drm/i915/bdw: Sampler power bypass disable

BDW-A workaround.

BDW Bug #1899812
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -5009,6 +5009,7 @@
 
 #define HALF_SLICE_CHICKEN3		0xe184
 #define   GEN8_CENTROID_PIXEL_OPT_DIS	(1<<8)
+#define   GEN8_SAMPLER_POWER_BYPASS_DIS	(1<<1)
 
 #define G4X_AUD_VID_DID			(dev_priv->info->display_mmio_offset + 0x62020)
 #define INTEL_AUDIO_DEVCL		0x808629FB

drivers/gpu/drm/i915/intel_pm.c

@@ -5290,6 +5290,8 @@ static void gen8_init_clock_gating(struct drm_device *dev)
 	     "GEN8_CENTROID_PIXEL_OPT_DIS not be needed for production\n");
 	I915_WRITE(HALF_SLICE_CHICKEN3,
 		   _MASKED_BIT_ENABLE(GEN8_CENTROID_PIXEL_OPT_DIS));
+	I915_WRITE(HALF_SLICE_CHICKEN3,
+		   _MASKED_BIT_ENABLE(GEN8_SAMPLER_POWER_BYPASS_DIS));
 	I915_WRITE(GAMTARBMODE, _MASKED_BIT_ENABLE(ARB_MODE_BWGTLB_DISABLE));
 
 	/* WaSwitchSolVfFArbitrationPriority */