drm/i915/bdw: Force all Data Cache Data Port access to be Non-Coherent

I stumbled on to some unimplemented errata. To be honest, I am not
really sure of the impact, just that the docs say to do.

No w/a name for this one.

v2: v1 was a stale thing which should have never seen the light of day.
(Haihao)

Cc: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -4167,6 +4167,10 @@
 #define GEN7_L3SQCREG4				0xb034
 #define  L3SQ_URB_READ_CAM_MATCH_DISABLE	(1<<27)
 
+/* GEN8 chicken */
+#define HDC_CHICKEN0				0x7300
+#define  HDC_FORCE_NON_COHERENT			(1<<4)
+
 /* WaCatErrorRejectionIssue */
 #define GEN7_SQ_CHICKEN_MBCUNIT_CONFIG		0x9030
 #define  GEN7_SQ_CHICKEN_MBCUNIT_SQINTMOB	(1<<11)

drivers/gpu/drm/i915/intel_pm.c

@@ -5269,6 +5269,14 @@ static void gen8_init_clock_gating(struct drm_device *dev)
 			   I915_READ(CHICKEN_PIPESL_1(i) |
 				     DPRS_MASK_VBLANK_SRD));
 	}
+
+	/* Use Force Non-Coherent whenever executing a 3D context. This is a
+	 * workaround for for a possible hang in the unlikely event a TLB
+	 * invalidation occurs during a PSD flush.
+	 */
+	I915_WRITE(HDC_CHICKEN0,
+		   I915_READ(HDC_CHICKEN0) |
+		   _MASKED_BIT_ENABLE(HDC_FORCE_NON_COHERENT));
 }
 
 static void haswell_init_clock_gating(struct drm_device *dev)