drm/i915/bdw: conservative SBE VUE cache mode

Hold vertex data in cache until last reference

BDW-A workaround

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 5dceb56..ccd1b88 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -5297,6 +5297,9 @@
 	I915_WRITE(_3D_CHICKEN3,
 		   _3D_CHICKEN_SDE_LIMIT_FIFO_POLY_DEPTH(2));
 
+	I915_WRITE(COMMON_SLICE_CHICKEN2,
+		   _MASKED_BIT_ENABLE(GEN8_CSC2_SBE_VUE_CACHE_CONSERVATIVE));
+
 	/* WaSwitchSolVfFArbitrationPriority */
 	I915_WRITE(GAM_ECOCHK, I915_READ(GAM_ECOCHK) | HSW_ECOCHK_ARB_PRIO_SOL);