On Wed, Apr 5, 2017 at 4:27 PM, Daniel Vetter <daniel@xxxxxxxx> wrote:
On Wed, Apr 05, 2017 at 12:20:46AM +0000, Christopher James Halse Rogers wrote:On Tue, Apr 4, 2017 at 9:53 PM Daniel Vetter <daniel@xxxxxxxx> wrote: > On Tue, Apr 4, 2017 at 12:43 PM, Lucas Stach <l.stach@xxxxxxxxxxxxxx> > 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."I'll only run on i915" sounds like a rather risky assumption. You're sure no one will install ubuntu on e.g. rasperry with Eric's shiny new pl111 driver? I really think that if you want to rely on this, backporting the fixes is perfectly fine.
Oh, no! I mean *check* that I'm running on i915, and only use the no-copy path if I am.
Backporting the patches would indeed be sensible. I guess I should have CC: stable'd at the time.
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