drm/i915/bdw: Use timeout mode for RC6 on bdw

Higher RC6 residency is observed using timeout mode
instead of EI mode.  This applies to Broadwell only.
The difference is particularly noticeable with video
playback.
Signed-off-by: Tom O'Rourke <Tom.O'Rourke@intel.com>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_pm.c

@@ -3486,12 +3486,20 @@ static void gen8_enable_rps(struct drm_device *dev)
 	for_each_ring(ring, dev_priv, unused)
 		I915_WRITE(RING_MAX_IDLE(ring->mmio_base), 10);
 	I915_WRITE(GEN6_RC_SLEEP, 0);
+	if (IS_BROADWELL(dev))
+		I915_WRITE(GEN6_RC6_THRESHOLD, 625); /* 800us/1.28 for TO */
+	else
 		I915_WRITE(GEN6_RC6_THRESHOLD, 50000); /* 50/125ms per EI */
 
 	/* 3: Enable RC6 */
 	if (intel_enable_rc6(dev) & INTEL_RC6_ENABLE)
 		rc6_mask = GEN6_RC_CTL_RC6_ENABLE;
 	intel_print_rc6_info(dev, rc6_mask);
+	if (IS_BROADWELL(dev))
+		I915_WRITE(GEN6_RC_CONTROL, GEN6_RC_CTL_HW_ENABLE |
+				GEN7_RC_CTL_TO_MODE |
+				rc6_mask);
+	else
 		I915_WRITE(GEN6_RC_CONTROL, GEN6_RC_CTL_HW_ENABLE |
 				GEN6_RC_CTL_EI_MODE(1) |
 				rc6_mask);