[PATCH] drm/vblank: WARN_ON nested use of drm_vblank_on/off

[Daniel Vetter <daniel.vetter@ffwll.ch>]

We should never nest these since in theory kms drivers should know
when a pipe is on/off and call the corresponding enable/disable
functions for the vblank helper code only once. But for historical
reasons (the shared-with-ums version of this code in modeset_pre/post
needed to be able to cope with silly userspace that lost track of
things) we still have this bit of "robustness" around.

Enforce this with a WARN_ON, preparing to eventually rip out this
special handling.

Cc: Yogesh Mohan Marimuthu <yogesh.mohan.marimuthu@intel.com>
Cc: Gaurav K Singh <gaurav.k.singh@intel.com>
Cc: Michel Dänzer <michel.daenzer@amd.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
---
 drivers/gpu/drm/drm_irq.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index f9cc68fbd2a3..3819465abe22 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -1219,6 +1219,8 @@ void drm_vblank_off(struct drm_device *dev, int crtc)
 	vblank_disable_and_save(dev, crtc);
 	wake_up(&vblank->queue);
 
+	WARN_ON(vblank->inmodeset);
+
 	/*
 	 * Prevent subsequent drm_vblank_get() from re-enabling
 	 * the vblank interrupt by bumping the refcount.
@@ -1318,6 +1320,8 @@ void drm_vblank_on(struct drm_device *dev, int crtc)
 		return;
 
 	spin_lock_irqsave(&dev->vbl_lock, irqflags);
+	WARN_ON(!vblank->inmodeset);
+
 	/* Drop our private "prevent drm_vblank_get" refcount */
 	if (vblank->inmodeset) {
 		atomic_dec(&vblank->refcount);
-- 
2.1.4

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