drm/i915: Implement WaSwitchSolVfFArbitrationPriority

Bspec mentions this for HSW+. I can't quite tell what the effects are,
and I don't easily have a way to test this.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -121,6 +121,7 @@
 
 #define GAM_ECOCHK			0x4090
 #define   ECOCHK_SNB_BIT		(1<<10)
+#define   HSW_ECOCHK_ARB_PRIO_SOL	(1<<6)
 #define   ECOCHK_PPGTT_CACHE64B		(0x3<<3)
 #define   ECOCHK_PPGTT_CACHE4B		(0x0<<3)
 

drivers/gpu/drm/i915/intel_pm.c

@@ -3770,6 +3770,9 @@ static void haswell_init_clock_gating(struct drm_device *dev)
 	I915_WRITE(GEN6_MBCTL, I915_READ(GEN6_MBCTL) |
 		   GEN6_MBCTL_ENABLE_BOOT_FETCH);
 
+	/* WaSwitchSolVfFArbitrationPriority */
+	I915_WRITE(GAM_ECOCHK, I915_READ(GAM_ECOCHK) | HSW_ECOCHK_ARB_PRIO_SOL);
+
 	/* XXX: This is a workaround for early silicon revisions and should be
 	 * removed later.
 	 */