[PATCH 4/4] drm/i915: Fix GT_MODE default value

[Ben Widawsky <ben@bwidawsk.net>]

I can't even find how I figured this might be needed anymore. But sure
enough, the value I'm reading back on platforms doesn't match what the
docs recommends.

It seemed to fix Chris' GT1 in limited testing as well.

Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_reg.h | 3 +++
 drivers/gpu/drm/i915/intel_pm.c | 5 +++++
 2 files changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 37e62e0..4c1f461 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -531,6 +531,9 @@
 # define VS_TIMER_DISPATCH				(1 << 6)
 # define MI_FLUSH_ENABLE				(1 << 12)
 
+#define GEN6_GT_MODE	0x20d0
+#define   GEN6_GT_MODE_HI	(1 << 9)
+
 #define GFX_MODE	0x02520
 #define GFX_MODE_GEN7	0x0229c
 #define RING_MODE_GEN7(ring)	((ring)->mmio_base+0x29c)
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 8aafa45..e0574f9 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3446,6 +3446,11 @@ static void gen6_init_clock_gating(struct drm_device *dev)
 			   DISPPLANE_TRICKLE_FEED_DISABLE);
 		intel_flush_display_plane(dev_priv, pipe);
 	}
+
+	/* The default value should be 0x200 according to docs, but the two
+	 * platforms I checked have a 0 for this. (Maybe BIOS overrides?) */
+	I915_WRITE(GEN6_GT_MODE, _MASKED_BIT_DISABLE(0xffff));
+	I915_WRITE(GEN6_GT_MODE, _MASKED_BIT_ENABLE(GEN6_GT_MODE_HI));
 }
 
 static void gen7_setup_fixed_func_scheduler(struct drm_i915_private *dev_priv)
-- 
1.7.12.2