drm/i915/bdw: conservative SBE VUE cache mode

Hold vertex data in cache until last reference

BDW-A workaround
Signed-off-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -4133,6 +4133,8 @@
 /* GEN7 chicken */
 #define GEN7_COMMON_SLICE_CHICKEN1		0x7010
 # define GEN7_CSC1_RHWO_OPT_DISABLE_IN_RCC	((1<<10) | (1<<26))
+#define COMMON_SLICE_CHICKEN2			0x7014
+# define GEN8_CSC2_SBE_VUE_CACHE_CONSERVATIVE	(1<<0)
 
 #define GEN7_L3CNTLREG1				0xB01C
 #define  GEN7_WA_FOR_GEN7_L3_CONTROL			0x3C4FFF8C

drivers/gpu/drm/i915/intel_pm.c

@@ -5297,6 +5297,9 @@ static void gen8_init_clock_gating(struct drm_device *dev)
 	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);