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. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
