drm/i915/gen9: Implement WaForceEnableNonCoherent

v2: Don't add WaHdcDisableFetchWhenMasked. Add stepping check for
WaForceEnableNonCoherent

Signed-off-by: Nick Hoath <nicholas.hoath@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -902,6 +902,17 @@ static int gen9_init_workarounds(struct intel_engine_cs *ring)
 				  GEN9_ENABLE_YV12_BUGFIX);
 	}
 
+	if (INTEL_REVID(dev) <= SKL_REVID_D0) {
+		/*
+		 *Use Force Non-Coherent whenever executing a 3D context. This
+		 * is a workaround for a possible hang in the unlikely event
+		 * a TLB invalidation occurs during a PSD flush.
+		 */
+		/* WaForceEnableNonCoherent:skl */
+		WA_SET_BIT_MASKED(HDC_CHICKEN0,
+				  HDC_FORCE_NON_COHERENT);
+	}
+
 	/* Wa4x4STCOptimizationDisable:skl */
 	WA_SET_BIT_MASKED(CACHE_MODE_1, GEN8_4x4_STC_OPTIMIZATION_DISABLE);