drm/i915: Turn on another required clock gating bit on gen6.

Unlike the previous one, I don't have known testcases it fixes.  I'd
rather not go through the same debug cycle on whatever testcases those
might be.

Signed-off-by: Eric Anholt <eric@anholt.net>
Cc: stable@kernel.org
Signed-off-by: Keith Packard <keithp@keithp.com>

2 files changed, 7 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index b807275ea739..a34e86630f26 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -3446,6 +3446,7 @@
 
 #define GEN6_UCGCTL2                            0x9404
 # define GEN6_RCPBUNIT_CLOCK_GATE_DISABLE               (1 << 12)
+# define GEN6_RCCUNIT_CLOCK_GATE_DISABLE                (1 << 11)
 
 #define GEN6_RPNSWREQ                           0xA008
 #define   GEN6_TURBO_DISABLE                    (1<<31)
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 2b2a7645cd0c..591eb0ed3110 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -8154,8 +8154,13 @@ static void gen6_init_clock_gating(struct drm_device *dev)
          * some amount of runtime in the Mesa "fire" demo, and Unigine
          * Sanctuary and Tropics, and apparently anything else with
          * alpha test or pixel discard.
+         *
+         * According to the spec, bit 11 (RCCUNIT) must also be set,
+         * but we didn't debug actual testcases to find it out.
          */
-        I915_WRITE(GEN6_UCGCTL2, GEN6_RCPBUNIT_CLOCK_GATE_DISABLE);
+        I915_WRITE(GEN6_UCGCTL2,
+                   GEN6_RCPBUNIT_CLOCK_GATE_DISABLE |
+                   GEN6_RCCUNIT_CLOCK_GATE_DISABLE);
 
         /*
          * According to the spec the following bits should be