[Intel-gfx] [PATCH 1/9] drm: Always reject drm_vblank_get() after drm_vblank_off()

[Daniel Vetter]

On Mon, May 26, 2014 at 02:46:24PM +0300, ville.syrjala at linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Make sure drm_vblank_get() never succeeds when called between
> drm_vblank_off() and drm_vblank_on(). Borrow a trick from the
> old drm_vblank_{pre,post}_modeset() functions and just bump
> the refcount in drm_vblank_off() and drop it in drm_vblank_on().
> 
> Hopefully the use of inmodeset won't conflict badly with
> drm_vblank_{pre,post}_modeset().
> 
> For i915 there's a window between drm_vblank_off() and marking the
> crtc as inactive where the current code still allows drm_vblank_get().
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

Afaics we never check anywhere for inmodeset in drm_vblank_get, so how
does this work?
-Daniel

> ---
>  drivers/gpu/drm/drm_irq.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> index b565372..7b1e08c 100644
> --- a/drivers/gpu/drm/drm_irq.c
> +++ b/drivers/gpu/drm/drm_irq.c
> @@ -1039,6 +1039,15 @@ void drm_vblank_off(struct drm_device *dev, int crtc)
>  	}
>  	spin_unlock(&dev->event_lock);
>  
> +	/*
> +	 * Prevent subsequent drm_vblank_get() from re-enabling
> +	 * the vblank interrupt by bumping the refcount.
> +	 */
> +	if (!dev->vblank[crtc].inmodeset) {
> +		atomic_inc(&dev->vblank[crtc].refcount);
> +		dev->vblank[crtc].inmodeset = 1;
> +	}
> +
>  	spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
>  }
>  EXPORT_SYMBOL(drm_vblank_off);
> @@ -1079,6 +1088,11 @@ void drm_vblank_on(struct drm_device *dev, int crtc)
>  	unsigned long irqflags;
>  
>  	spin_lock_irqsave(&dev->vbl_lock, irqflags);
> +	/* Drop our private "prevent drm_vblank_get" refcount */
> +	if (dev->vblank[crtc].inmodeset) {
> +		atomic_dec(&dev->vblank[crtc].refcount);
> +		dev->vblank[crtc].inmodeset = 0;
> +	}
>  	/* re-enable interrupts if there's are users left */
>  	if (atomic_read(&dev->vblank[crtc].refcount) != 0)
>  		WARN_ON(drm_vblank_enable(dev, crtc));
> -- 
> 1.8.5.5
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch