[PATCH 4/6] drm: Fix treatment of drm_vblank_offdelay in drm_vblank_on()

[Daniel Vetter]

On Mon, Feb 08, 2016 at 02:13:27AM +0100, Mario Kleiner wrote:
> drm_vblank_offdelay can have three different types of values:
> 
> < 0 is to be always treated the same as dev->vblank_disable_immediate
> = 0 is to be treated as "never disable vblanks"
> > 0 is to be treated as disable immediate if kms driver wants it
>     that way via dev->vblank_disable_immediate. Otherwise it is
>     a disable timeout in msecs.
> 
> This got broken in Linux 3.18+ for the implementation of
> drm_vblank_on. If the user specified a value of zero which should
> always reenable vblank irqs in this function, a kms driver could
> override the users choice by setting vblank_disable_immediate
> to true. This patch fixes the regression and keeps the user in
> control.
> 
> Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
> Cc: <stable at vger.kernel.org> # 3.18+
> Cc: michel at daenzer.net
> Cc: vbabka at suse.cz
> Cc: ville.syrjala at linux.intel.com
> Cc: daniel.vetter at ffwll.ch
> Cc: dri-devel at lists.freedesktop.org
> Cc: alexander.deucher at amd.com
> Cc: christian.koenig 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 5c27ad3..fb17c45 100644
> --- a/drivers/gpu/drm/drm_irq.c
> +++ b/drivers/gpu/drm/drm_irq.c
> @@ -1492,8 +1492,8 @@ void drm_vblank_on(struct drm_device *dev, unsigned int pipe)
>  	 * re-enable interrupts if there are users left, or the
>  	 * user wishes vblank interrupts to be enabled all the time.
>  	 */
> -	if (atomic_read(&vblank->refcount) != 0 ||
> -	    (!dev->vblank_disable_immediate && drm_vblank_offdelay == 0))
> +	if (atomic_read(&vblank->refcount) != 0 || drm_vblank_offdelay == 0 ||
> +	    (!dev->vblank_disable_immediate && drm_vblank_offdelay > 0))

Hm, shouldn't we change this to only enable the vblank irq if we need it,
i.e. offdelay == 0? For delayed disabling there's kinda no need to enable
it superflously after a modeset, if userspace didn't yet ask for vblank
timestamps. But then is was specifically added by Ville in cd19e52aee922,
so I guess someone really wants this.

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

>  		WARN_ON(drm_vblank_enable(dev, pipe));
>  	spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
>  }
> -- 
> 1.9.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch