[Mesa-dev] [PATCH 09/10] st/vdpau: implement the new DMA-buf based interop

[Dave Airlie]

On 15 September 2016 at 13:03, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> On Wed, Sep 14, 2016 at 10:15 PM, Michel Dänzer <michel at daenzer.net> wrote:
>>> No, the current impl is pretty radeon-specific (note - it doesn't work
>>> on nouveau, and no other drivers support the interfaces, so ... it's
>>> radeon-specific).
>>
>> We're getting into semantics here, but since the reason it doesn't work
>> well with nouveau is a fundamental issue in nouveau (which should also
>> affect at least DRI3 in general), while you may call it "de facto radeon
>> specific" if you're so inclined, that doesn't make the implementation
>> actually radeon specific.
>
> No one's reported any issues with DRI3, I use it on my home desktop
> every day. And VDPAU used to work great until these changes to
> st/vdpau went in. Prior to those changes in st/vdpau, saying that
> "shared == gart" was a perfectly reasonable thing to say, since no one
> tried blending/readback on those surfaces (or at least not enough for
> it to matter). But now ... poof ... it doesn't work [actually, worse -
> it works - but can't come close to keeping up with 24fps video].
>
> Anyways, I realize this is a losing argument. Interfaces and usages
> move forward and change over time. This happens to be a change that
> leaves nouveau behind. As a spare-time contributor, I can't keep up
> with multiple full timers. I had hoped that there'd be some way to
> make it all still work, but that doesn't seem to be the case.
> Unfortunately end users are going to lose out on functionality as a
> result.

So (a) this is a regression, regressions aren't allowed, so it would
be good to back the change out until it can be fixed.

The problem is the combo of LINEAR and SHARED means that
GART placement is most likely, radeon should be doing the same
in most circumstances.

We should possible introduced SHARED_OTHER_GPU maybe
and use that throughout the stack where it matters.

Dave.