Re: [PATCH v2 2/3] drm: Add variable refresh property to DRM CRTC

["Michel Dänzer" <michel-otUistvHUpPR7s880joybQ@public.gmane.org>]

On 2018-10-05 6:21 p.m., Kazlauskas, Nicholas wrote:
> On 10/05/2018 04:10 AM, Pekka Paalanen wrote:
>>
>> 2. User preference
>>     A toggle on the desktop environment's display settings
>>     application to allow or disallow VRR. After all, video mode
>>     configuration is here too, and ideally applications should not
>>     mess with the video mode directly.
>
> [...]
>
> User preference can be handled as part of the DDX driver with something
> like an X Option. Dropping the variable_refresh_enabled property in
> favor of this works. This covers 2.

The Xorg driver can expose a RandR output property, even if the kernel
doesn't expose a corresponding connector property. See e.g. the TearFree
output property in xf86-video-amdgpu.


>> I also believe that it would be useful to expose vmin/vmax to userspace
>> as properties, so that display servers and apps can plan ahead on when
>> they will render. I suppose that can be left for later when someone
>> starts working on userspace taking advantage of it, so that the proper
>> userspace requirement for new UABI is fulfilled.
> 
> Knowing the vmin/vmax could potentially be useful for testing but most
> applications shouldn't be trying to predict or adjust rendering based on
> these.

FWIW, recent research indicates that this is necessary for perfectly
smooth animation without micro-stuttering, even with VRR.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer
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