Commit 7ffd7a68 authored Aug 06, 2014 by Ville Syrjälä Committed by Daniel Vetter Aug 06, 2014

drm: Always reject drm_vblank_get() after drm_vblank_off()



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().

When drm_vblank_get() encounters a >0 refcount and the vblank
interrupt is already disabled it will simply return -EINVAL.

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().

v2: Describe what drm_vblank_get() does to explain how
    a simple refcount bump manages to fix things (Daniel)

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

parent 21d70354

drivers/gpu/drm/drm_irq.c

+14 −0

Original line number	Diff line number	Diff line
		@@ -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));

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