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

[poma]

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