Re: [PATCH 4/5] drm: Allow reenabling of vblank interrupts even if refcount>0

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Fri, 21 Feb 2014 21:03:34 +0200
ville.syrjala@linux.intel.com wrote:

> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> If someone holds a vblank reference across the modeset, and after/during
> the modeset someone tries to grab a vblank reference, the current code
> won't re-enable the vblank interrupts. That's not good, so instead allow
> the driver to choose whether drm_vblank_get() should always enable the
> interrupts regardless of the refcount.
> 
> Combined with the drm_vblank_off/drm_vblank_on reject mechanism, this
> can also be used to allow drivers to use vblank interrupts during
> modeset, whether or not someone is currently holding a vblank reference.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/drm_irq.c | 3 ++-
>  include/drm/drmP.h        | 6 ++++++
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> index 6e5d820..d613b6f 100644
> --- a/drivers/gpu/drm/drm_irq.c
> +++ b/drivers/gpu/drm/drm_irq.c
> @@ -897,7 +897,8 @@ int drm_vblank_get(struct drm_device *dev, int crtc)
>  	}
>  
>  	/* Going from 0->1 means we have to enable interrupts again */
> -	if (atomic_add_return(1, &dev->vblank[crtc].refcount) == 1) {
> +	if (atomic_add_return(1, &dev->vblank[crtc].refcount) == 1 ||
> +	    dev->vblank_always_enable_on_get) {
>  		spin_lock(&dev->vblank_time_lock);
>  		if (!dev->vblank[crtc].enabled) {
>  			/* Enable vblank irqs under vblank_time_lock protection.
> diff --git a/include/drm/drmP.h b/include/drm/drmP.h
> index ee40483..3eca0ee 100644
> --- a/include/drm/drmP.h
> +++ b/include/drm/drmP.h
> @@ -1156,6 +1156,12 @@ struct drm_device {
>  	 */
>  	bool vblank_disable_allowed;
>  
> +	/*
> +	 * Should a non-rejected drm_vblank_get() always enable the
> +	 * vblank interrupt regardless of the current refcount?
> +	 */
> +	bool vblank_always_enable_on_get;
> +
>  	/* array of size num_crtcs */
>  	struct drm_vblank_crtc *vblank;
>  

This seems like the sort of thing it would be good to have a test
for... I'm surprised we haven't hit it yet.  But in looking at the code
I don't see where we'd re-enable things properly in this situation, so
I guess it's a real bug.

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>

-- 
Jesse Barnes, Intel Open Source Technology Center
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