[PATCH v2 0/3] A DRM API for adaptive sync and variable refresh rate support

[Wentland, Harry]

On 2018-10-12 4:31 a.m., Koenig, Christian wrote:
> Am 12.10.2018 um 10:26 schrieb Michel Dänzer:
>> On 2018-10-11 9:44 p.m., Harry Wentland wrote:
>>> On 2018-10-03 04:25 AM, Mike Lothian wrote:
>>>> I'm curious to know whether this will/could work over PRIME
>>> I don't see why this shouldn't work over PRIME as long as the
>>> presenting GPU supports the new variable refresh rate API, but I know
>>> very little about prime, so maybe someone else can chime in and give
>>> a better opinion.
>> It won't work for displays connected to a secondary GPU, because those
>> aren't hooked up to the Present extension directly.
>>
>> It can theoretically work with render offloading, if the primary GPU can
>> scan out directly from the shared pixmap. This is only possible with
>> current AMD APUs which support scatter/gather scanout (Carrizo and
>> newer?).
> 
> Actually only Carizzo and Stoney at the moment because this is buggy on 
> Raven. Not sure if that is a pure software or a hardware problem.
> 
> Christian.
> 
>> One gotcha is that xf86-video-amdgpu currently doesn't allow
>> flipping between buffers with different tiling parameters (BTW Harry,
>> does that work with DC?), but that should be easy to fix.
> 

Not currently. Fixable, but unfortunately not as easy as I'd hope. The good news is that I'm planning to rework that code so it would be easy to fix or should just happen on a per-flip basis.

Harry