drm/i915/bxt: add WaDisableMaskBasedCammingInRCC workaround

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Nick Hoath <nicholas.hoath@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index abe062a..e23cbdc 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -966,6 +966,15 @@
 	WA_CLR_BIT_MASKED(GEN9_HALF_SLICE_CHICKEN5,
 			  GEN9_CCS_TLB_PREFETCH_ENABLE);
 
+	/*
+	 * FIXME: don't apply the following on BXT for stepping C. On BXT A0
+	 * the flag reads back as 0.
+	 */
+	/* WaDisableMaskBasedCammingInRCC:bxtA */
+	if (IS_BROXTON(dev))
+		WA_SET_BIT_MASKED(SLICE_ECO_CHICKEN0,
+				  PIXEL_MASK_CAMMING_DISABLE);
+
 	return 0;
 }