drm/i915: Set the required VFMUNIT clock gating disable on Ironlake.

It's required by the specs, but we don't know why.  Let's not find out
why.
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_reg.h

@@ -2471,6 +2471,9 @@
 # define MARIUNIT_CLOCK_GATE_DISABLE		(1 << 18)
 # define SVSMUNIT_CLOCK_GATE_DISABLE		(1 << 1)
 
+#define PCH_3DCGDIS1		0x46024
+# define VFMUNIT_CLOCK_GATE_DISABLE		(1 << 11)
+
 #define FDI_PLL_FREQ_CTL        0x46030
 #define  FDI_PLL_FREQ_CHANGE_REQUEST    (1<<24)
 #define  FDI_PLL_FREQ_LOCK_LIMIT_MASK   0xfff00

drivers/gpu/drm/i915/intel_display.c

@@ -5825,6 +5825,8 @@ void intel_init_clock_gating(struct drm_device *dev)
 			I915_WRITE(PCH_3DCGDIS0,
 				   MARIUNIT_CLOCK_GATE_DISABLE |
 				   SVSMUNIT_CLOCK_GATE_DISABLE);
+			I915_WRITE(PCH_3DCGDIS1,
+				   VFMUNIT_CLOCK_GATE_DISABLE);
 		}
 
 		I915_WRITE(PCH_DSPCLK_GATE_D, dspclk_gate);