drm/i915/vlv: honor i915_enable_rc6 boot param on VLV

Disabling it isn't really an option on these platforms, but having it
available for power comparisons is useful.
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -3788,7 +3788,7 @@ static void valleyview_enable_rps(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_ring_buffer *ring;
-	u32 gtfifodbg, val;
+	u32 gtfifodbg, val, rc6_mode = 0;
 	int i;
 
 	WARN_ON(!mutex_is_locked(&dev_priv->rps.hw_lock));
@@ -3828,8 +3828,9 @@ static void valleyview_enable_rps(struct drm_device *dev)
 
 	/* allows RC6 residency counter to work */
 	I915_WRITE(0x138104, _MASKED_BIT_ENABLE(0x3));
-	I915_WRITE(GEN6_RC_CONTROL,
-		   GEN7_RC_CTL_TO_MODE);
+	if (intel_enable_rc6(dev) & INTEL_RC6_ENABLE)
+		rc6_mode = GEN7_RC_CTL_TO_MODE;
+	I915_WRITE(GEN6_RC_CONTROL, rc6_mode);
 
 	val = vlv_punit_read(dev_priv, PUNIT_REG_GPU_FREQ_STS);
 	switch ((val >> 6) & 3) {