drm/i915: sanitize enable_rc6 option

Atm, an invalid enable_rc6 module option will be silently ignored, so
emit an info message about it. Doing an early sanitization we can also
reuse intel_enable_rc6() in a follow-up patch to see if RC6 is actually
enabled. Currently the caller would have to filter a non-zero return
value based on the platform we are running on. For example on VLV with
i915.enable_rc6 set to 2, RC6 won't be enabled but atm
intel_enable_rc6() would still return 2 in this case.

v2:
- simplify the platform check condition (Ville)
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -3262,15 +3262,32 @@ static void intel_print_rc6_info(struct drm_device *dev, u32 mode)
 		 (mode & GEN6_RC_CTL_RC6pp_ENABLE) ? "on" : "off");
 }
 
-int intel_enable_rc6(const struct drm_device *dev)
+static int sanitize_rc6_option(const struct drm_device *dev, int enable_rc6)
 {
 	/* No RC6 before Ironlake */
 	if (INTEL_INFO(dev)->gen < 5)
 		return 0;
 
+	/* RC6 is only on Ironlake mobile not on desktop */
+	if (INTEL_INFO(dev)->gen == 5 && !IS_IRONLAKE_M(dev))
+		return 0;
+
 	/* Respect the kernel parameter if it is set */
-	if (i915.enable_rc6 >= 0)
-		return i915.enable_rc6;
+	if (enable_rc6 >= 0) {
+		int mask;
+
+		if (INTEL_INFO(dev)->gen == 6 || IS_IVYBRIDGE(dev))
+			mask = INTEL_RC6_ENABLE | INTEL_RC6p_ENABLE |
+			       INTEL_RC6pp_ENABLE;
+		else
+			mask = INTEL_RC6_ENABLE;
+
+		if ((enable_rc6 & mask) != enable_rc6)
+			DRM_INFO("Adjusting RC6 mask to %d (requested %d, valid %d)\n",
+				 enable_rc6, enable_rc6 & mask, mask);
+
+		return enable_rc6 & mask;
+	}
 
 	/* Disable RC6 on Ironlake */
 	if (INTEL_INFO(dev)->gen == 5)
@@ -3282,6 +3299,11 @@ int intel_enable_rc6(const struct drm_device *dev)
 	return INTEL_RC6_ENABLE;
 }
 
+int intel_enable_rc6(const struct drm_device *dev)
+{
+	return i915.enable_rc6;
+}
+
 static void gen6_enable_rps_interrupts(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -4496,6 +4518,8 @@ static void intel_init_emon(struct drm_device *dev)
 
 void intel_init_gt_powersave(struct drm_device *dev)
 {
+	i915.enable_rc6 = sanitize_rc6_option(dev, i915.enable_rc6);
+
 	if (IS_VALLEYVIEW(dev))
 		valleyview_setup_pctx(dev);
 }