drm/i915/gen9: implement WaEnableSamplerGPGPUPreemptionSupport

WaEnableSamplerGPGPUPreemptionSupport fixes a problem
related to mid thread pre-emption.

Signed-off-by: Tim Gore <tim.gore@intel.com>
Reviewed-by: Dave Gordon <david.s.gordon@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1461077152-31899-1-git-send-email-tim.gore@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -7180,6 +7180,7 @@ enum skl_disp_power_wells {
 
 #define GEN9_HALF_SLICE_CHICKEN7	_MMIO(0xe194)
 #define   GEN9_ENABLE_YV12_BUGFIX	(1<<4)
+#define   GEN9_ENABLE_GPGPU_PREEMPTION	(1<<2)
 
 /* Audio */
 #define G4X_AUD_VID_DID			_MMIO(dev_priv->info.display_mmio_offset + 0x62020)

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -959,9 +959,10 @@ static int gen9_init_workarounds(struct intel_engine_cs *engine)
 	}
 
 	/* WaEnableYV12BugFixInHalfSliceChicken7:skl,bxt */
-	if (IS_SKL_REVID(dev, SKL_REVID_C0, REVID_FOREVER) || IS_BROXTON(dev))
-		WA_SET_BIT_MASKED(GEN9_HALF_SLICE_CHICKEN7,
-				  GEN9_ENABLE_YV12_BUGFIX);
+	/* WaEnableSamplerGPGPUPreemptionSupport:skl,bxt */
+	WA_SET_BIT_MASKED(GEN9_HALF_SLICE_CHICKEN7,
+			  GEN9_ENABLE_YV12_BUGFIX |
+			  GEN9_ENABLE_GPGPU_PREEMPTION);
 
 	/* Wa4x4STCOptimizationDisable:skl,bxt */
 	/* WaDisablePartialResolveInVc:skl,bxt */