drm/i915: Add support for GPU reset on gen6.

This has proven sufficient to recover from a hang of the GPU using the
gem_bad_blit test while at the KMS console then starting X.  When
attempting the same during an X session, the timer doesn't appear to
trigger.
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_drv.c

@@ -405,6 +405,14 @@ static int ironlake_do_reset(struct drm_device *dev, u8 flags)
 	return wait_for(I915_READ(MCHBAR_MIRROR_BASE + ILK_GDSR) & 0x1, 500);
 }
 
+static int gen6_do_reset(struct drm_device *dev, u8 flags)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	I915_WRITE(GEN6_GDRST, GEN6_GRDOM_FULL);
+	return wait_for((I915_READ(GEN6_GDRST) & GEN6_GRDOM_FULL) == 0, 500);
+}
+
 /**
  * i965_reset - reset chip after a hang
  * @dev: drm device to reset
@@ -439,6 +447,9 @@ int i915_reset(struct drm_device *dev, u8 flags)
 	if (get_seconds() - dev_priv->last_gpu_reset < 5) {
 		DRM_ERROR("GPU hanging too fast, declaring wedged!\n");
 	} else switch (INTEL_INFO(dev)->gen) {
+	case 6:
+		ret = gen6_do_reset(dev, flags);
+		break;
 	case 5:
 		ret = ironlake_do_reset(dev, flags);
 		break;

drivers/gpu/drm/i915/i915_reg.h

@@ -78,6 +78,12 @@
 #define  GRDOM_RENDER	(1<<2)
 #define  GRDOM_MEDIA	(3<<2)
 
+#define GEN6_GDRST	0x941c
+#define  GEN6_GRDOM_FULL		(1 << 0)
+#define  GEN6_GRDOM_RENDER		(1 << 1)
+#define  GEN6_GRDOM_MEDIA		(1 << 2)
+#define  GEN6_GRDOM_BLT			(1 << 3)
+
 /* VGA stuff */
 
 #define VGA_ST01_MDA 0x3ba