drm/i915: Change VLV WIZ hashing mode to 16x4

We set the WIZ hashing mode to 16x4 for all the other gen6+
platfotrms, so let's follow suit on VLV.

My VLV is AWOL currently so I didn't test this, but since the results
for all the other platforms agree that 16x4 is the fastest we might
assume the same holds for VLV.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Arun Siluvery <arun.siluvery@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -6229,6 +6229,17 @@ static void valleyview_init_clock_gating(struct drm_device *dev)
 	I915_WRITE(CACHE_MODE_1,
 		   _MASKED_BIT_ENABLE(PIXEL_SUBSPAN_COLLECT_OPT_DISABLE));
 
+	/*
+	 * BSpec recommends 8x4 when MSAA is used,
+	 * however in practice 16x4 seems fastest.
+	 *
+	 * Note that PS/WM thread counts depend on the WIZ hashing
+	 * disable bit, which we don't touch here, but it's good
+	 * to keep in mind (see 3DSTATE_PS and 3DSTATE_WM).
+	 */
+	I915_WRITE(GEN7_GT_MODE,
+		   _MASKED_FIELD(GEN6_WIZ_HASHING_MASK, GEN6_WIZ_HASHING_16x4));
+
 	/*
 	 * WaIncreaseL3CreditsForVLVB0:vlv
 	 * This is the hardware default actually.