ddrm/i915/bdw: Disable centroid pixel perf optimization

BDW-A workaround

BDW Bug #1899532

v2: WARN on when not using preliminary HW support

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Jesse Barnes <jbarnes@virtuosugeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index b87945d5..ffd103a 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -5007,6 +5007,9 @@
 #define HSW_ROW_CHICKEN3		0xe49c
 #define  HSW_ROW_CHICKEN3_L3_GLOBAL_ATOMICS_DISABLE    (1 << 6)
 
+#define HALF_SLICE_CHICKEN3		0xe184
+#define   GEN8_CENTROID_PIXEL_OPT_DIS	(1<<8)
+
 #define G4X_AUD_VID_DID			(dev_priv->info->display_mmio_offset + 0x62020)
 #define INTEL_AUDIO_DEVCL		0x808629FB
 #define INTEL_AUDIO_DEVBLC		0x80862801