"Fixes" for page flipping under PRIME on AMD & nouveau

[Michel Dänzer]

On 18/08/16 08:51 AM, Mario Kleiner wrote:
>
> That's what the ati-ddx/amdgpu-ddx does at the moment, as it detects the
> mismatch in tiling flags and uses the DRI3/Present copy path instead of
> the pageflip path. The problem is that the servers Present
> implementation doesn't request a vsync'ed start of the copy operation [...]

It waits for vblank before starting the copy.


> There is this other approach from NVidia's Alex Goins for their
> proprietary driver, whose patches landed in the X-Server 1.19 master
> branch a couple of weeks ago. I haven't read his patches in detail yet,
> and i so far couldn't successfully test them with the reference
> implementation in modesetting ddx 1.19. Afaik there the display gpu
> exports a pair of scanout friendly, page flipping compatible dmabufs (i
> assume linear, contiguous, accessible by the display engines),

FWIW, that wouldn't be possible with our "older" GPUs which can't scan
out from GTT: A BO can be either shared with another GPU or scanout
friendly, not both at the same time.


> and the offload gpu imports those and renders into them. That saves
> one extra copy, so should be somewhat more efficient.

Using two shared buffers actually isn't as efficient as possible wrt
inter-GPU bandwidth.


> Setting it up seems to be more involved and less flexible though. So far
> i couldn't make it work here for testing. Maybe bugs, maybe mistakes on
> my side, maybe i just have the wrong hardware for it.

Yeah, my impression has been it's a rather complicated solution geared
towards the Intel iGPU + proprietary nVidia use case.


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