Re: [PATCH 1/3] drm: add debug print to update_vblank_count

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

On Thu, Jun 13, 2019 at 03:18:00PM +0300, Oleg Vasilev wrote:
> Since we are logging all vblank counter updates 30 lines below,
> it is also good to have some details whether and how vblank count
> difference is calculated.
> 
> Signed-off-by: Oleg Vasilev <oleg.vasilev@intel.com>
> ---
>  drivers/gpu/drm/drm_vblank.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 0d704bddb1a6..603ab105125d 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -241,12 +241,16 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
>  		 * on the difference in the timestamps and the
>  		 * frame/field duration.
>  		 */
> +
> +		DRM_DEBUG_VBL("crtc %u: Calculating number of vblanks."
> +			      " diff_ns = %lld, framedur_ns = %d)\n",
> +			      pipe, (long long) diff_ns, framedur_ns);

You can generally extract that info from the timestamps that already
get dumped, but I guess that is a bit of a hassle. So might as well
print the stuff the kernel already calculated for you.

The only downside is that lots of printks from the irq handler bogs
the machine down quite a bit. But these shouldn't be used outside of
short vbl debugging sessions anyway.

Pushed this one to drm-misc-next. Thanks for the patch.

> +
>  		diff = DIV_ROUND_CLOSEST_ULL(diff_ns, framedur_ns);
>  
>  		if (diff == 0 && in_vblank_irq)
> -			DRM_DEBUG_VBL("crtc %u: Redundant vblirq ignored."
> -				      " diff_ns = %lld, framedur_ns = %d)\n",
> -				      pipe, (long long) diff_ns, framedur_ns);
> +			DRM_DEBUG_VBL("crtc %u: Redundant vblirq ignored\n",
> +				      pipe);
>  	} else {
>  		/* some kind of default for drivers w/o accurate vbl timestamping */
>  		diff = in_vblank_irq ? 1 : 0;
> -- 
> 2.21.0
> 
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-- 
Ville Syrjälä
Intel
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