards,
>>
>> 	Hans
>
Oleksandr Andrushchenko - March 12, 2019, 9:35 a.m.
On 3/12/19 11:30 AM, Hans Verkuil wrote:
> On 3/12/19 10:08 AM, Oleksandr Andrushchenko wrote:
>> On 3/12/19 10:58 AM, Hans Verkuil wrote:
>>> Hi Oleksandr,
>>>
>>> Just one comment:
>>>
>>> On 3/12/19 9:20 AM, Oleksandr Andrushchenko wrote:
>>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>>
>>>> This is the ABI for the two halves of a para-virtualized
>>>> camera driver which extends Xen's reach multimedia capabilities even
>>>> farther enabling it for video conferencing, In-Vehicle Infotainment,
>>>> high definition maps etc.
>>>>
>>>> The initial goal is to support most needed functionality with the
>>>> final idea to make it possible to extend the protocol if need be:
>>>>
>>>> 1. Provide means for base virtual device configuration:
>>>>    - pixel formats
>>>>    - resolutions
>>>>    - frame rates
>>>> 2. Support basic camera controls:
>>>>    - contrast
>>>>    - brightness
>>>>    - hue
>>>>    - saturation
>>>> 3. Support streaming control
>>>>
>>>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>> ---
>>>>    xen/include/public/io/cameraif.h | 1370 ++++++++++++++++++++++++++++++
>>>>    1 file changed, 1370 insertions(+)
>>>>    create mode 100644 xen/include/public/io/cameraif.h
>>>>
>>>> diff --git a/xen/include/public/io/cameraif.h b/xen/include/public/io/cameraif.h
>>>> new file mode 100644
>>>> index 000000000000..1ae4c51ea758
>>>> --- /dev/null
>>>> +++ b/xen/include/public/io/cameraif.h
>>>> @@ -0,0 +1,1370 @@
>>> <snip>
>>>
>>>> +/*
>>>> + * Request camera buffer's layout:
>>>> + *         0                1                 2               3        octet
>>>> + * +----------------+----------------+----------------+----------------+
>>>> + * |               id                | _BUF_GET_LAYOUT|   reserved     | 4
>>>> + * +----------------+----------------+----------------+----------------+
>>>> + * |                             reserved                              | 8
>>>> + * +----------------+----------------+----------------+----------------+
>>>> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
>>>> + * +----------------+----------------+----------------+----------------+
>>>> + * |                             reserved                              | 64
>>>> + * +----------------+----------------+----------------+----------------+
>>>> + *
>>>> + * See response format for this request.
>>>> + *
>>>> + *
>>>> + * Request number of buffers to be used:
>>>> + *         0                1                 2               3        octet
>>>> + * +----------------+----------------+----------------+----------------+
>>>> + * |               id                | _OP_BUF_REQUEST|   reserved     | 4
>>>> + * +----------------+----------------+----------------+----------------+
>>>> + * |                             reserved                              | 8
>>>> + * +----------------+----------------+----------------+----------------+
>>>> + * |    num_bufs    |                     reserved                     | 12
>>>> + * +----------------+----------------+----------------+----------------+
>>>> + * |                             reserved                              | 16
>>>> + * +----------------+----------------+----------------+----------------+
>>>> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
>>>> + * +----------------+----------------+----------------+----------------+
>>>> + * |                             reserved                              | 64
>>>> + * +----------------+----------------+----------------+----------------+
>>>> + *
>>>> + * num_bufs - uint8_t, desired number of buffers to be used.
>>>> + *
>>>> + * If num_bufs is not zero then the backend validates the requested number of
>>>> + * buffers and responds with the number of buffers allowed for this frontend.
>>>> + * Frontend is responsible for checking the corresponding response in order to
>>>> + * see if the values reported back by the backend do match the desired ones
>>>> + * and can be accepted.
>>>> + * Frontend is allowed to send multiple XENCAMERA_OP_BUF_REQUEST requests
>>>> + * before sending XENCAMERA_OP_STREAM_START request to update or tune the
>>>> + * final configuration.
>>>> + * Frontend is not allowed to change the number of buffers and/or camera
>>>> + * configuration after the streaming has started.
>>> This last sentence isn't quite right, and I missed that when reviewing the
>>> proposed text during the v4 discussions.
>>>
>>> The bit about not being allowed to change the number of buffers when streaming
>>> has started is correct.
>>>
>>> But the camera configuration is more strict: you can't change the camera
>>> configuration after this request unless you call this again with num_bufs = 0.
>>>
>>> The camera configuration changes the buffer size, so once the buffers are
>>> allocated you can no longer change the camera config. It is unrelated to streaming.
>> Can you please give me a hint of what would be the right thing to put in?
> How about this:
>
> Frontend is not allowed to change the camera configuration after this call with
> a non-zero value of num_bufs. If camera reconfiguration is required then this
> request must be sent with num_bufs set to zero and any created buffers must be
> destroyed first.
>
> Frontend is not allowed to change the number of buffers after the streaming has started.
Sounds great, so I'll replace:

"Frontend is not allowed to change the number of buffers and/or camera
  configuration after the streaming has started."

with:

"Frontend is not allowed to change the camera configuration after this 
call with
  a non-zero value of num_bufs. If camera reconfiguration is required 
then this
  request must be sent with num_bufs set to zero and any created buffers 
must be
  destroyed first.

  Frontend is not allowed to change the number of buffers after the 
streaming has started.
"

Are these all the changes you see at the moment?

Thank you!
>
>> Thank you,
>> Oleksandr
>>> Regards,
>>>
>>> 	Hans
>>>
>>>> + *
>>>> + * If num_bufs is 0 and streaming has not started yet, then the backend will
>>>> + * free all previously allocated buffers (if any).
>>>> + * Trying to call this if streaming is in progress will result in an error.
>>>> + *
>>>> + * If camera reconfiguration is required then the streaming must be stopped
>>>> + * and this request must be sent with num_bufs set to zero and finally
>>>> + * buffers destroyed.
> I would rewrite the last part as well:
>
> ...set to zero and any created buffers must be destroyed.
>
>
> Note that "any created buffers must be destroyed" is something that you need to
> check for in your code if I am not mistaken.
>
> Regards,
>
> 	Hans
>
>>>> + *
>>>> + * Please note, that the number of buffers in this request must not exceed
>>>> + * the value configured in XenStore.max-buffers.
>>>> + *
>>>> + * See response format for this request.
>>>> + */
>>> <snip>
>>>
>>> Regards,
>>>
>>> 	Hans
Hans Verkuil - March 12, 2019, 10:09 a.m.
On 3/12/19 10:35 AM, Oleksandr Andrushchenko wrote:
> On 3/12/19 11:30 AM, Hans Verkuil wrote:
>> On 3/12/19 10:08 AM, Oleksandr Andrushchenko wrote:
>>> On 3/12/19 10:58 AM, Hans Verkuil wrote:
>>>> Hi Oleksandr,
>>>>
>>>> Just one comment:
>>>>
>>>> On 3/12/19 9:20 AM, Oleksandr Andrushchenko wrote:
>>>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>>>
>>>>> This is the ABI for the two halves of a para-virtualized
>>>>> camera driver which extends Xen's reach multimedia capabilities even
>>>>> farther enabling it for video conferencing, In-Vehicle Infotainment,
>>>>> high definition maps etc.
>>>>>
>>>>> The initial goal is to support most needed functionality with the
>>>>> final idea to make it possible to extend the protocol if need be:
>>>>>
>>>>> 1. Provide means for base virtual device configuration:
>>>>>    - pixel formats
>>>>>    - resolutions
>>>>>    - frame rates
>>>>> 2. Support basic camera controls:
>>>>>    - contrast
>>>>>    - brightness
>>>>>    - hue
>>>>>    - saturation
>>>>> 3. Support streaming control
>>>>>
>>>>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>>> ---
>>>>>    xen/include/public/io/cameraif.h | 1370 ++++++++++++++++++++++++++++++
>>>>>    1 file changed, 1370 insertions(+)
>>>>>    create mode 100644 xen/include/public/io/cameraif.h
>>>>>
>>>>> diff --git a/xen/include/public/io/cameraif.h b/xen/include/public/io/cameraif.h
>>>>> new file mode 100644
>>>>> index 000000000000..1ae4c51ea758
>>>>> --- /dev/null
>>>>> +++ b/xen/include/public/io/cameraif.h
>>>>> @@ -0,0 +1,1370 @@
>>>> <snip>
>>>>
>>>>> +/*
>>>>> + * Request camera buffer's layout:
>>>>> + *         0                1                 2               3        octet
>>>>> + * +----------------+----------------+----------------+----------------+
>>>>> + * |               id                | _BUF_GET_LAYOUT|   reserved     | 4
>>>>> + * +----------------+----------------+----------------+----------------+
>>>>> + * |                             reserved                              | 8
>>>>> + * +----------------+----------------+----------------+----------------+
>>>>> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
>>>>> + * +----------------+----------------+----------------+----------------+
>>>>> + * |                             reserved                              | 64
>>>>> + * +----------------+----------------+----------------+----------------+
>>>>> + *
>>>>> + * See response format for this request.
>>>>> + *
>>>>> + *
>>>>> + * Request number of buffers to be used:
>>>>> + *         0                1                 2               3        octet
>>>>> + * +----------------+----------------+----------------+----------------+
>>>>> + * |               id                | _OP_BUF_REQUEST|   reserved     | 4
>>>>> + * +----------------+----------------+----------------+----------------+
>>>>> + * |                             reserved                              | 8
>>>>> + * +----------------+----------------+----------------+----------------+
>>>>> + * |    num_bufs    |                     reserved                     | 12
>>>>> + * +----------------+----------------+----------------+----------------+
>>>>> + * |                             reserved                              | 16
>>>>> + * +----------------+----------------+----------------+----------------+
>>>>> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
>>>>> + * +----------------+----------------+----------------+----------------+
>>>>> + * |                             reserved                              | 64
>>>>> + * +----------------+----------------+----------------+----------------+
>>>>> + *
>>>>> + * num_bufs - uint8_t, desired number of buffers to be used.
>>>>> + *
>>>>> + * If num_bufs is not zero then the backend validates the requested number of
>>>>> + * buffers and responds with the number of buffers allowed for this frontend.
>>>>> + * Frontend is responsible for checking the corresponding response in order to
>>>>> + * see if the values reported back by the backend do match the desired ones
>>>>> + * and can be accepted.
>>>>> + * Frontend is allowed to send multiple XENCAMERA_OP_BUF_REQUEST requests
>>>>> + * before sending XENCAMERA_OP_STREAM_START request to update or tune the
>>>>> + * final configuration.
>>>>> + * Frontend is not allowed to change the number of buffers and/or camera
>>>>> + * configuration after the streaming has started.
>>>> This last sentence isn't quite right, and I missed that when reviewing the
>>>> proposed text during the v4 discussions.
>>>>
>>>> The bit about not being allowed to change the number of buffers when streaming
>>>> has started is correct.
>>>>
>>>> But the camera configuration is more strict: you can't change the camera
>>>> configuration after this request unless you call this again with num_bufs = 0.
>>>>
>>>> The camera configuration changes the buffer size, so once the buffers are
>>>> allocated you can no longer change the camera config. It is unrelated to streaming.
>>> Can you please give me a hint of what would be the right thing to put in?
>> How about this:
>>
>> Frontend is not allowed to change the camera configuration after this call with
>> a non-zero value of num_bufs. If camera reconfiguration is required then this
>> request must be sent with num_bufs set to zero and any created buffers must be
>> destroyed first.
>>
>> Frontend is not allowed to change the number of buffers after the streaming has started.
> Sounds great, so I'll replace:
> 
> "Frontend is not allowed to change the number of buffers and/or camera
>   configuration after the streaming has started."
> 
> with:
> 
> "Frontend is not allowed to change the camera configuration after this 
> call with
>   a non-zero value of num_bufs. If camera reconfiguration is required 
> then this
>   request must be sent with num_bufs set to zero and any created buffers 
> must be
>   destroyed first.
> 
>   Frontend is not allowed to change the number of buffers after the 
> streaming has started.
> "
> 
> Are these all the changes you see at the moment?

Also this change below...

>>>>> + *
>>>>> + * If num_bufs is 0 and streaming has not started yet, then the backend will
>>>>> + * free all previously allocated buffers (if any).
>>>>> + * Trying to call this if streaming is in progress will result in an error.
>>>>> + *
>>>>> + * If camera reconfiguration is required then the streaming must be stopped
>>>>> + * and this request must be sent with num_bufs set to zero and finally
>>>>> + * buffers destroyed.
>> I would rewrite the last part as well:
>>
>> ...set to zero and any created buffers must be destroyed.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

And note my note below :-)

>>
>>
>> Note that "any created buffers must be destroyed" is something that you need to
>> check for in your code if I am not mistaken.

^^^^^^^^^^^^^^^^^

Regards,

	Hans
Oleksandr Andrushchenko - March 12, 2019, 10:11 a.m.
On 3/12/19 12:09 PM, Hans Verkuil wrote:
> On 3/12/19 10:35 AM, Oleksandr Andrushchenko wrote:
>> On 3/12/19 11:30 AM, Hans Verkuil wrote:
>>> On 3/12/19 10:08 AM, Oleksandr Andrushchenko wrote:
>>>> On 3/12/19 10:58 AM, Hans Verkuil wrote:
>>>>> Hi Oleksandr,
>>>>>
>>>>> Just one comment:
>>>>>
>>>>> On 3/12/19 9:20 AM, Oleksandr Andrushchenko wrote:
>>>>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>>>>
>>>>>> This is the ABI for the two halves of a para-virtualized
>>>>>> camera driver which extends Xen's reach multimedia capabilities even
>>>>>> farther enabling it for video conferencing, In-Vehicle Infotainment,
>>>>>> high definition maps etc.
>>>>>>
>>>>>> The initial goal is to support most needed functionality with the
>>>>>> final idea to make it possible to extend the protocol if need be:
>>>>>>
>>>>>> 1. Provide means for base virtual device configuration:
>>>>>>     - pixel formats
>>>>>>     - resolutions
>>>>>>     - frame rates
>>>>>> 2. Support basic camera controls:
>>>>>>     - contrast
>>>>>>     - brightness
>>>>>>     - hue
>>>>>>     - saturation
>>>>>> 3. Support streaming control
>>>>>>
>>>>>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>>>> ---
>>>>>>     xen/include/public/io/cameraif.h | 1370 ++++++++++++++++++++++++++++++
>>>>>>     1 file changed, 1370 insertions(+)
>>>>>>     create mode 100644 xen/include/public/io/cameraif.h
>>>>>>
>>>>>> diff --git a/xen/include/public/io/cameraif.h b/xen/include/public/io/cameraif.h
>>>>>> new file mode 100644
>>>>>> index 000000000000..1ae4c51ea758
>>>>>> --- /dev/null
>>>>>> +++ b/xen/include/public/io/cameraif.h
>>>>>> @@ -0,0 +1,1370 @@
>>>>> <snip>
>>>>>
>>>>>> +/*
>>>>>> + * Request camera buffer's layout:
>>>>>> + *         0                1                 2               3        octet
>>>>>> + * +----------------+----------------+----------------+----------------+
>>>>>> + * |               id                | _BUF_GET_LAYOUT|   reserved     | 4
>>>>>> + * +----------------+----------------+----------------+----------------+
>>>>>> + * |                             reserved                              | 8
>>>>>> + * +----------------+----------------+----------------+----------------+
>>>>>> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
>>>>>> + * +----------------+----------------+----------------+----------------+
>>>>>> + * |                             reserved                              | 64
>>>>>> + * +----------------+----------------+----------------+----------------+
>>>>>> + *
>>>>>> + * See response format for this request.
>>>>>> + *
>>>>>> + *
>>>>>> + * Request number of buffers to be used:
>>>>>> + *         0                1                 2               3        octet
>>>>>> + * +----------------+----------------+----------------+----------------+
>>>>>> + * |               id                | _OP_BUF_REQUEST|   reserved     | 4
>>>>>> + * +----------------+----------------+----------------+----------------+
>>>>>> + * |                             reserved                              | 8
>>>>>> + * +----------------+----------------+----------------+----------------+
>>>>>> + * |    num_bufs    |                     reserved                     | 12
>>>>>> + * +----------------+----------------+----------------+----------------+
>>>>>> + * |                             reserved                              | 16
>>>>>> + * +----------------+----------------+----------------+----------------+
>>>>>> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
>>>>>> + * +----------------+----------------+----------------+----------------+
>>>>>> + * |                             reserved                              | 64
>>>>>> + * +----------------+----------------+----------------+----------------+
>>>>>> + *
>>>>>> + * num_bufs - uint8_t, desired number of buffers to be used.
>>>>>> + *
>>>>>> + * If num_bufs is not zero then the backend validates the requested number of
>>>>>> + * buffers and responds with the number of buffers allowed for this frontend.
>>>>>> + * Frontend is responsible for checking the corresponding response in order to
>>>>>> + * see if the values reported back by the backend do match the desired ones
>>>>>> + * and can be accepted.
>>>>>> + * Frontend is allowed to send multiple XENCAMERA_OP_BUF_REQUEST requests
>>>>>> + * before sending XENCAMERA_OP_STREAM_START request to update or tune the
>>>>>> + * final configuration.
>>>>>> + * Frontend is not allowed to change the number of buffers and/or camera
>>>>>> + * configuration after the streaming has started.
>>>>> This last sentence isn't quite right, and I missed that when reviewing the
>>>>> proposed text during the v4 discussions.
>>>>>
>>>>> The bit about not being allowed to change the number of buffers when streaming
>>>>> has started is correct.
>>>>>
>>>>> But the camera configuration is more strict: you can't change the camera
>>>>> configuration after this request unless you call this again with num_bufs = 0.
>>>>>
>>>>> The camera configuration changes the buffer size, so once the buffers are
>>>>> allocated you can no longer change the camera config. It is unrelated to streaming.
>>>> Can you please give me a hint of what would be the right thing to put in?
>>> How about this:
>>>
>>> Frontend is not allowed to change the camera configuration after this call with
>>> a non-zero value of num_bufs. If camera reconfiguration is required then this
>>> request must be sent with num_bufs set to zero and any created buffers must be
>>> destroyed first.
>>>
>>> Frontend is not allowed to change the number of buffers after the streaming has started.
>> Sounds great, so I'll replace:
>>
>> "Frontend is not allowed to change the number of buffers and/or camera
>>    configuration after the streaming has started."
>>
>> with:
>>
>> "Frontend is not allowed to change the camera configuration after this
>> call with
>>    a non-zero value of num_bufs. If camera reconfiguration is required
>> then this
>>    request must be sent with num_bufs set to zero and any created buffers
>> must be
>>    destroyed first.
>>
>>    Frontend is not allowed to change the number of buffers after the
>> streaming has started.
>> "
>>
>> Are these all the changes you see at the moment?
> Also this change below...
>
>>>>>> + *
>>>>>> + * If num_bufs is 0 and streaming has not started yet, then the backend will
>>>>>> + * free all previously allocated buffers (if any).
>>>>>> + * Trying to call this if streaming is in progress will result in an error.
>>>>>> + *
>>>>>> + * If camera reconfiguration is required then the streaming must be stopped
>>>>>> + * and this request must be sent with num_bufs set to zero and finally
>>>>>> + * buffers destroyed.
>>> I would rewrite the last part as well:
>>>
>>> ...set to zero and any created buffers must be destroyed.
Ah, indeed I missed this one ;)
Thank you
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> And note my note below :-)
>
>>>
>>> Note that "any created buffers must be destroyed" is something that you need to
>>> check for in your code if I am not mistaken.
Yes, thank you
> ^^^^^^^^^^^^^^^^^
>
> Regards,
>
> 	Hans
Oleksandr Andrushchenko - March 13, 2019, 8:46 a.m.
On 3/12/19 10:38 AM, Juergen Gross wrote:
> On 12/03/2019 09:20, Oleksandr Andrushchenko wrote:
>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>
>> This is the ABI for the two halves of a para-virtualized
>> camera driver which extends Xen's reach multimedia capabilities even
>> farther enabling it for video conferencing, In-Vehicle Infotainment,
>> high definition maps etc.
>>
>> The initial goal is to support most needed functionality with the
>> final idea to make it possible to extend the protocol if need be:
>>
>> 1. Provide means for base virtual device configuration:
>>   - pixel formats
>>   - resolutions
>>   - frame rates
>> 2. Support basic camera controls:
>>   - contrast
>>   - brightness
>>   - hue
>>   - saturation
>> 3. Support streaming control
>>
>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> Reviewed-by: Juergen Gross <jgross@suse.com>
Thank you,
I'll wait till the next week for any other comments and if there
are only those from Hans then I'll push (final?) v6
>
> Juergen
Thank you,
Oleksandr

Patch

diff --git a/xen/include/public/io/cameraif.h b/xen/include/public/io/cameraif.h
new file mode 100644
index 000000000000..1ae4c51ea758
--- /dev/null
+++ b/xen/include/public/io/cameraif.h
@@ -0,0 +1,1370 @@ 
+/******************************************************************************
+ * cameraif.h
+ *
+ * Unified camera device I/O interface for Xen guest OSes.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ *
+ * Copyright (C) 2018-2019 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
+ */
+
+#ifndef __XEN_PUBLIC_IO_CAMERAIF_H__
+#define __XEN_PUBLIC_IO_CAMERAIF_H__
+
+#include "ring.h"
+#include "../grant_table.h"
+
+/*
+ ******************************************************************************
+ *                           Protocol version
+ ******************************************************************************
+ */
+#define XENCAMERA_PROTOCOL_VERSION     "1"
+
+/*
+ ******************************************************************************
+ *                  Feature and Parameter Negotiation
+ ******************************************************************************
+ *
+ * Front->back notifications: when enqueuing a new request, sending a
+ * notification can be made conditional on xencamera_req (i.e., the generic
+ * hold-off mechanism provided by the ring macros). Backends must set
+ * xencamera_req appropriately (e.g., using RING_FINAL_CHECK_FOR_REQUESTS()).
+ *
+ * Back->front notifications: when enqueuing a new response, sending a
+ * notification can be made conditional on xencamera_resp (i.e., the generic
+ * hold-off mechanism provided by the ring macros). Frontends must set
+ * xencamera_resp appropriately (e.g., using RING_FINAL_CHECK_FOR_RESPONSES()).
+ *
+ * The two halves of a para-virtual camera driver utilize nodes within
+ * XenStore to communicate capabilities and to negotiate operating parameters.
+ * This section enumerates these nodes which reside in the respective front and
+ * backend portions of XenStore, following the XenBus convention.
+ *
+ * All data in XenStore is stored as strings. Nodes specifying numeric
+ * values are encoded in decimal. Integer value ranges listed below are
+ * expressed as fixed sized integer types capable of storing the conversion
+ * of a properly formatted node string, without loss of information.
+ *
+ ******************************************************************************
+ *                        Example configuration
+ ******************************************************************************
+ *
+ * This is an example of backend and frontend configuration:
+ *
+ *--------------------------------- Backend -----------------------------------
+ *
+ * /local/domain/0/backend/vcamera/1/0/frontend-id = "1"
+ * /local/domain/0/backend/vcamera/1/0/frontend = "/local/domain/1/device/vcamera/0"
+ * /local/domain/0/backend/vcamera/1/0/state = "4"
+ * /local/domain/0/backend/vcamera/1/0/versions = "1,2"
+ *
+ *--------------------------------- Frontend ----------------------------------
+ *
+ * /local/domain/1/device/vcamera/0/backend-id = "0"
+ * /local/domain/1/device/vcamera/0/backend = "/local/domain/0/backend/vcamera/1"
+ * /local/domain/1/device/vcamera/0/state = "4"
+ * /local/domain/1/device/vcamera/0/version = "1"
+ * /local/domain/1/device/vcamera/0/be-alloc = "1"
+ *
+ *---------------------------- Device 0 configuration -------------------------
+ *
+ * /local/domain/1/device/vcamera/0/max-buffers = "3"
+ * /local/domain/1/device/vcamera/0/controls = "contrast,hue"
+ * /local/domain/1/device/vcamera/0/formats/YUYV/640x480/frame-rates = "30/1,15/1"
+ * /local/domain/1/device/vcamera/0/formats/YUYV/1920x1080/frame-rates = "15/2"
+ * /local/domain/1/device/vcamera/0/formats/BGRA/640x480/frame-rates = "15/1,15/2"
+ * /local/domain/1/device/vcamera/0/formats/BGRA/1200x720/frame-rates = "15/2"
+ * /local/domain/1/device/vcamera/0/unique-id = "0"
+ * /local/domain/1/device/vcamera/0/req-ring-ref = "2832"
+ * /local/domain/1/device/vcamera/0/req-event-channel = "15"
+ * /local/domain/1/device/vcamera/0/evt-ring-ref = "387"
+ * /local/domain/1/device/vcamera/0/evt-event-channel = "16"
+ *
+ *---------------------------- Device 1 configuration -------------------------
+ *
+ * /local/domain/1/device/vcamera/1/max-buffers = "8"
+ * /local/domain/1/device/vcamera/1/controls = "brightness,saturation,hue"
+ * /local/domain/1/device/vcamera/1/formats/YUYV/640x480/frame-rates = "30/1,15/2"
+ * /local/domain/1/device/vcamera/1/formats/YUYV/1920x1080/frame-rates = "15/2"
+ * /local/domain/1/device/vcamera/1/unique-id = "1"
+ * /local/domain/1/device/vcamera/1/req-ring-ref = "2833"
+ * /local/domain/1/device/vcamera/1/req-event-channel = "17"
+ * /local/domain/1/device/vcamera/1/evt-ring-ref = "388"
+ * /local/domain/1/device/vcamera/1/evt-event-channel = "18"
+ *
+ ******************************************************************************
+ *                            Backend XenBus Nodes
+ ******************************************************************************
+ *
+ *----------------------------- Protocol version ------------------------------
+ *
+ * versions
+ *      Values:         <string>
+ *
+ *      List of XENCAMERA_LIST_SEPARATOR separated protocol versions supported
+ *      by the backend. For example "1,2,3".
+ *
+ ******************************************************************************
+ *                            Frontend XenBus Nodes
+ ******************************************************************************
+ *
+ *-------------------------------- Addressing ---------------------------------
+ *
+ * dom-id
+ *      Values:         <uint16_t>
+ *
+ *      Domain identifier.
+ *
+ * dev-id
+ *      Values:         <uint16_t>
+ *
+ *      Device identifier.
+ *
+ *      /local/domain/<dom-id>/device/vcamera/<dev-id>/...
+ *
+ *----------------------------- Protocol version ------------------------------
+ *
+ * version
+ *      Values:         <string>
+ *
+ *      Protocol version, chosen among the ones supported by the backend.
+ *
+ *------------------------- Backend buffer allocation -------------------------
+ *
+ * be-alloc
+ *      Values:         "0", "1"
+ *
+ *      If value is set to "1", then backend will be the buffer
+ *      provider/allocator for this domain during XENCAMERA_OP_BUF_CREATE
+ *      operation.
+ *      If value is not "1" or omitted frontend must allocate buffers itself.
+ *
+ *------------------------------- Camera settings -----------------------------
+ *
+ * unique-id
+ *      Values:         <string>
+ *
+ *      After device instance initialization each camera is assigned a
+ *      unique ID, so it can be identified by the backend by this ID.
+ *      This can be UUID or such.
+ *
+ * max-buffers
+ *      Values:         <uint8_t>
+ *
+ *      Maximum number of camera buffers this frontend may use.
+ *
+ * controls
+ *      Values:         <list of string>
+ *
+ *      List of supported camera controls separated by XENCAMERA_LIST_SEPARATOR.
+ *      Camera controls are expressed as a list of string values w/o any
+ *      ordering requirement.
+ *
+ * formats
+ *      Values:         <format, char[7]>
+ *
+ *      Formats are organized as a set of directories one per each
+ *      supported pixel format. The name of the directory is the
+ *      corresponding FOURCC string label. The next level of
+ *      the directory under <formats> represents supported resolutions.
+ *      If the format represents a big-endian variant of a little
+ *      endian format, then the "-BE" suffix must be added. E.g. 'AR15' vs
+ *      'AR15-BE'.
+ *      If FOURCC string label has spaces then those are only allowed to
+ *      be at the end of the label and must be trimmed, for example
+ *      'Y16' and 'Y16-BE' will be trimmed.
+ *
+ * resolution
+ *      Values:         <width, uint32_t>x<height, uint32_t>
+ *
+ *      Resolutions are organized as a set of directories one per each
+ *      supported resolution under corresponding <formats> directory.
+ *      The name of the directory is the supported width and height
+ *      of the camera resolution in pixels.
+ *
+ * frame-rates
+ *      Values:         <numerator, uint32_t>/<denominator, uint32_t>
+ *
+ *      List of XENCAMERA_FRAME_RATE_SEPARATOR separated supported frame rates
+ *      of the camera expressed as numerator and denominator of the
+ *      corresponding frame rate.
+ *
+ *------------------- Camera Request Transport Parameters ---------------------
+ *
+ * This communication path is used to deliver requests from frontend to backend
+ * and get the corresponding responses from backend to frontend,
+ * set up per virtual camera device.
+ *
+ * req-event-channel
+ *      Values:         <uint32_t>
+ *
+ *      The identifier of the Xen camera's control event channel
+ *      used to signal activity in the ring buffer.
+ *
+ * req-ring-ref
+ *      Values:         <uint32_t>
+ *
+ *      The Xen grant reference granting permission for the backend to map
+ *      a sole page of camera's control ring buffer.
+ *
+ *-------------------- Camera Event Transport Parameters ----------------------
+ *
+ * This communication path is used to deliver asynchronous events from backend
+ * to frontend, set up per virtual camera device.
+ *
+ * evt-event-channel
+ *      Values:         <uint32_t>
+ *
+ *      The identifier of the Xen camera's event channel
+ *      used to signal activity in the ring buffer.
+ *
+ * evt-ring-ref
+ *      Values:         <uint32_t>
+ *
+ *      The Xen grant reference granting permission for the backend to map
+ *      a sole page of camera's event ring buffer.
+ */
+
+/*
+ ******************************************************************************
+ *                               STATE DIAGRAMS
+ ******************************************************************************
+ *
+ * Tool stack creates front and back state nodes with initial state
+ * XenbusStateInitialising.
+ * Tool stack creates and sets up frontend camera configuration
+ * nodes per domain.
+ *
+ *-------------------------------- Normal flow --------------------------------
+ *
+ * Front                                Back
+ * =================================    =====================================
+ * XenbusStateInitialising              XenbusStateInitialising
+ *                                       o Query backend device identification
+ *                                         data.
+ *                                       o Open and validate backend device.
+ *                                                |
+ *                                                |
+ *                                                V
+ *                                      XenbusStateInitWait
+ *
+ * o Query frontend configuration
+ * o Allocate and initialize
+ *   event channels per configured
+ *   camera.
+ * o Publish transport parameters
+ *   that will be in effect during
+ *   this connection.
+ *              |
+ *              |
+ *              V
+ * XenbusStateInitialised
+ *
+ *                                       o Query frontend transport parameters.
+ *                                       o Connect to the event channels.
+ *                                                |
+ *                                                |
+ *                                                V
+ *                                      XenbusStateConnected
+ *
+ *  o Create and initialize OS
+ *    virtual camera as per
+ *    configuration.
+ *              |
+ *              |
+ *              V
+ * XenbusStateConnected
+ *
+ *                                      XenbusStateUnknown
+ *                                      XenbusStateClosed
+ *                                      XenbusStateClosing
+ * o Remove virtual camera device
+ * o Remove event channels
+ *              |
+ *              |
+ *              V
+ * XenbusStateClosed
+ *
+ *------------------------------- Recovery flow -------------------------------
+ *
+ * In case of frontend unrecoverable errors backend handles that as
+ * if frontend goes into the XenbusStateClosed state.
+ *
+ * In case of backend unrecoverable errors frontend tries removing
+ * the virtualized device. If this is possible at the moment of error,
+ * then frontend goes into the XenbusStateInitialising state and is ready for
+ * new connection with backend. If the virtualized device is still in use and
+ * cannot be removed, then frontend goes into the XenbusStateReconfiguring state
+ * until either the virtualized device is removed or backend initiates a new
+ * connection. On the virtualized device removal frontend goes into the
+ * XenbusStateInitialising state.
+ *
+ * Note on XenbusStateReconfiguring state of the frontend: if backend has
+ * unrecoverable errors then frontend cannot send requests to the backend
+ * and thus cannot provide functionality of the virtualized device anymore.
+ * After backend is back to normal the virtualized device may still hold some
+ * state: configuration in use, allocated buffers, client application state etc.
+ * In most cases, this will require frontend to implement complex recovery
+ * reconnect logic. Instead, by going into XenbusStateReconfiguring state,
+ * frontend will make sure no new clients of the virtualized device are
+ * accepted, allow existing client(s) to exit gracefully by signaling error
+ * state etc.
+ * Once all the clients are gone frontend can reinitialize the virtualized
+ * device and get into XenbusStateInitialising state again signaling the
+ * backend that a new connection can be made.
+ *
+ * There are multiple conditions possible under which frontend will go from
+ * XenbusStateReconfiguring into XenbusStateInitialising, some of them are OS
+ * specific. For example:
+ * 1. The underlying OS framework may provide callbacks to signal that the last
+ *    client of the virtualized device has gone and the device can be removed
+ * 2. Frontend can schedule a deferred work (timer/tasklet/workqueue)
+ *    to periodically check if this is the right time to re-try removal of
+ *    the virtualized device.
+ * 3. By any other means.
+ *
+ ******************************************************************************
+ *                             REQUEST CODES
+ ******************************************************************************
+ */
+#define XENCAMERA_OP_CONFIG_SET        0x00
+#define XENCAMERA_OP_CONFIG_GET        0x01
+#define XENCAMERA_OP_CONFIG_VALIDATE   0x02
+#define XENCAMERA_OP_FRAME_RATE_SET    0x03
+#define XENCAMERA_OP_BUF_GET_LAYOUT    0x04
+#define XENCAMERA_OP_BUF_REQUEST       0x05
+#define XENCAMERA_OP_BUF_CREATE        0x06
+#define XENCAMERA_OP_BUF_DESTROY       0x07
+#define XENCAMERA_OP_BUF_QUEUE         0x08
+#define XENCAMERA_OP_BUF_DEQUEUE       0x09
+#define XENCAMERA_OP_CTRL_ENUM         0x0a
+#define XENCAMERA_OP_CTRL_SET          0x0b
+#define XENCAMERA_OP_CTRL_GET          0x0c
+#define XENCAMERA_OP_STREAM_START      0x0d
+#define XENCAMERA_OP_STREAM_STOP       0x0e
+
+#define XENCAMERA_CTRL_BRIGHTNESS      0
+#define XENCAMERA_CTRL_CONTRAST        1
+#define XENCAMERA_CTRL_SATURATION      2
+#define XENCAMERA_CTRL_HUE             3
+
+/* Number of supported controls. */
+#define XENCAMERA_MAX_CTRL             4
+
+/* Control is read-only. */
+#define XENCAMERA_CTRL_FLG_RO          (1 << 0)
+/* Control is write-only. */
+#define XENCAMERA_CTRL_FLG_WO          (1 << 1)
+/* Control's value is volatile. */
+#define XENCAMERA_CTRL_FLG_VOLATILE    (1 << 2)
+
+/* Supported color spaces. */
+#define XENCAMERA_COLORSPACE_DEFAULT   0
+#define XENCAMERA_COLORSPACE_SMPTE170M 1
+#define XENCAMERA_COLORSPACE_REC709    2
+#define XENCAMERA_COLORSPACE_SRGB      3
+#define XENCAMERA_COLORSPACE_OPRGB     4
+#define XENCAMERA_COLORSPACE_BT2020    5
+#define XENCAMERA_COLORSPACE_DCI_P3    6
+
+/* Color space transfer function. */
+#define XENCAMERA_XFER_FUNC_DEFAULT    0
+#define XENCAMERA_XFER_FUNC_709        1
+#define XENCAMERA_XFER_FUNC_SRGB       2
+#define XENCAMERA_XFER_FUNC_OPRGB      3
+#define XENCAMERA_XFER_FUNC_NONE       4
+#define XENCAMERA_XFER_FUNC_DCI_P3     5
+#define XENCAMERA_XFER_FUNC_SMPTE2084  6
+
+/* Color space Y’CbCr encoding. */
+#define XENCAMERA_YCBCR_ENC_IGNORE           0
+#define XENCAMERA_YCBCR_ENC_601              1
+#define XENCAMERA_YCBCR_ENC_709              2
+#define XENCAMERA_YCBCR_ENC_XV601            3
+#define XENCAMERA_YCBCR_ENC_XV709            4
+#define XENCAMERA_YCBCR_ENC_BT2020           5
+#define XENCAMERA_YCBCR_ENC_BT2020_CONST_LUM 6
+
+/* Quantization range. */
+#define XENCAMERA_QUANTIZATION_DEFAULT       0
+#define XENCAMERA_QUANTIZATION_FULL_RANGE    1
+#define XENCAMERA_QUANTIZATION_LIM_RANGE     2
+
+/*
+ ******************************************************************************
+ *                                 EVENT CODES
+ ******************************************************************************
+ */
+#define XENCAMERA_EVT_FRAME_AVAIL      0x00
+#define XENCAMERA_EVT_CTRL_CHANGE      0x01
+
+/*
+ ******************************************************************************
+ *               XENSTORE FIELD AND PATH NAME STRINGS, HELPERS
+ ******************************************************************************
+ */
+#define XENCAMERA_DRIVER_NAME          "vcamera"
+
+#define XENCAMERA_LIST_SEPARATOR       ","
+#define XENCAMERA_RESOLUTION_SEPARATOR "x"
+#define XENCAMERA_FRACTION_SEPARATOR   "/"
+
+#define XENCAMERA_FIELD_BE_VERSIONS    "versions"
+#define XENCAMERA_FIELD_FE_VERSION     "version"
+#define XENCAMERA_FIELD_REQ_RING_REF   "req-ring-ref"
+#define XENCAMERA_FIELD_REQ_CHANNEL    "req-event-channel"
+#define XENCAMERA_FIELD_EVT_RING_REF   "evt-ring-ref"
+#define XENCAMERA_FIELD_EVT_CHANNEL    "evt-event-channel"
+#define XENCAMERA_FIELD_MAX_BUFFERS    "max-buffers"
+#define XENCAMERA_FIELD_CONTROLS       "controls"
+#define XENCAMERA_FIELD_FORMATS        "formats"
+#define XENCAMERA_FIELD_FRAME_RATES    "frame-rates"
+#define XENCAMERA_FIELD_BE_ALLOC       "be-alloc"
+#define XENCAMERA_FIELD_UNIQUE_ID      "unique-id"
+
+#define XENCAMERA_CTRL_BRIGHTNESS_STR  "brightness"
+#define XENCAMERA_CTRL_CONTRAST_STR    "contrast"
+#define XENCAMERA_CTRL_SATURATION_STR  "saturation"
+#define XENCAMERA_CTRL_HUE_STR         "hue"
+
+#define XENCAMERA_FOURCC_BIGENDIAN_STR "-BE"
+
+/* Maximum number of buffer planes supported. */
+#define XENCAMERA_MAX_PLANE            4
+
+/*
+ ******************************************************************************
+ *                          STATUS RETURN CODES
+ ******************************************************************************
+ *
+ * Status return code is zero on success and -XEN_EXX on failure.
+ *
+ ******************************************************************************
+ *                              Assumptions
+ ******************************************************************************
+ *
+ * - usage of grant reference 0 as invalid grant reference:
+ *   grant reference 0 is valid, but never exposed to a PV driver,
+ *   because of the fact it is already in use/reserved by the PV console.
+ * - all references in this document to page sizes must be treated
+ *   as pages of size XEN_PAGE_SIZE unless otherwise noted.
+ * - all FOURCC mappings used for configuration and messaging are
+ *   Linux V4L2 ones: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/videodev2.h
+ *   with the following exceptions:
+ *     - characters are allowed in [0x20; 0x7f] range
+ *     - when used for XenStore configuration entries the following
+ *       are not allowed:
+ *       - '/', '\', ' ' (space), '<', '>', ':', '"', '|', '?', '*'
+ *       - if trailing spaces are part of the FOURCC code then those must be
+ *         trimmed
+ *
+ *
+ ******************************************************************************
+ *       Description of the protocol between frontend and backend driver
+ ******************************************************************************
+ *
+ * The two halves of a Para-virtual camera driver communicate with
+ * each other using shared pages and event channels.
+ * Shared page contains a ring with request/response packets.
+ *
+ * All reserved fields in the structures below must be 0.
+ *
+ * For all request/response/event packets:
+ *   - frame rate parameter is represented as a pair of 4 octet long
+ *     numerator and denominator:
+ *       - frame_rate_numer - uint32_t, numerator of the frame rate
+ *       - frame_rate_denom - uint32_t, denominator of the frame rate
+ *     The corresponding frame rate (Hz) is calculated as:
+ *       frame_rate = frame_rate_numer / frame_rate_denom
+ *   - buffer index is a zero based index of the buffer. Must be less than
+ *     the value of XENCAMERA_OP_CONFIG_SET.num_bufs response:
+ *       - index - uint8_t, index of the buffer.
+ *
+ *
+ *---------------------------------- Requests ---------------------------------
+ *
+ * All request packets have the same length (64 octets).
+ * All request packets have common header:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |    operation   |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ *   id - uint16_t, private guest value, echoed in response.
+ *   operation - uint8_t, operation code, XENCAMERA_OP_XXX.
+ *
+ *
+ * Request to set/validate the configuration - request to set the
+ * configuration/mode of the camera (XENCAMERA_OP_CONFIG_SET) or to
+ * check if the configuration is valid and can be used
+ * (XENCAMERA_OP_CONFIG_VALIDATE):
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_CONFIG_XXX |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                            pixel format                           | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                               width                               | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                               height                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 24
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * pixel_format - uint32_t, pixel format to be used, FOURCC code.
+ * width - uint32_t, width in pixels.
+ * height - uint32_t, height in pixels.
+ *
+ * See response format for this request.
+ *
+ * Notes:
+ *  - the only difference between XENCAMERA_OP_CONFIG_VALIDATE and
+ *    XENCAMERA_OP_CONFIG_SET is that the former doesn't actually change
+ *    camera configuration, but queries if the configuration is valid.
+ *    This can be used while stream is active and/or buffers allocated.
+ *  - frontend must check the corresponding response in order to see
+ *    if the values reported back by the backend do match the desired ones
+ *    and can be accepted.
+ *  - frontend may send multiple XENCAMERA_OP_CONFIG_SET requests before
+ *    sending XENCAMERA_OP_STREAM_START request to update or tune the
+ *    final stream configuration.
+ *  - configuration cannot be changed during active streaming, e.g.
+ *    after XENCAMERA_OP_STREAM_START and before XENCAMERA_OP_STREAM_STOP
+ *    requests.
+ */
+struct xencamera_config_req {
+    uint32_t pixel_format;
+    uint32_t width;
+    uint32_t height;
+};
+
+/*
+ * Request current configuration of the camera:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_CONFIG_GET |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * See response format for this request.
+ *
+ *
+ * Request to set the frame rate of the stream:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _FRAME_RATE_SET|   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                          frame_rate_numer                         | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                          frame_rate_denom                         | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * frame_rate_numer - uint32_t, numerator of the frame rate.
+ * frame_rate_denom - uint32_t, denominator of the frame rate.
+ *
+ * Notes:
+ *  - to query the current (actual) frame rate use XENCAMERA_OP_CONFIG_GET
+ *    request.
+ *  - this request can be used with camera buffers allocated, but stream
+ *    stopped, e.g. frontend is allowed to stop the stream with
+ *    XENCAMERA_OP_STREAM_STOP, hold the buffers allocated (e.g. keep the
+ *    configuration set with XENCAMERA_OP_CONFIG_SET), change the
+ *    frame rate of the stream and (re)start the stream again with
+ *    XENCAMERA_OP_STREAM_START.
+ *  - frame rate cannot be changed during active streaming, e.g.
+ *    after XENCAMERA_OP_STREAM_START and before XENCAMERA_OP_STREAM_STOP
+ *    commands.
+ */
+struct xencamera_frame_rate_req {
+    uint32_t frame_rate_numer;
+    uint32_t frame_rate_denom;
+};
+
+/*
+ * Request camera buffer's layout:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _BUF_GET_LAYOUT|   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * See response format for this request.
+ *
+ *
+ * Request number of buffers to be used:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_BUF_REQUEST|   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |    num_bufs    |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * num_bufs - uint8_t, desired number of buffers to be used.
+ *
+ * If num_bufs is not zero then the backend validates the requested number of
+ * buffers and responds with the number of buffers allowed for this frontend.
+ * Frontend is responsible for checking the corresponding response in order to
+ * see if the values reported back by the backend do match the desired ones
+ * and can be accepted.
+ * Frontend is allowed to send multiple XENCAMERA_OP_BUF_REQUEST requests
+ * before sending XENCAMERA_OP_STREAM_START request to update or tune the
+ * final configuration.
+ * Frontend is not allowed to change the number of buffers and/or camera
+ * configuration after the streaming has started.
+ *
+ * If num_bufs is 0 and streaming has not started yet, then the backend will
+ * free all previously allocated buffers (if any).
+ * Trying to call this if streaming is in progress will result in an error.
+ *
+ * If camera reconfiguration is required then the streaming must be stopped
+ * and this request must be sent with num_bufs set to zero and finally
+ * buffers destroyed.
+ *
+ * Please note, that the number of buffers in this request must not exceed
+ * the value configured in XenStore.max-buffers.
+ *
+ * See response format for this request.
+ */
+struct xencamera_buf_request {
+    uint8_t num_bufs;
+};
+
+/*
+ * Request camera buffer creation:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_BUF_CREATE |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |      index     |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                           plane_offset[0]                         | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                           plane_offset[1]                         | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                           plane_offset[2]                         | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                           plane_offset[3]                         | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                           gref_directory                          | 32
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 36
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * An attempt to create multiple buffers with the same index is an error.
+ * index can be re-used after destroying the corresponding camera buffer.
+ *
+ * index - uint8_t, index of the buffer to be created in the range
+ *   from 0 to the num_bufs field returned in response for
+ *   XENCAMERA_OP_BUF_REQUEST request
+ * plane_offset - array of uint32_t, offset of the corresponding plane
+ *   in octets from the buffer start. Number of offsets returned is
+ *   equal to the value returned in XENCAMERA_OP_BUF_GET_LAYOUT.num_planes.
+ * gref_directory - grant_ref_t, a reference to the first shared page
+ *   describing shared buffer references. The size of the buffer is equal to
+ *   XENCAMERA_OP_BUF_GET_LAYOUT.size response. At least one page exists. If
+ *   shared buffer size exceeds what can be addressed by this single page,
+ *   then reference to the next shared page must be supplied (see
+ *   gref_dir_next_page below).
+ *
+ * If XENCAMERA_FIELD_BE_ALLOC configuration entry is set, then backend will
+ * allocate the buffer with the parameters provided in this request and page
+ * directory is handled as follows:
+ *   Frontend on request:
+ *     - allocates pages for the directory (gref_directory,
+ *       gref_dir_next_page(s)
+ *     - grants permissions for the pages of the directory to the backend
+ *     - sets gref_dir_next_page fields
+ *   Backend on response:
+ *     - grants permissions for the pages of the buffer allocated to
+ *       the frontend
+ *     - fills in page directory with grant references
+ *       (gref[] in struct xencamera_page_directory)
+ */
+struct xencamera_buf_create_req {
+    uint8_t index;
+    uint8_t reserved[3];
+    uint32_t plane_offset[XENCAMERA_MAX_PLANE];
+    grant_ref_t gref_directory;
+};
+
+/*
+ * Shared page for XENCAMERA_OP_BUF_CREATE buffer descriptor (gref_directory in
+ * the request) employs a list of pages, describing all pages of the shared
+ * data buffer:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |                        gref_dir_next_page                         | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                              gref[0]                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                              gref[i]                              | i*4+8
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             gref[N - 1]                           | N*4+8
+ * +----------------+----------------+----------------+----------------+
+ *
+ * gref_dir_next_page - grant_ref_t, reference to the next page describing
+ *   page directory. Must be 0 if there are no more pages in the list.
+ * gref[i] - grant_ref_t, reference to a shared page of the buffer
+ *   allocated at XENCAMERA_OP_BUF_CREATE.
+ *
+ * Number of grant_ref_t entries in the whole page directory is not
+ * passed, but instead can be calculated as:
+ *   num_grefs_total = (XENCAMERA_OP_BUF_REQUEST.size + XEN_PAGE_SIZE - 1) /
+ *       XEN_PAGE_SIZE
+ */
+struct xencamera_page_directory {
+    grant_ref_t gref_dir_next_page;
+    grant_ref_t gref[1]; /* Variable length */
+};
+
+/*
+ * Request buffer destruction - destroy a previously allocated camera buffer:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_BUF_DESTROY|   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |      index     |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * index - uint8_t, index of the buffer to be destroyed.
+ *
+ *
+ * Request queueing of the buffer for backend use:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_BUF_QUEUE  |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |      index     |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * Notes:
+ *  - frontends must not access the buffer content after this request until
+ *    response to XENCAMERA_OP_BUF_DEQUEUE has been received.
+ *  - buffers must be queued to the backend before destroying them with
+ *    XENCAMERA_OP_BUF_DESTROY.
+ *
+ * index - uint8_t, index of the buffer to be queued.
+ *
+ *
+ * Request dequeueing of the buffer for frontend use:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |_OP_BUF_DEQUEUE |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |      index     |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * Notes:
+ *  - frontend is allowed to access the buffer content after the corresponding
+ *    response to this request.
+ *
+ * index - uint8_t, index of the buffer to be queued.
+ *
+ *
+ * Request camera control details:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_CTRL_ENUM  |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |      index     |                     reserved                     | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 12
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * See response format for this request.
+ *
+ * index - uint8_t, index of the control to be queried.
+ */
+struct xencamera_index {
+    uint8_t index;
+};
+
+/*
+ * Request camera control change:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |  _OP_SET_CTRL  |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |       type     |                     reserved                     | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                          value low 32-bit                         | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                          value high 32-bit                        | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 28
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * type - uint8_t, type of the control, one of the XENCAMERA_CTRL_XXX.
+ * value - int64_t, new value of the control.
+ */
+struct xencamera_ctrl_value {
+    uint8_t type;
+    uint8_t reserved[7];
+    int64_t value;
+};
+
+/*
+ * Request camera control state:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |  _OP_GET_CTRL  |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |       type     |                     reserved                     | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 12
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * See response format for this request.
+ *
+ * type - uint8_t, type of the control, one of the XENCAMERA_CTRL_XXX.
+ */
+struct xencamera_get_ctrl_req {
+    uint8_t type;
+};
+
+/*
+ * Request camera capture stream start:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |_OP_STREAM_START|   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ *
+ * Request camera capture stream stop:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |_OP_STREAM_STOP |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ *
+ *---------------------------------- Responses --------------------------------
+ *
+ * All response packets have the same length (64 octets).
+ *
+ * All response packets have common header:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |    operation   |    reserved    | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                              status                               | 8
+ * +----------------+----------------+----------------+----------------+
+ *
+ * id - uint16_t, copied from the request.
+ * operation - uint8_t, XENCAMERA_OP_* - copied from request.
+ * status - int32_t, response status, zero on success and -XEN_EXX on failure.
+ *
+ *
+ * Configuration response - response for XENCAMERA_OP_CONFIG_SET,
+ * XENCAMERA_OP_CONFIG_GET and XENCAMERA_OP_CONFIG_VALIDATE requests:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_CONFIG_XXX |    reserved    | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                               status                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                            pixel format                           | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                               width                               | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                               height                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                             colorspace                            | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                             xfer_func                             | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                             ycbcr_enc                             | 32
+ * +----------------+----------------+----------------+----------------+
+ * |                            quantization                           | 36
+ * +----------------+----------------+----------------+----------------+
+ * |                       displ_asp_ratio_numer                       | 40
+ * +----------------+----------------+----------------+----------------+
+ * |                       displ_asp_ratio_denom                       | 44
+ * +----------------+----------------+----------------+----------------+
+ * |                          frame_rate_numer                         | 48
+ * +----------------+----------------+----------------+----------------+
+ * |                          frame_rate_denom                         | 52
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 56
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * Meaning of the corresponding values in this response is the same as for
+ * XENCAMERA_OP_CONFIG_SET and XENCAMERA_OP_FRAME_RATE_SET requests.
+ *
+ * colorspace - uint32_t, this supplements pixel_format parameter,
+ *   one of the XENCAMERA_COLORSPACE_XXX.
+ * xfer_func - uint32_t, this supplements colorspace parameter,
+ *   one of the XENCAMERA_XFER_FUNC_XXX.
+ * ycbcr_enc - uint32_t, this supplements colorspace parameter,
+ *   one of the XENCAMERA_YCBCR_ENC_XXX. Please note, that ycbcr_enc is only
+ *   valid for YCbCr pixelformats and should be ignored otherwise.
+ * quantization - uint32_t, this supplements colorspace parameter,
+ *   one of the XENCAMERA_QUANTIZATION_XXX.
+ * displ_asp_ratio_numer - uint32_t, numerator of the display aspect ratio.
+ * displ_asp_ratio_denom - uint32_t, denominator of the display aspect ratio.
+ */
+struct xencamera_config_resp {
+    uint32_t pixel_format;
+    uint32_t width;
+    uint32_t height;
+    uint32_t colorspace;
+    uint32_t xfer_func;
+    uint32_t ycbcr_enc;
+    uint32_t quantization;
+    uint32_t displ_asp_ratio_numer;
+    uint32_t displ_asp_ratio_denom;
+    uint32_t frame_rate_numer;
+    uint32_t frame_rate_denom;
+};
+
+/*
+ * Request buffer response - response for XENCAMERA_OP_BUF_GET_LAYOUT
+ * request:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |_BUF_GET_LAYOUT |    reserved    | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                               status                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |   num_planes   |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                                size                               | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                           plane_size[0]                           | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                           plane_size[1]                           | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                           plane_size[2]                           | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                           plane_size[3]                           | 32
+ * +----------------+----------------+----------------+----------------+
+ * |                          plane_stride[0]                          | 36
+ * +----------------+----------------+----------------+----------------+
+ * |                          plane_stride[1]                          | 40
+ * +----------------+----------------+----------------+----------------+
+ * |                          plane_stride[2]                          | 44
+ * +----------------+----------------+----------------+----------------+
+ * |                          plane_stride[3]                          | 48
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * num_planes - uint8_t, number of planes of the buffer.
+ * size - uint32_t, overall size of the buffer including sizes of the
+ *   individual planes and padding if applicable.
+ * plane_size - array of uint32_t, size in octets of the corresponding plane
+ *   including padding.
+ * plane_stride - array of uint32_t, size in octets occupied by the
+ *   corresponding single image line including padding if applicable.
+ *
+ * Note! The sizes and strides in this response apply to all buffers created
+ * with XENCAMERA_OP_BUF_CREATE command, but individual buffers may have
+ * different plane offsets, see XENCAMERA_OP_BUF_REQUEST.plane_offset.
+ */
+struct xencamera_buf_get_layout_resp {
+    uint8_t num_planes;
+    uint8_t reserved[3];
+    uint32_t size;
+    uint32_t plane_size[XENCAMERA_MAX_PLANE];
+    uint32_t plane_stride[XENCAMERA_MAX_PLANE];
+};
+
+/*
+ * Request buffer response - response for XENCAMERA_OP_BUF_REQUEST
+ * request:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |_OP_BUF_REQUEST |    reserved    | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                               status                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |   num_buffers  |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * num_buffers - uint8_t, number of buffers to be used.
+ *
+ *
+ * Control enumerate response - response for XENCAMERA_OP_CTRL_ENUM:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_CTRL_ENUM  |    reserved    | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                               status                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |     index      |      type      |            reserved             | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                               flags                               | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                          min low 32-bits                          | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                          min high 32-bits                         | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                          max low 32-bits                          | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                          max high 32-bits                         | 32
+ * +----------------+----------------+----------------+----------------+
+ * |                         step low 32-bits                          | 36
+ * +----------------+----------------+----------------+----------------+
+ * |                         step high 32-bits                         | 40
+ * +----------------+----------------+----------------+----------------+
+ * |                        def_val low 32-bits                        | 44
+ * +----------------+----------------+----------------+----------------+
+ * |                        def_val high 32-bits                       | 48
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 52
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * index - uint8_t, index of the camera control in response.
+ * type - uint8_t, type of the control, one of the XENCAMERA_CTRL_XXX.
+ * flags - uint32_t, flags of the control, one of the XENCAMERA_CTRL_FLG_XXX.
+ * min - int64_t, minimum value of the control.
+ * max - int64_t, maximum value of the control.
+ * step - int64_t, minimum size in which control value can be changed.
+ * def_val - int64_t, default value of the control.
+ */
+struct xencamera_ctrl_enum_resp {
+    uint8_t index;
+    uint8_t type;
+    uint8_t reserved[2];
+    uint32_t flags;
+    int64_t min;
+    int64_t max;
+    int64_t step;
+    int64_t def_val;
+};
+
+/*
+ * Get control response - response for XENCAMERA_OP_CTRL_GET:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_CTRL_GET   |    reserved    | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                               status                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |       type     |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                          value low 32-bit                         | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                          value high 32-bit                        | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 32
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * type - uint8_t, type of the control, one of the XENCAMERA_CTRL_XXX.
+ * value - int64_t, new value of the control.
+ */
+
+/*
+ *----------------------------------- Events ----------------------------------
+ *
+ * Events are sent via a shared page allocated by the front and propagated by
+ *   evt-event-channel/evt-ring-ref XenStore entries.
+ *
+ * All event packets have the same length (64 octets).
+ * All event packets have common header:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |      type      |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ *
+ * id - uint16_t, event id, may be used by front.
+ * type - uint8_t, type of the event.
+ *
+ *
+ * Frame captured event - event from back to front when a new captured
+ * frame is available:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |_EVT_FRAME_AVAIL|   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |      index     |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                              used_sz                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                              seq_num                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 24
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * index - uint8_t, index of the buffer that contains new captured frame,
+ *   see XENCAMERA_OP_BUF_CREATE description on the range
+ * used_sz - uint32_t, number of octets this frame has. This can be less
+ * than the XENCAMERA_OP_BUF_REQUEST.size (response) for compressed formats.
+ * seq_num - uint32_t, sequential number of the frame. Must be
+ *   monotonically increasing. If skips are detected in seq_num then that
+ *   means that the frames in-between were dropped. Note however that not
+ *   all video capture hardware is capable of detecting dropped frames.
+ *   In that case there will be no skips in the sequence counter.
+ */
+struct xencamera_frame_avail_evt {
+    uint8_t index;
+    uint8_t reserved[3];
+    uint32_t used_sz;
+    uint32_t seq_num;
+};
+
+/*
+ * Control change event- event from back to front when camera control
+ * has changed:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |_EVT_CTRL_CHANGE|   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |       type     |                     reserved                     | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                          value low 32-bit                         | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                          value high 32-bit                        | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 28
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * type - uint8_t, type of the control, one of the XENCAMERA_CTRL_XXX.
+ * value - int64_t, new value of the control.
+ *
+ * Notes:
+ *  - this event is not sent for write-only controls
+ *  - this event is not sent to the originator of the control change
+ *  - this event is not sent when frontend first connects, e.g. initial
+ *    control state must be explicitly queried
+ */
+
+struct xencamera_req {
+    uint16_t id;
+    uint8_t operation;
+    uint8_t reserved[5];
+    union {
+        struct xencamera_config_req config;
+        struct xencamera_frame_rate_req frame_rate;
+        struct xencamera_buf_request buf_request;
+        struct xencamera_buf_create_req buf_create;
+        struct xencamera_index index;
+        struct xencamera_ctrl_value ctrl_value;
+        struct xencamera_get_ctrl_req get_ctrl;
+        uint8_t reserved[56];
+    } req;
+};
+
+struct xencamera_resp {
+    uint16_t id;
+    uint8_t operation;
+    uint8_t reserved;
+    int32_t status;
+    union {
+        struct xencamera_config_resp config;
+        struct xencamera_buf_get_layout_resp buf_layout;
+        struct xencamera_buf_request buf_request;
+        struct xencamera_ctrl_enum_resp ctrl_enum;
+        struct xencamera_ctrl_value ctrl_value;
+        uint8_t reserved1[56];
+    } resp;
+};
+
+struct xencamera_evt {
+    uint16_t id;
+    uint8_t type;
+    uint8_t reserved[5];
+    union {
+        struct xencamera_frame_avail_evt frame_avail;
+        struct xencamera_ctrl_value ctrl_value;
+        uint8_t reserved[56];
+    } evt;
+};
+
+DEFINE_RING_TYPES(xen_cameraif, struct xencamera_req, struct xencamera_resp);
+
+/*
+ ******************************************************************************
+ *                        Back to front events delivery
+ ******************************************************************************
+ * In order to deliver asynchronous events from back to front a shared page is
+ * allocated by front and its granted reference propagated to back via
+ * XenStore entries (evt-ring-ref/evt-event-channel).
+ * This page has a common header used by both front and back to synchronize
+ * access and control event's ring buffer, while back being a producer of the
+ * events and front being a consumer. The rest of the page after the header
+ * is used for event packets.
+ *
+ * Upon reception of an event(s) front may confirm its reception
+ * for either each event, group of events or none.
+ */
+
+struct xencamera_event_page {
+    uint32_t in_cons;
+    uint32_t in_prod;
+    uint8_t reserved[56];
+};
+
+#define XENCAMERA_EVENT_PAGE_SIZE 4096
+#define XENCAMERA_IN_RING_OFFS (sizeof(struct xencamera_event_page))
+#define XENCAMERA_IN_RING_SIZE (XENCAMERA_EVENT_PAGE_SIZE - XENCAMERA_IN_RING_OFFS)
+#define XENCAMERA_IN_RING_LEN (XENCAMERA_IN_RING_SIZE / sizeof(struct xencamera_evt))
+#define XENCAMERA_IN_RING(page) \
+    ((struct xencamera_evt *)((char *)(page) + XENCAMERA_IN_RING_OFFS))
+#define XENCAMERA_IN_RING_REF(page, idx) \
+    (XENCAMERA_IN_RING((page))[(idx) % XENCAMERA_IN_RING_LEN])
+
+#endif /* __XEN_PUBLIC_IO_CAMERAIF_H__ */
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */

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