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

[Marek Olšák]

On Thu, Sep 15, 2016 at 5:14 AM, Dave Airlie <airlied at gmail.com> wrote:
> 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.

The main problem is that nouveau lacks a proper memory management and
buffers are pinned after allocation forever.

The workaround is to add PIPE_BIND_something, which would do what you
need it to do, and use it where you need to use it. I don't care about
the name as long as it works for nouveau. Does that sound reasonable?

Marek