drm/i915: Improve HiZ throughput on Cherryview.

Found by reading the HIZ_CHICKEN documentation.

Improves performance in a HiZ microbenchmark by around 50%.
Improves performance in OglZBuffer by around 18%.

Thanks to Chris Wilson for helping me figure out where to put this.
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -5202,6 +5202,9 @@ enum punit_power_well {
 #define COMMON_SLICE_CHICKEN2			0x7014
 # define GEN8_CSC2_SBE_VUE_CACHE_CONSERVATIVE	(1<<0)
 
+#define HIZ_CHICKEN				0x7018
+# define CHV_HZ_8X8_MODE_IN_1X			(1<<15)
+
 #define GEN7_L3SQCREG1				0xB010
 #define  VLV_B0_WA_L3SQCREG1_VALUE		0x00D30000
 

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -836,6 +836,9 @@ static int chv_init_workarounds(struct intel_engine_cs *ring)
 			  HDC_FORCE_NON_COHERENT |
 			  HDC_DONOT_FETCH_MEM_WHEN_MASKED);
 
+	/* Improve HiZ throughput on CHV. */
+	WA_SET_BIT_MASKED(HIZ_CHICKEN, CHV_HZ_8X8_MODE_IN_1X);
+
 	return 0;
 }