drm/i915: gen7: work around a system hang on IVB

This adds the workaround for WaCatErrorRejectionIssue which could result
in a system hang.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=41353
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=44610
Tested-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

drivers/gpu/drm/i915/i915_reg.h

@@ -3035,6 +3035,10 @@
 #define GEN7_L3_CHICKEN_MODE_REGISTER		0xB030
 #define  GEN7_WA_L3_CHICKEN_MODE				0x20000000
 
+/* WaCatErrorRejectionIssue */
+#define GEN7_SQ_CHICKEN_MBCUNIT_CONFIG		0x9030
+#define  GEN7_SQ_CHICKEN_MBCUNIT_SQINTMOB	(1<<11)
+
 /* PCH */
 
 /* south display engine interrupt */

drivers/gpu/drm/i915/intel_display.c

@@ -8478,6 +8478,11 @@ static void ivybridge_init_clock_gating(struct drm_device *dev)
 	I915_WRITE(GEN7_L3_CHICKEN_MODE_REGISTER,
 			GEN7_WA_L3_CHICKEN_MODE);
 
+	/* This is required by WaCatErrorRejectionIssue */
+	I915_WRITE(GEN7_SQ_CHICKEN_MBCUNIT_CONFIG,
+			I915_READ(GEN7_SQ_CHICKEN_MBCUNIT_CONFIG) |
+			GEN7_SQ_CHICKEN_MBCUNIT_SQINTMOB);
+
 	for_each_pipe(pipe) {
 		I915_WRITE(DSPCNTR(pipe),
 			   I915_READ(DSPCNTR(pipe)) |