[PATCH] drm/vblank: Tune drm_crtc_accurate_vblank_count() WARN down to a debug

[Benjamin Gaignard]

2017-10-30 10:19 GMT+01:00 Daniel Vetter <daniel at ffwll.ch>:
> On Tue, Oct 24, 2017 at 11:01:32AM +0200, Benjamin Gaignard wrote:
>> 2017-10-23 17:25 GMT+02:00 Ville Syrjala <ville.syrjala at linux.intel.com>:
>> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
>> >
>> > Since commit 632c6e4edef1 ("drm/vblank: Fix flip event vblank count")
>> > even drivers that don't implement accurate vblank timestamps will end
>> > up using drm_crtc_accurate_vblank_count(). That leads to a WARN every
>> > time drm_crtc_arm_vblank_event() gets called. The could be as often
>> > as every frame for each active crtc.
>> >
>> > Considering drm_crtc_accurate_vblank_count() is never any worse than
>> > the drm_vblank_count() we used previously, let's just skip the WARN
>> > unless DRM_UT_VBL is enabled. That way people won't be bothered by
>> > this unless they're debugging vblank code. And let's also change it
>> > to WARN_ONCE() so that even when you're debugging vblank code you
>> > won't get drowned by constant WARNs.
>> >
>> > Cc: stable at vger.kernel.org
>> > Cc: Daniel Vetter <daniel at ffwll.ch>
>> > Cc: "Szyprowski, Marek" <m.szyprowski at samsung.com>
>> > Cc: Andrzej Hajda <a.hajda at samsung.com>
>> > Reported-by: Andrzej Hajda <a.hajda at samsung.com>
>> > Fixes: 632c6e4edef1 ("drm/vblank: Fix flip event vblank count")
>> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
>>
>> I have tested it on sti and stm driver, it fix the problem, thanks.
>>
>> Acked-by: Benjamin Gaignard <benjamin.gaignard at linaro.org>
>>
>> > ---
>> >  drivers/gpu/drm/drm_vblank.c | 4 ++--
>> >  1 file changed, 2 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
>> > index 13722c373a6a..c81c297995c6 100644
>> > --- a/drivers/gpu/drm/drm_vblank.c
>> > +++ b/drivers/gpu/drm/drm_vblank.c
>> > @@ -299,8 +299,8 @@ u32 drm_crtc_accurate_vblank_count(struct drm_crtc *crtc)
>> >         u32 vblank;
>> >         unsigned long flags;
>> >
>> > -       WARN(!dev->driver->get_vblank_timestamp,
>> > -            "This function requires support for accurate vblank timestamps.");
>> > +       WARN_ONCE(drm_debug & DRM_UT_VBL && !dev->driver->get_vblank_timestamp,
>> > +                 "This function requires support for accurate vblank timestamps.");
>
> Somewhat a bikeshed, but if we e.g. enable debugging in a CI or piglit
> run, then this could change the results. I'd go with a if ()
> DRM_DEBUG_VBLANK. Either way:
>
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>

Does something is missing to merge this fix in drm-misc ?
Without it I got warning at each frame.

Benjamin

>> >
>> >         spin_lock_irqsave(&dev->vblank_time_lock, flags);
>> >
>> > --
>> > 2.13.6
>> >
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>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch