commit e1a6fcee467556a7e955fe1f7ccc134dd2f974e7
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Tue Jan 6 10:21:24 2009 -0800

    drm/i915: set vblank enabled flag correctly across IRQ install/uninstall
    
    In the absence of kernel mode setting, many drivers disable IRQs across VT
    switch.  The core DRM vblank code is missing a check for this case however;
    even after IRQ disable, the vblank code will still have the vblank_enabled
    flag set, so unless we track the fact that they're disabled at IRQ uninstall
    time, when we VT switch back in we won't actually re-enable them, which means
    any apps waiting on vblank before the switch will hang.
    
    This patch does that and also adds a sanity check to the wait condition to
    look for the irq_enabled flag in general, as well as adding a wakeup to the
    IRQ uninstall path.
    
    Fixes fdo bug #18879 with compiz hangs at VT switch.
    
    Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
    Signed-off-by: Eric Anholt <eric@anholt.net>

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 1e787f8..e2f5d23 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -259,7 +259,8 @@ EXPORT_SYMBOL(drm_irq_install);
  */
 int drm_irq_uninstall(struct drm_device * dev)
 {
-	int irq_enabled;
+	unsigned long irqflags;
+	int irq_enabled, i;
 
 	if (!drm_core_check_feature(dev, DRIVER_HAVE_IRQ))
 		return -EINVAL;
@@ -269,6 +270,16 @@ int drm_irq_uninstall(struct drm_device * dev)
 	dev->irq_enabled = 0;
 	mutex_unlock(&dev->struct_mutex);
 
+	/*
+	 * Wake up any waiters so they don't hang.
+	 */
+	spin_lock_irqsave(&dev->vbl_lock, irqflags);
+	for (i = 0; i < dev->num_crtcs; i++) {
+		DRM_WAKEUP(&dev->vbl_queue[i]);
+		dev->vblank_enabled[i] = 0;
+	}
+	spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
+
 	if (!irq_enabled)
 		return -EINVAL;
 
@@ -617,8 +628,9 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
 		DRM_DEBUG("waiting on vblank count %d, crtc %d\n",
 			  vblwait->request.sequence, crtc);
 		DRM_WAIT_ON(ret, dev->vbl_queue[crtc], 3 * DRM_HZ,
-			    ((drm_vblank_count(dev, crtc)
-			      - vblwait->request.sequence) <= (1 << 23)));
+			    (((drm_vblank_count(dev, crtc) -
+			       vblwait->request.sequence) <= (1 << 23)) ||
+			     !dev->irq_enabled));
 
 		if (ret != -EINTR) {
 			struct timeval now;