Re: [Intel-gfx] [PATCH v2 02/21] drm: Evaluate struct drm_device.vblank_disable_immediate on each use

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

On Wed, Jan 15, 2020 at 01:16:33PM +0100, Thomas Zimmermann wrote:
> VBLANK interrupts can be disabled immediately or with a delay, where the
> latter is the default. The former option can be selected by setting
> get_vblank_timestamp, and enabling vblank_disable_immediate in struct
> drm_device.
> 
> The setup is only evaluated once when DRM initializes VBLANKs. Evaluating
> the settings on each use of vblank_disable_immediate will allow for easy
> integration of CRTC VBLANK functions.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---
>  drivers/gpu/drm/drm_vblank.c | 31 ++++++++++++++-----------------
>  1 file changed, 14 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 3f1dd54cc8bb..abb085c67d82 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -481,19 +481,6 @@ int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs)
>  
>  	DRM_INFO("Supports vblank timestamp caching Rev 2 (21.10.2013).\n");
>  
> -	/* Driver specific high-precision vblank timestamping supported? */
> -	if (dev->driver->get_vblank_timestamp)
> -		DRM_INFO("Driver supports precise vblank timestamp query.\n");
> -	else
> -		DRM_INFO("No driver support for vblank timestamp query.\n");
> -
> -	/* Must have precise timestamping for reliable vblank instant disable */
> -	if (dev->vblank_disable_immediate && !dev->driver->get_vblank_timestamp) {
> -		dev->vblank_disable_immediate = false;
> -		DRM_INFO("Setting vblank_disable_immediate to false because "
> -			 "get_vblank_timestamp == NULL\n");
> -	}

Which drivers are so broken they set vblank_disable_immediate to true
without having the vfunc specified? IMO this code should just go away
(or converted to a WARN).

> -
>  	return 0;
>  
>  err:
> @@ -1070,6 +1057,15 @@ int drm_crtc_vblank_get(struct drm_crtc *crtc)
>  }
>  EXPORT_SYMBOL(drm_crtc_vblank_get);
>  
> +static bool __vblank_disable_immediate(struct drm_device *dev, unsigned int pipe)
> +{
> +	if (!dev->vblank_disable_immediate)
> +		return false;
> +	if (!dev->driver->get_vblank_timestamp)
> +		return false;
> +	return true;
> +}
> +
>  static void drm_vblank_put(struct drm_device *dev, unsigned int pipe)
>  {
>  	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> @@ -1086,7 +1082,7 @@ static void drm_vblank_put(struct drm_device *dev, unsigned int pipe)
>  			return;
>  		else if (drm_vblank_offdelay < 0)
>  			vblank_disable_fn(&vblank->disable_timer);
> -		else if (!dev->vblank_disable_immediate)
> +		else if (__vblank_disable_immediate(dev, pipe))
>  			mod_timer(&vblank->disable_timer,
>  				  jiffies + ((drm_vblank_offdelay * HZ)/1000));
>  	}
> @@ -1663,7 +1659,7 @@ int drm_wait_vblank_ioctl(struct drm_device *dev, void *data,
>  	/* If the counter is currently enabled and accurate, short-circuit
>  	 * queries to return the cached timestamp of the last vblank.
>  	 */
> -	if (dev->vblank_disable_immediate &&
> +	if (__vblank_disable_immediate(dev, pipe) &&
>  	    drm_wait_vblank_is_query(vblwait) &&
>  	    READ_ONCE(vblank->enabled)) {
>  		drm_wait_vblank_reply(dev, pipe, &vblwait->reply);
> @@ -1820,7 +1816,7 @@ bool drm_handle_vblank(struct drm_device *dev, unsigned int pipe)
>  	 * been signaled. The disable has to be last (after
>  	 * drm_handle_vblank_events) so that the timestamp is always accurate.
>  	 */
> -	disable_irq = (dev->vblank_disable_immediate &&
> +	disable_irq = (__vblank_disable_immediate(dev, pipe) &&
>  		       drm_vblank_offdelay > 0 &&
>  		       !atomic_read(&vblank->refcount));
>  
> @@ -1893,7 +1889,8 @@ int drm_crtc_get_sequence_ioctl(struct drm_device *dev, void *data,
>  	pipe = drm_crtc_index(crtc);
>  
>  	vblank = &dev->vblank[pipe];
> -	vblank_enabled = dev->vblank_disable_immediate && READ_ONCE(vblank->enabled);
> +	vblank_enabled = __vblank_disable_immediate(dev, pipe) &&
> +			 READ_ONCE(vblank->enabled);
>  
>  	if (!vblank_enabled) {
>  		ret = drm_crtc_vblank_get(crtc);
> -- 
> 2.24.1
> 
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-- 
Ville Syrjälä
Intel