[PATCH] drm/i915: fix errata for sync flush enable on 845G/830M

[Chris Wilson <chris@chris-wilson.co.uk>]

From: Zhenyu Wang <zhenyuw@linux.intel.com>

The sync flush enable mask on 845G and 830M is flipped.
So driver should invert it usage.

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_dma.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index f19ffe8..4b6c2f8 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -1356,6 +1356,7 @@ static int i915_load_modeset_init(struct drm_device *dev,
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	int fb_bar = IS_I9XX(dev) ? 2 : 0;
+	u32 instpm_val;
 	int ret = 0;
 
 	dev->mode_config.fb_base = pci_resource_start(dev->pdev, fb_bar) &
@@ -1432,9 +1433,14 @@ static int i915_load_modeset_init(struct drm_device *dev,
 
 	/*
 	 * Initialize the hardware status page IRQ location.
+	 * errata: on 845G and 830M, bit 21's polarity is reversed,
+	 * so the usage is inverted.
 	 */
-
-	I915_WRITE(INSTPM, (1 << 5) | (1 << 21));
+	if (IS_845G(dev) || IS_I830(dev))
+	    instpm_val = (1 << 5) | (0 << 21);
+	else
+	    instpm_val = (1 << 5) | (1 << 21);
+	I915_WRITE(INSTPM, instpm_val);
 
 	ret = intel_fbdev_init(dev);
 	if (ret)
-- 
1.7.1