[PATCH] drm/nouveau: Fix pre-nv50 pageflip events

[Daniel Vetter]

On Tue, Dec 01, 2015 at 04:08:16PM +0100, poma wrote:
> On Mon, Nov 16, 2015 at 4:11 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
> > On Mon, Nov 02, 2015 at 04:45:00PM +0900, Michel Dänzer wrote:
> >> On 31.10.2015 06:55, Daniel Vetter wrote:
> >> > Apparently pre-nv50 pageflip events happen before the actual vblank
> >> > period. Therefore that functionality got semi-disabled in
> >> >
> >> > commit af4870e406126b7ac0ae7c7ce5751f25ebe60f28
> >> > Author: Mario Kleiner <mario.kleiner.de at gmail.com>
> >> > Date:   Tue May 13 00:42:08 2014 +0200
> >> >
> >> >     drm/nouveau/kms/nv04-nv40: fix pageflip events via special case.
> >> >
> >> > Unfortunately that hack got uprooted in
> >> >
> >> > commit cc1ef118fc099295ae6aabbacc8af94d8d8885eb
> >> > Author: Thierry Reding <treding at nvidia.com>
> >> > Date:   Wed Aug 12 17:00:31 2015 +0200
> >> >
> >> >     drm/irq: Make pipe unsigned and name consistent
> >> >
> >> > Trigering a warning when trying to sample the vblank timestamp for a
> >> > non-existing pipe. There's a few ways to fix this:
> >> >
> >> > - Open-code the old behaviour, which just enshrines this slight
> >> >   breakage of the userspace ABI.
> >> >
> >> > - Revert Mario's commit and again inflict broken timestamps, again not
> >> >   pretty.
> >> >
> >> > - Fix this for real by delaying the pageflip TS until the next vblank
> >> >   interrupt, thereby making it accurate.
> >> >
> >> > This patch implements the third option. Since having a page flip
> >> > interrupt that happens when the pageflip gets armed and not when it
> >> > completes in the next vblank seems to be fairly common (older i915 hw
> >> > works very similarly) create a new helper to arm vblank events for
> >> > such drivers.
> >>
> >> What happens when the page flip interrupt arrives during a vertical
> >> blank period?  Presumably the userspace event will be deferred until the
> >> next vertical blank period, but the flip might already take effect in
> >> the current one.
> >
> > Hm yeah there's a tiny race if your update handler for the pageflip can
> > race with your vblank handler. That's impossible here since it's all done
> > from the same hw irq hanlder, and since that is single-threaded there
> > shouldn't be a problem, as long as vblank handling are pageflip are
> > ordered correctly.
> >
> > Might be worth a note in the kerneldoc though that this function isn't
> > perfectly foolproof.
> > -Daniel
> 
> 
> Is there any updates in this respect?
> 
> drm-nouveau-Fix-pre-nv50-pageflip-events-v4.patch
> https://patchwork.kernel.org/patch/7591531
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=106431
> Reported:     2015-10-21

Ben Skeggs asleep probably. Dave, can you pls pick this up?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch