[RFC,02/11] drm/fb-helper: Skip writeback connectors

  Writeback connectors aren't much use to the fbdev helpers, as they won't
show anything to the user. Skip them when looking for candidate output
configurations.

Signed-off-by: Brian Starkey <brian.starkey@arm.com>
---
 drivers/gpu/drm/drm_fb_helper.c |    4 ++++
 1 file changed, 4 insertions(+)
  

On Tue, Oct 11, 2016 at 03:53:59PM +0100, Brian Starkey wrote:
> Writeback connectors aren't much use to the fbdev helpers, as they won't
> show anything to the user. Skip them when looking for candidate output
> configurations.
> 
> Signed-off-by: Brian Starkey <brian.starkey@arm.com>
> ---
>  drivers/gpu/drm/drm_fb_helper.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 03414bd..dedf6e7 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -2016,6 +2016,10 @@ static int drm_pick_crtcs(struct drm_fb_helper *fb_helper,
>  	if (modes[n] == NULL)
>  		return best_score;
>  
> +	/* Writeback connectors aren't much use for fbdev */
> +	if (connector->connector_type == DRM_MODE_CONNECTOR_WRITEBACK)
> +		return best_score;

I think we could handle this by always marking writeback connectors as
disconnected. Userspace and fbdev emulation should then avoid them,
always.
-Daniel

> +
>  	crtcs = kzalloc(fb_helper->connector_count *
>  			sizeof(struct drm_fb_helper_crtc *), GFP_KERNEL);
>  	if (!crtcs)
> -- 
> 1.7.9.5
>
  

On Tue, Oct 11, 2016 at 05:44:48PM +0200, Daniel Vetter wrote:
>On Tue, Oct 11, 2016 at 03:53:59PM +0100, Brian Starkey wrote:
>> Writeback connectors aren't much use to the fbdev helpers, as they won't
>> show anything to the user. Skip them when looking for candidate output
>> configurations.
>>
>> Signed-off-by: Brian Starkey <brian.starkey@arm.com>
>> ---
>>  drivers/gpu/drm/drm_fb_helper.c |    4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
>> index 03414bd..dedf6e7 100644
>> --- a/drivers/gpu/drm/drm_fb_helper.c
>> +++ b/drivers/gpu/drm/drm_fb_helper.c
>> @@ -2016,6 +2016,10 @@ static int drm_pick_crtcs(struct drm_fb_helper *fb_helper,
>>  	if (modes[n] == NULL)
>>  		return best_score;
>>
>> +	/* Writeback connectors aren't much use for fbdev */
>> +	if (connector->connector_type == DRM_MODE_CONNECTOR_WRITEBACK)
>> +		return best_score;
>
>I think we could handle this by always marking writeback connectors as
>disconnected. Userspace and fbdev emulation should then avoid them,
>always.
>-Daniel
>

Good idea; I'll need to take a closer look at how it would interact
with the probe helper (connector->force etc).

Are you thinking instead-of or in-addition-to the client cap? I'd be
worried about apps doing strange things and trying to use even
disconnected connectors.

>> +
>>  	crtcs = kzalloc(fb_helper->connector_count *
>>  			sizeof(struct drm_fb_helper_crtc *), GFP_KERNEL);
>>  	if (!crtcs)
>> --
>> 1.7.9.5
>>
>
>-- 
>Daniel Vetter
>Software Engineer, Intel Corporation
>http://blog.ffwll.ch
>
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On Tue, Oct 11, 2016 at 6:47 PM, Brian Starkey <brian.starkey@arm.com> wrote:
> On Tue, Oct 11, 2016 at 05:44:48PM +0200, Daniel Vetter wrote:
>>
>> On Tue, Oct 11, 2016 at 03:53:59PM +0100, Brian Starkey wrote:
>>>
>>> Writeback connectors aren't much use to the fbdev helpers, as they won't
>>> show anything to the user. Skip them when looking for candidate output
>>> configurations.
>>>
>>> Signed-off-by: Brian Starkey <brian.starkey@arm.com>
>>> ---
>>>  drivers/gpu/drm/drm_fb_helper.c |    4 ++++
>>>  1 file changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/drm_fb_helper.c
>>> b/drivers/gpu/drm/drm_fb_helper.c
>>> index 03414bd..dedf6e7 100644
>>> --- a/drivers/gpu/drm/drm_fb_helper.c
>>> +++ b/drivers/gpu/drm/drm_fb_helper.c
>>> @@ -2016,6 +2016,10 @@ static int drm_pick_crtcs(struct drm_fb_helper
>>> *fb_helper,
>>>         if (modes[n] == NULL)
>>>                 return best_score;
>>>
>>> +       /* Writeback connectors aren't much use for fbdev */
>>> +       if (connector->connector_type == DRM_MODE_CONNECTOR_WRITEBACK)
>>> +               return best_score;
>>
>>
>> I think we could handle this by always marking writeback connectors as
>> disconnected. Userspace and fbdev emulation should then avoid them,
>> always.
>> -Daniel
>>
>
> Good idea; I'll need to take a closer look at how it would interact
> with the probe helper (connector->force etc).
>
> Are you thinking instead-of or in-addition-to the client cap? I'd be
> worried about apps doing strange things and trying to use even
> disconnected connectors.

Apps shouldn't try to use disconnected connectors, at least by
default. I think we wouldn't need the cap in that case.
-Daniel