From 63fd6f284ddd1096d34b39941683ae244c1e01fc Mon Sep 17 00:00:00 2001
From: Zou Nan hai <nanhai.zou@intel.com>
Date: Mon, 3 Mar 2008 14:49:49 +0800
Subject:   [i915] 2D driver may reset Frame count value, this may lead driver 
  to leap it's vblank count a huge value.   This will stall some applications
 that switch video mode if vblank_mode is set to a non zero value in drirc.

---
 shared-core/i915_irq.c | 7 +++++++
 1 file changed, 7 insertions(+)

(limited to 'shared-core')

diff --git a/shared-core/i915_irq.c b/shared-core/i915_irq.c
index fd08b6e8..126f0379 100644
--- a/shared-core/i915_irq.c
+++ b/shared-core/i915_irq.c
@@ -406,6 +406,13 @@ u32 i915_get_vblank_counter(struct drm_device *dev, int plane)
 	if (i915_in_vblank(dev, pipe))
 		count++;
 #endif
+	/* count may be reset by other driver(e.g. 2D driver), 
+	   we have no way to know if it is wrapped or resetted 
+	   when count is zero. do a rough guess.
+	*/
+	if (count == 0 && dev->last_vblank[pipe] < dev->max_vblank_count/2)
+		dev->last_vblank[pipe] = 0; 
+	
 	return count;
 }
 
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