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

[Benjamin Gaignard]

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.");
>
>         spin_lock_irqsave(&dev->vblank_time_lock, flags);
>
> --
> 2.13.6
>
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