[v10,6/6] Documentation: iio: Document high-speed DMABUF based API
Commit Message
Document the new DMABUF based API.
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
v2: - Explicitly state that the new interface is optional and is
not implemented by all drivers.
- The IOCTLs can now only be called on the buffer FD returned by
IIO_BUFFER_GET_FD_IOCTL.
- Move the page up a bit in the index since it is core stuff and not
driver-specific.
v3: Update the documentation to reflect the new API.
v5: Use description lists for the documentation of the three new IOCTLs
instead of abusing subsections.
v8: Renamed dmabuf_api.rst -> iio_dmabuf_api.rst, and updated index.rst
whose format changed in iio/togreg.
---
Documentation/iio/iio_dmabuf_api.rst | 54 ++++++++++++++++++++++++++++
Documentation/iio/index.rst | 1 +
2 files changed, 55 insertions(+)
create mode 100644 Documentation/iio/iio_dmabuf_api.rst
Comments
Hi,
On 6/5/24 4:08 AM, Paul Cercueil wrote:
> Document the new DMABUF based API.
>
> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> Signed-off-by: Nuno Sa <nuno.sa@analog.com>
>
> ---
> v2: - Explicitly state that the new interface is optional and is
> not implemented by all drivers.
> - The IOCTLs can now only be called on the buffer FD returned by
> IIO_BUFFER_GET_FD_IOCTL.
> - Move the page up a bit in the index since it is core stuff and not
> driver-specific.
>
> v3: Update the documentation to reflect the new API.
>
> v5: Use description lists for the documentation of the three new IOCTLs
> instead of abusing subsections.
>
> v8: Renamed dmabuf_api.rst -> iio_dmabuf_api.rst, and updated index.rst
> whose format changed in iio/togreg.
> ---
> Documentation/iio/iio_dmabuf_api.rst | 54 ++++++++++++++++++++++++++++
> Documentation/iio/index.rst | 1 +
> 2 files changed, 55 insertions(+)
> create mode 100644 Documentation/iio/iio_dmabuf_api.rst
>
> diff --git a/Documentation/iio/iio_dmabuf_api.rst b/Documentation/iio/iio_dmabuf_api.rst
> new file mode 100644
> index 000000000000..1cd6cd51a582
> --- /dev/null
> +++ b/Documentation/iio/iio_dmabuf_api.rst
> @@ -0,0 +1,54 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +===================================
> +High-speed DMABUF interface for IIO
> +===================================
> +
> +1. Overview
> +===========
> +
> +The Industrial I/O subsystem supports access to buffers through a
> +file-based interface, with read() and write() access calls through the
> +IIO device's dev node.
> +
> +It additionally supports a DMABUF based interface, where the userspace
> +can attach DMABUF objects (externally created) to a IIO buffer, and
I would say/write: to an IIO buffer,
> +subsequently use them for data transfers.
> +
> +A userspace application can then use this interface to share DMABUF
> +objects between several interfaces, allowing it to transfer data in a
> +zero-copy fashion, for instance between IIO and the USB stack.
> +
> +The userspace application can also memory-map the DMABUF objects, and
> +access the sample data directly. The advantage of doing this vs. the
> +read() interface is that it avoids an extra copy of the data between the
> +kernel and userspace. This is particularly useful for high-speed devices
> +which produce several megabytes or even gigabytes of data per second.
> +It does however increase the userspace-kernelspace synchronization
> +overhead, as the DMA_BUF_SYNC_START and DMA_BUF_SYNC_END IOCTLs have to
> +be used for data integrity.
> +
> +2. User API
> +===========
> +
> +As part of this interface, three new IOCTLs have been added. These three
> +IOCTLs have to be performed on the IIO buffer's file descriptor,
> +obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.
> +
> + ``IIO_BUFFER_DMABUF_ATTACH_IOCTL(int)``
(int fd)
?
> + Attach the DMABUF object, identified by its file descriptor, to the
> + IIO buffer. Returns zero on success, and a negative errno value on
> + error.
> +
> + ``IIO_BUFFER_DMABUF_DETACH_IOCTL(int)``
ditto.
> + Detach the given DMABUF object, identified by its file descriptor,
> + from the IIO buffer. Returns zero on success, and a negative errno
> + value on error.
> +
> + Note that closing the IIO buffer's file descriptor will
> + automatically detach all previously attached DMABUF objects.
> +
> + ``IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf *iio_dmabuf)``
> + Enqueue a previously attached DMABUF object to the buffer queue.
> + Enqueued DMABUFs will be read from (if output buffer) or written to
> + (if input buffer) as long as the buffer is enabled.
thanks.
Hi Randy,
Le jeudi 06 juin 2024 à 10:32 -0700, Randy Dunlap a écrit :
> Hi,
>
> On 6/5/24 4:08 AM, Paul Cercueil wrote:
> > Document the new DMABUF based API.
> >
> > Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> > Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> >
> > ---
> > v2: - Explicitly state that the new interface is optional and is
> > not implemented by all drivers.
> > - The IOCTLs can now only be called on the buffer FD returned
> > by
> > IIO_BUFFER_GET_FD_IOCTL.
> > - Move the page up a bit in the index since it is core stuff
> > and not
> > driver-specific.
> >
> > v3: Update the documentation to reflect the new API.
> >
> > v5: Use description lists for the documentation of the three new
> > IOCTLs
> > instead of abusing subsections.
> >
> > v8: Renamed dmabuf_api.rst -> iio_dmabuf_api.rst, and updated
> > index.rst
> > whose format changed in iio/togreg.
> > ---
> > Documentation/iio/iio_dmabuf_api.rst | 54
> > ++++++++++++++++++++++++++++
> > Documentation/iio/index.rst | 1 +
> > 2 files changed, 55 insertions(+)
> > create mode 100644 Documentation/iio/iio_dmabuf_api.rst
> >
> > diff --git a/Documentation/iio/iio_dmabuf_api.rst
> > b/Documentation/iio/iio_dmabuf_api.rst
> > new file mode 100644
> > index 000000000000..1cd6cd51a582
> > --- /dev/null
> > +++ b/Documentation/iio/iio_dmabuf_api.rst
> > @@ -0,0 +1,54 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +===================================
> > +High-speed DMABUF interface for IIO
> > +===================================
> > +
> > +1. Overview
> > +===========
> > +
> > +The Industrial I/O subsystem supports access to buffers through a
> > +file-based interface, with read() and write() access calls through
> > the
> > +IIO device's dev node.
> > +
> > +It additionally supports a DMABUF based interface, where the
> > userspace
> > +can attach DMABUF objects (externally created) to a IIO buffer,
> > and
>
> I would say/write: to an IIO buffer,
Right.
> > +subsequently use them for data transfers.
> > +
> > +A userspace application can then use this interface to share
> > DMABUF
> > +objects between several interfaces, allowing it to transfer data
> > in a
> > +zero-copy fashion, for instance between IIO and the USB stack.
> > +
> > +The userspace application can also memory-map the DMABUF objects,
> > and
> > +access the sample data directly. The advantage of doing this vs.
> > the
> > +read() interface is that it avoids an extra copy of the data
> > between the
> > +kernel and userspace. This is particularly useful for high-speed
> > devices
> > +which produce several megabytes or even gigabytes of data per
> > second.
> > +It does however increase the userspace-kernelspace synchronization
> > +overhead, as the DMA_BUF_SYNC_START and DMA_BUF_SYNC_END IOCTLs
> > have to
> > +be used for data integrity.
> > +
> > +2. User API
> > +===========
> > +
> > +As part of this interface, three new IOCTLs have been added. These
> > three
> > +IOCTLs have to be performed on the IIO buffer's file descriptor,
> > +obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.
> > +
> > + ``IIO_BUFFER_DMABUF_ATTACH_IOCTL(int)``
>
> (int fd)
> ?
Yes, I can change that. Although it's very obvious what the "int" is
for, given the text above.
>
> > + Attach the DMABUF object, identified by its file descriptor,
> > to the
> > + IIO buffer. Returns zero on success, and a negative errno
> > value on
> > + error.
> > +
> > + ``IIO_BUFFER_DMABUF_DETACH_IOCTL(int)``
>
> ditto.
>
> > + Detach the given DMABUF object, identified by its file
> > descriptor,
> > + from the IIO buffer. Returns zero on success, and a negative
> > errno
> > + value on error.
> > +
> > + Note that closing the IIO buffer's file descriptor will
> > + automatically detach all previously attached DMABUF objects.
> > +
> > + ``IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf
> > *iio_dmabuf)``
> > + Enqueue a previously attached DMABUF object to the buffer
> > queue.
> > + Enqueued DMABUFs will be read from (if output buffer) or
> > written to
> > + (if input buffer) as long as the buffer is enabled.
>
> thanks.
Cheers,
-Paul
Hi Paul.
On 6/7/24 12:44 AM, Paul Cercueil wrote:
> Hi Randy,
>
> Le jeudi 06 juin 2024 à 10:32 -0700, Randy Dunlap a écrit :
>> Hi,
>>
>> On 6/5/24 4:08 AM, Paul Cercueil wrote:
>>> Document the new DMABUF based API.
>>>
>>> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
>>> Signed-off-by: Nuno Sa <nuno.sa@analog.com>
>>>
>>> ---
>>> v2: - Explicitly state that the new interface is optional and is
>>> not implemented by all drivers.
>>> - The IOCTLs can now only be called on the buffer FD returned
>>> by
>>> IIO_BUFFER_GET_FD_IOCTL.
>>> - Move the page up a bit in the index since it is core stuff
>>> and not
>>> driver-specific.
>>>
>>> v3: Update the documentation to reflect the new API.
>>>
>>> v5: Use description lists for the documentation of the three new
>>> IOCTLs
>>> instead of abusing subsections.
>>>
>>> v8: Renamed dmabuf_api.rst -> iio_dmabuf_api.rst, and updated
>>> index.rst
>>> whose format changed in iio/togreg.
>>> ---
>>> Documentation/iio/iio_dmabuf_api.rst | 54
>>> ++++++++++++++++++++++++++++
>>> Documentation/iio/index.rst | 1 +
>>> 2 files changed, 55 insertions(+)
>>> create mode 100644 Documentation/iio/iio_dmabuf_api.rst
>>>
>>> diff --git a/Documentation/iio/iio_dmabuf_api.rst
>>> b/Documentation/iio/iio_dmabuf_api.rst
>>> new file mode 100644
>>> index 000000000000..1cd6cd51a582
>>> --- /dev/null
>>> +++ b/Documentation/iio/iio_dmabuf_api.rst
>>> @@ -0,0 +1,54 @@
>>> +.. SPDX-License-Identifier: GPL-2.0
>>> +
>>> +===================================
>>> +High-speed DMABUF interface for IIO
>>> +===================================
>>> +
>>> +1. Overview
>>> +===========
>>> +
>>> +The Industrial I/O subsystem supports access to buffers through a
>>> +file-based interface, with read() and write() access calls through
>>> the
>>> +IIO device's dev node.
>>> +
>>> +It additionally supports a DMABUF based interface, where the
>>> userspace
>>> +can attach DMABUF objects (externally created) to a IIO buffer,
>>> and
>>
>> I would say/write: to an IIO buffer,
>
> Right.
>
>>> +subsequently use them for data transfers.
>>> +
>>> +A userspace application can then use this interface to share
>>> DMABUF
>>> +objects between several interfaces, allowing it to transfer data
>>> in a
>>> +zero-copy fashion, for instance between IIO and the USB stack.
>>> +
>>> +The userspace application can also memory-map the DMABUF objects,
>>> and
>>> +access the sample data directly. The advantage of doing this vs.
>>> the
>>> +read() interface is that it avoids an extra copy of the data
>>> between the
>>> +kernel and userspace. This is particularly useful for high-speed
>>> devices
>>> +which produce several megabytes or even gigabytes of data per
>>> second.
>>> +It does however increase the userspace-kernelspace synchronization
>>> +overhead, as the DMA_BUF_SYNC_START and DMA_BUF_SYNC_END IOCTLs
>>> have to
>>> +be used for data integrity.
>>> +
>>> +2. User API
>>> +===========
>>> +
>>> +As part of this interface, three new IOCTLs have been added. These
>>> three
>>> +IOCTLs have to be performed on the IIO buffer's file descriptor,
>>> +obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.
>>> +
>>> + ``IIO_BUFFER_DMABUF_ATTACH_IOCTL(int)``
>>
>> (int fd)
>> ?
>
> Yes, I can change that. Although it's very obvious what the "int" is
> for, given the text above.
>
Yes. This is just to be consistent with the text below:
+ ``IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf *iio_dmabuf)``
>>
>>> + Attach the DMABUF object, identified by its file descriptor,
>>> to the
>>> + IIO buffer. Returns zero on success, and a negative errno
>>> value on
>>> + error.
>>> +
>>> + ``IIO_BUFFER_DMABUF_DETACH_IOCTL(int)``
>>
>> ditto.
>>
>>> + Detach the given DMABUF object, identified by its file
>>> descriptor,
>>> + from the IIO buffer. Returns zero on success, and a negative
>>> errno
>>> + value on error.
>>> +
>>> + Note that closing the IIO buffer's file descriptor will
>>> + automatically detach all previously attached DMABUF objects.
>>> +
>>> + ``IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf
>>> *iio_dmabuf)``
>>> + Enqueue a previously attached DMABUF object to the buffer
>>> queue.
>>> + Enqueued DMABUFs will be read from (if output buffer) or
>>> written to
>>> + (if input buffer) as long as the buffer is enabled.
>>
>> thanks.
>
> Cheers,
> -Paul
thanks.
new file mode 100644
@@ -0,0 +1,54 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===================================
+High-speed DMABUF interface for IIO
+===================================
+
+1. Overview
+===========
+
+The Industrial I/O subsystem supports access to buffers through a
+file-based interface, with read() and write() access calls through the
+IIO device's dev node.
+
+It additionally supports a DMABUF based interface, where the userspace
+can attach DMABUF objects (externally created) to a IIO buffer, and
+subsequently use them for data transfers.
+
+A userspace application can then use this interface to share DMABUF
+objects between several interfaces, allowing it to transfer data in a
+zero-copy fashion, for instance between IIO and the USB stack.
+
+The userspace application can also memory-map the DMABUF objects, and
+access the sample data directly. The advantage of doing this vs. the
+read() interface is that it avoids an extra copy of the data between the
+kernel and userspace. This is particularly useful for high-speed devices
+which produce several megabytes or even gigabytes of data per second.
+It does however increase the userspace-kernelspace synchronization
+overhead, as the DMA_BUF_SYNC_START and DMA_BUF_SYNC_END IOCTLs have to
+be used for data integrity.
+
+2. User API
+===========
+
+As part of this interface, three new IOCTLs have been added. These three
+IOCTLs have to be performed on the IIO buffer's file descriptor,
+obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.
+
+ ``IIO_BUFFER_DMABUF_ATTACH_IOCTL(int)``
+ Attach the DMABUF object, identified by its file descriptor, to the
+ IIO buffer. Returns zero on success, and a negative errno value on
+ error.
+
+ ``IIO_BUFFER_DMABUF_DETACH_IOCTL(int)``
+ Detach the given DMABUF object, identified by its file descriptor,
+ from the IIO buffer. Returns zero on success, and a negative errno
+ value on error.
+
+ Note that closing the IIO buffer's file descriptor will
+ automatically detach all previously attached DMABUF objects.
+
+ ``IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf *iio_dmabuf)``
+ Enqueue a previously attached DMABUF object to the buffer queue.
+ Enqueued DMABUFs will be read from (if output buffer) or written to
+ (if input buffer) as long as the buffer is enabled.
@@ -9,6 +9,7 @@ Industrial I/O
iio_configfs
iio_devbuf
+ iio_dmabuf_api
iio_tools
Industrial I/O Kernel Drivers