[PATCH 2/2] drm: WARN if drm_handle_vblank is called errornously

[Daniel Vetter]

KMS drivers are in full control of their irq and vblank handling, if
they get a vblank interrupt before drm_vblank_init or after
drm_vblank_cleanup that's just a driver bug.

For ums driver there's only r128 and radeon which support vblank, and
they call drm_vblank_init in their driver load functions. Which again
means that userspace can do whatever it wants with interrupt, vblank
structures will always be there.

So this should never happen, let's catch driver issues with a WARN_ON.
Motivated by some discussions with Imre.

v2: Use WARN_ON_ONCE as suggested by Imre.

Cc: Imre Deak <imre.deak at intel.com>
Reviewed-by: Imre Deak <imre.deak at intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
---
 drivers/gpu/drm/drm_irq.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 3c18e522cc3b..dbece03979f3 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -1682,7 +1682,7 @@ bool drm_handle_vblank(struct drm_device *dev, int crtc)
 	struct timeval tvblank;
 	unsigned long irqflags;
 
-	if (!dev->num_crtcs)
+	if (WARN_ON_ONCE(!dev->num_crtcs))
 		return false;
 
 	if (WARN_ON(crtc >= dev->num_crtcs))
-- 
1.9.3