drm/i915: add TDL unit clock gating disable for VLV

Another required workaround for a potential hang:
WaDisableTDLUnitClockGating.

v2: only apply this to VLV, IVB doesn't need it anymore (Eugeni)

References: https://bugs.freedesktop.org/show_bug.cgi?id=50245
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -4038,6 +4038,7 @@
 
 #define GEN6_UCGCTL2				0x9404
 # define GEN7_VDSUNIT_CLOCK_GATE_DISABLE		(1 << 30)
+# define GEN7_TDLUNIT_CLOCK_GATE_DISABLE		(1 << 22)
 # define GEN6_RCZUNIT_CLOCK_GATE_DISABLE		(1 << 13)
 # define GEN6_RCPBUNIT_CLOCK_GATE_DISABLE		(1 << 12)
 # define GEN6_RCCUNIT_CLOCK_GATE_DISABLE		(1 << 11)

drivers/gpu/drm/i915/intel_pm.c

@@ -3512,6 +3512,7 @@ static void valleyview_init_clock_gating(struct drm_device *dev)
 	 */
 	I915_WRITE(GEN6_UCGCTL2,
 		   GEN7_VDSUNIT_CLOCK_GATE_DISABLE |
+		   GEN7_TDLUNIT_CLOCK_GATE_DISABLE |
 		   GEN6_RCZUNIT_CLOCK_GATE_DISABLE |
 		   GEN6_RCPBUNIT_CLOCK_GATE_DISABLE |
 		   GEN6_RCCUNIT_CLOCK_GATE_DISABLE);