Re: [PATCH] drm/nouveau: Fix pre-nv50 pageflip events (v4)

[Thierry Reding <thierry.reding@gmail.com>]

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On Tue, Nov 10, 2015 at 05:37:31PM +0100, Thierry Reding wrote:
> From: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> 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@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@nvidia.com>
> Date:   Wed Aug 12 17:00:31 2015 +0200
> 
>     drm/irq: Make pipe unsigned and name consistent
> 
> Triggering 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.
> 
> v2 (Mario Kleiner):
> - Fix function prototypes in drmP.h
> - Add missing vblank_put() for pageflip completion without
>   pageflip event.
> - Initialize sequence number for queued pageflip event to avoid
>   trouble in drm_handle_vblank_events().
> - Remove dead code and spelling fix.
> 
> v3 (Mario Kleiner):
> - Add a signed-off-by and cc stable tag per Ilja's advice.
> 
> v4 (Thierry Reding):
> - Fix kerneldoc typo, discovered by Michel Dänzer
> - Rearrange tags and changelog
> 
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=106431
> Cc: Thierry Reding <treding@nvidia.com>
> Cc: Mario Kleiner <mario.kleiner.de@gmail.com>
> Cc: Ben Skeggs <bskeggs@redhat.com>
> Cc: Ilia Mirkin <imirkin@alum.mit.edu>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Reviewed-by: Mario Kleiner <mario.kleiner.de@gmail.com>
> Cc: stable@vger.kernel.org # v4.3
> Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
>  drivers/gpu/drm/drm_irq.c                 | 54 ++++++++++++++++++++++++++++++-
>  drivers/gpu/drm/nouveau/nouveau_display.c | 19 ++++++-----
>  include/drm/drmP.h                        |  4 +++
>  3 files changed, 68 insertions(+), 9 deletions(-)

Hi Dave,

It'd be great if you could queue this up for fixes, since it gets rid of
a WARN_ON() that is triggered on a number of cards in v4.3. I realize
that this is a tad big for stable, but it's the right way to fix this.
If you'd prefer something smaller, I think we can fix the regression
using a one-line band-aid and then apply this one on top for v4.4.

Thierry

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