Re: [PATCH] drm/atomic-helper: Bump vblank timeout to 100 ms

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Apr 30, 2019 at 11:37:46AM +0200, Linus Walleij wrote:
> The 50 ms default timeout waiting for vblanks is too small
> for the first vblank from the ST-Ericsson MCDE display
> controller over DSI. Presumably this is because the DSI
> display is command-mode only and the state machine will
> take some time setting up its state for the first display
> update, and we hit a timeout. 100 ms makes it pass without
> problems.
> 
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
> After a quite prolonged hunting for the cause of missed
> vblanks in the MCDE driver I finally realized it timed
> out because it was simply taking some time on the first
> vblank. 50 ms makes sense on 60Hz monitors for sure,
> but an embedded DSI state machine can be slow, as it
> turns out.
> 
> Tell me if this should be a per-driver variable and I
> will think of something.
> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 40ac19848034..f0aa7b195d79 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1424,7 +1424,7 @@ drm_atomic_helper_wait_for_vblanks(struct drm_device *dev,
>  		ret = wait_event_timeout(dev->vblank[i].queue,
>  				old_state->crtcs[i].last_vblank_count !=
>  					drm_crtc_vblank_count(crtc),
> -				msecs_to_jiffies(50));
> +				msecs_to_jiffies(100));

50ms is pretty tight for 24Hz as well. I suppose we could make this
depend on the expected frame/field duration, but it's generally
indicative of a programming error of some sort, so as long as it's
long enough I think we're good.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

>  
>  		WARN(!ret, "[CRTC:%d:%s] vblank wait timed out\n",
>  		     crtc->base.id, crtc->name);
> -- 
> 2.20.1

-- 
Ville Syrjälä
Intel
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