drm/i915/bdw: Implement WaForceContextSaveRestoreNonCoherent

v2: Reorder defines (Ben)
v3: More bikesheds, this time re-ordering comments! (Chris)
Reviewed-by: NBen Widawsky <ben@bwidawsk.net>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
[danvet: Resolve conflict.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -5260,9 +5260,10 @@ enum skl_disp_power_wells {
 
 /* GEN8 chicken */
 #define HDC_CHICKEN0				0x7300
-#define  HDC_FORCE_NON_COHERENT			(1<<4)
-#define  HDC_DONOT_FETCH_MEM_WHEN_MASKED	(1<<11)
 #define  HDC_FENCE_DEST_SLM_DISABLE		(1<<14)
+#define  HDC_DONOT_FETCH_MEM_WHEN_MASKED	(1<<11)
+#define  HDC_FORCE_CONTEXT_SAVE_RESTORE_NON_COHERENT	(1<<5)
+#define  HDC_FORCE_NON_COHERENT			(1<<4)
 
 /* WaCatErrorRejectionIssue */
 #define GEN7_SQ_CHICKEN_MBCUNIT_CONFIG		0x9030

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -788,12 +788,14 @@ static int bdw_init_workarounds(struct intel_engine_cs *ring)
 	 * workaround for for a possible hang in the unlikely event a TLB
 	 * invalidation occurs during a PSD flush.
 	 */
-	/* WaForceEnableNonCoherent:bdw */
-	/* WaHdcDisableFetchWhenMasked:bdw */
-	/* WaDisableFenceDestinationToSLM:bdw (GT3 pre-production) */
 	WA_SET_BIT_MASKED(HDC_CHICKEN0,
+			  /* WaForceEnableNonCoherent:bdw */
 			  HDC_FORCE_NON_COHERENT |
+			  /* WaForceContextSaveRestoreNonCoherent:bdw */
+			  HDC_FORCE_CONTEXT_SAVE_RESTORE_NON_COHERENT |
+			  /* WaHdcDisableFetchWhenMasked:bdw */
 			  HDC_DONOT_FETCH_MEM_WHEN_MASKED |
+			  /* WaDisableFenceDestinationToSLM:bdw (pre-prod) */
 			  (IS_BDW_GT3(dev) ? HDC_FENCE_DEST_SLM_DISABLE : 0));
 
 	/* From the Haswell PRM, Command Reference: Registers, CACHE_MODE_0: