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

[Michel Dänzer]

On 18/08/16 04:41 PM, Christian König wrote:
>> Afaiu the prime importing display gpu generates its own gem buffer
>> handle (prime_fd_to_handle) from that dmabuf, importing scather-gather
>> tables to access the dmabuf in system ram. As far as page flipping is
>> concerned, so far those gem buffers / radeon_bo's aren't treated any
>> different than native ones. During pageflip setup they get pinned into
>> VRAM, which moves (=copies) their content from the RAM dmabuf backing
>> store into VRAM. 
> 
> Your understanding isn't correct. Buffers imported using prime always
> stay in GTT, they can't be moved to VRAM.

That's the theory, but based on Mario's description it's clear that
there is at least one bug which either actually allows a shared buffer
to be moved to VRAM, or at least doesn't propagate the error correctly,
so the page flip operation "succeeds".


> It's the DDX which copies the buffer content from the imported prime
> handle into a native on which is enabled to scan out.

There is no such code which could explain what Mario is seeing.


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