[PATCH 1/2] drm: Fix off-by-one in vblank hardware counter wraparound handling

[Christian König]

Nice catch! Both patches in this series are Reviewed-by: Christian König 
<christian.koenig at amd.com>

On 26.05.2015 10:53, Michel Dänzer wrote:
> From: Michel Dänzer <michel.daenzer at amd.com>
>
> dev->max_vblank_count contains the largest value that can be represented
> by the hardware counter. When the hardware counter wraps around, we have
> to add that value + 1 to get the same value as if the hardware counter
> didn't wrap around.
>
> Signed-off-by: Michel Dänzer <michel.daenzer at amd.com>
> ---
>   drivers/gpu/drm/drm_irq.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> index c8a3447..f9634da 100644
> --- a/drivers/gpu/drm/drm_irq.c
> +++ b/drivers/gpu/drm/drm_irq.c
> @@ -100,7 +100,7 @@ static void drm_update_vblank_count(struct drm_device *dev, int crtc)
>   	/*
>   	 * Interrupts were disabled prior to this call, so deal with counter
>   	 * wrap if needed.
> -	 * NOTE!  It's possible we lost a full dev->max_vblank_count events
> +	 * NOTE!  It's possible we lost a full dev->max_vblank_count + 1 events
>   	 * here if the register is small or we had vblank interrupts off for
>   	 * a long time.
>   	 *
> @@ -117,7 +117,7 @@ static void drm_update_vblank_count(struct drm_device *dev, int crtc)
>   	/* Deal with counter wrap */
>   	diff = cur_vblank - vblank->last;
>   	if (cur_vblank < vblank->last) {
> -		diff += dev->max_vblank_count;
> +		diff += dev->max_vblank_count + 1;
>   
>   		DRM_DEBUG("last_vblank[%d]=0x%x, cur_vblank=0x%x => diff=0x%x\n",
>   			  crtc, vblank->last, cur_vblank, diff);