Re: [PATCH v2 3/4] drm: Refactor vblank sequence number comparison

["Michel Dänzer" <michel@daenzer.net>]

On 18/03/17 05:20 AM, Chris Wilson wrote:
> Move the repeated (a - b) <= (1 << 23) to its own function.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/drm_irq.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> index a164cf51d093..253505da57bd 100644
> --- a/drivers/gpu/drm/drm_irq.c
> +++ b/drivers/gpu/drm/drm_irq.c
> @@ -1492,6 +1492,11 @@ int drm_legacy_modeset_ctl(struct drm_device *dev, void *data,
>  	return 0;
>  }
>  
> +static inline bool vblank_passed(u32 seq, u32 ref)
> +{
> +	return (seq - ref) <= (1 << 23);
> +}

As a followup, maybe we could try changing this to

    return (s32)(seq - ref) >= 0;


> @@ -1542,7 +1547,7 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe,
>  				      vblwait->request.sequence);
>  
>  	e->event.sequence = vblwait->request.sequence;
> -	if ((seq - vblwait->request.sequence) <= (1 << 23)) {
> +	if (vblank_passed(seq, vblwait->request.sequence)) {
>  		drm_vblank_put(dev, pipe);
>  		send_vblank_event(dev, e, seq, &now);
>  		vblwait->reply.sequence = seq;
> @@ -1632,9 +1637,8 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
>  	}
>  
>  	if ((flags & _DRM_VBLANK_NEXTONMISS) &&
> -	    (seq - vblwait->request.sequence) <= (1 << 23)) {
> +	    vblank_passed(seq, vblwait->request.sequence))
>  		vblwait->request.sequence = seq + 1;
> -	}
>  
>  	if (flags & _DRM_VBLANK_EVENT) {
>  		/* must hold on to the vblank ref until the event fires
> @@ -1647,8 +1651,8 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
>  		DRM_DEBUG("waiting on vblank count %u, crtc %u\n",
>  			  vblwait->request.sequence, pipe);
>  		DRM_WAIT_ON(ret, vblank->queue, 3 * HZ,
> -			    (drm_vblank_count(dev, pipe) -
> -			     vblwait->request.sequence) <= (1 << 23) ||
> +			    vblank_passed(drm_vblank_count(dev, pipe),
> +					  vblwait->request.sequence) ||
>  			    !READ_ONCE(vblank->enabled));
>  	}
>  
> 

There's another instance in drm_handle_vblank_events.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer
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