[PATCH xf86-video-amdgpu 0/6] xf86-video-amdgpu integration for DRM variable refresh rate API

[Michel Dänzer]

On 2018-09-12 2:48 p.m., Kazlauskas, Nicholas wrote:
> On 09/12/2018 04:13 AM, Michel Dänzer wrote:
>> On 2018-09-11 6:18 p.m., Nicholas Kazlauskas wrote:
>>> These patches are part of a proposed new interface for supporting
>>> variable refresh rate via DRM properties.
>>>
>>> https://patchwork.freedesktop.org/series/49486/
>>>
>>> When notified of a window that is FreeSync capable via X these
>>> patches help track when the window is fullscreen to manage the
>>> variable_refresh property on the CRTC.
>>
>> I'm afraid the Xorg driver support will have to be more or less redone
>> from scratch for upstreaming:
>>
>> Whether or not a client wants variable refresh rate enabled can be
>> tracked via the window property mechanism supported by the core X11
>> protocol, no need for a protocol extension.
>>
>> That should also allow simpler tracking of when variable refresh rate
>> can actually be enabled: It can be enabled while a window is flipping,
>> and its corresponding property allows it. This should be straightforward
>> with the Present extension, because that also explicitly marks the end
>> of a window flipping (via an "unflip"). DRI2 is trickier; it's probably
>> okay not to support variable refresh rate with that, at least initially.
>>
>>
>> I can look into this after the upcoming Xorg driver 18.1 releases. Or I
>> can give guidance if one of you wants to look into it.
> 
> I can a look into this. I agree that the extension method is less than
> ideal - in being vendor specific mostly. It does have the nice property
> that it remains independent of the application's render backend, though.

Not sure what you mean by that. Surely a window property is just as
independent. :)


> I imagine you're suggesting specifying a window property hint like
> _NET_WM_BYPASS_COMPOSITOR - maybe a define new one like
> _NET_WM_VARIABLE_REFRESH (even though the two are closely related in
> terms of fullscreen behavior). Then in each backend the property could
> probably be checked before the present as appropriate.

Right. (Not sure the _NET_WM prefix is appropriate, as it's nothing to
do with the window manager, but that's a detail)


> This patch series already has the problem you're describing about DRI2
> where there's not a nice explicit end notification for flipping - it's
> only disabled when the window no longer covers the CRTC or the window is
> destroyed (which is the case for most applications but likely not all).

Right. I think it's better to just not bother with DRI2, at least until
there's a specific scenario where variable refresh is really needed with
DRI2.


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