Am 10.04.2017 um 10:52 schrieb Michel Dänzer:
On 05/04/17 08:21 PM, Christian König wrote:
Am 05.04.2017 um 13:13 schrieb Christopher James Halse Rogers:
On Wed, Apr 5, 2017 at 8:14 PM Lucas Stach <l.st...@pengutronix.de
<mailto:l.st...@pengutronix.de>> wrote:
Am Mittwoch, den 05.04.2017, 11:59 +0200 schrieb Daniel Vetter:
> On Wed, Apr 05, 2017 at 10:15:44AM +0200, Lucas Stach wrote:
> > Am Mittwoch, den 05.04.2017, 00:20 +0000 schrieb Christopher
James Halse
> > Rogers:
> > >
> > >
> > > On Tue, Apr 4, 2017 at 9:53 PM Daniel Vetter
<dan...@ffwll.ch <mailto:dan...@ffwll.ch>> wrote:
> > >
> > > On Tue, Apr 4, 2017 at 12:43 PM, Lucas Stach
> > > <l.st...@pengutronix.de
<mailto:l.st...@pengutronix.de>> wrote:
> > > >> If I could guarantee that I'd only ever run on
> > > 4.13-or-later kernels
> > > >> (I think that's when the previous patches will
land?), then
> > > this would
> > > >> indeed be mostly unnecessary. It would save me a
bunch of
> > > addfb calls
> > > >> that would predictably fail, but they're cheap.
> > > >
> > > > I don't think we ever had caps for "things are
working now,
> > > as they are
> > > > supposed to". i915 wasn't properly synchronizing
on foreign
> > > fences for a
> > > > long time, yet we didn't gain a cap for "cross
device sync
> > > works now".
> > > >
> > > > If your distro use-case relies on those things
working it's
> > > probably
> > > > best to just backport the relevant fixes.
> > >
> > > The even better solution for this is to push the
backports
> > > through
> > > upstream -stable kernels. This stuff here is simple
enough
> > > that we can
> > > do it. Same could have been done for the fairly minimal
> > > fencing fixes
> > > for i915 (at least some of them, the ones in the
page-flip).
> > >
> > > Otherwise we'll end up with tons IM_NOT_BUGGY and
> > > IM_SLIGHTLY_LESS_BUGGY and
> > > IM_NOT_BUGGY_EXCEPT_THIS_BOTCHED_BACKPORT
> > > flags where no one at all knows what they mean,
usage between
> > > different drivers and different userspace is entirely
> > > inconsistent and
> > > they just all add to the confusion. They're just
bugs, lets
> > > treat them
> > > like that.
> > >
> > >
> > > It's not *quite* DRM_CAP_PRIME_SCANOUT_NOT_BUGGY - while the
relevant
> > > hardware allegedly supports it, nouveau/radeon/amdgpu don't
do scanout
> > > of GTT, so the lack of this cap indicates that there's no
point in
> > > trying to call addfb2.
> > >
> > >
> > > But calling addfb2 and it failing is not expensive, so this
is rather
> > > niche.
> > >
> > >
> > > In practice I can just restrict attempting to scanout of
imported
> > > buffers to i915, as that's the only driver that it'll work
on. By the
> > > time nouveau/radeon/amdgpu get patches to scanout of GTT the
fixes
> > > should be old enough that I don't need to care about unfixed
kernels.
> > >
> > So given that most discreet hardware won't ever be able to
scanout from
> > GTT (latency and iso requirements will be hard to meet), can't
we just
> > fix the case of the broken prime sharing when migrating to VRAM?
At least some nouveau and AMD devs seem to think that their hardware
is capable of doing it. Shrug.
Wow, wait a second. Recent AMD GPU can scanout from system memory,
that's true.
Even discrete GPUs, or only APUs?
Good question. The crux is that you need to match certain bandwith and
latency limitations or otherwise you get a flickering picture.
If I understood the documentation correctly that should even work with
dGPUs in theory, but nobody is testing/validating this.
Long story short I wouldn't try it without feedback from the hardware/DC
guys. They are the designated experts for this.
Regards,
Christian.
But you need to met quite a bunch of special allocation requirements to
do this.
When we are talking about sharing between AMD GPUs, (e.g. both exporter
and importer are AMD hardware) than that might work.
But I think it's unrealistic that an imported BO (created by an external
driver stack) will ever meet those requirements.
Indeed. Also, none of the GPUs supported by the radeon driver support this.
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