drm/i915: Clear pfit registers when not used by any outputs

... otherwise the panel-fitter may be left enabled with random settings
and cause unintended filtering (i.e. blurring of native modes on external
panels).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=31942Reported-and-tested-by: Ben Kohler <bkohler@gmail.com>
Tested-by: Ciprian Docan <docan@eden.rutgers.edu>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_display.c

@@ -5336,9 +5336,14 @@ static void intel_setup_outputs(struct drm_device *dev)
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_encoder *encoder;
 	bool dpd_is_edp = false;
+	bool has_lvds = false;
 
 	if (IS_MOBILE(dev) && !IS_I830(dev))
-		intel_lvds_init(dev);
+		has_lvds = intel_lvds_init(dev);
+	if (!has_lvds && !HAS_PCH_SPLIT(dev)) {
+		/* disable the panel fitter on everything but LVDS */
+		I915_WRITE(PFIT_CONTROL, 0);
+	}
 
 	if (HAS_PCH_SPLIT(dev)) {
 		dpd_is_edp = intel_dpd_is_edp(dev);

drivers/gpu/drm/i915/intel_drv.h

@@ -237,7 +237,7 @@ extern bool intel_sdvo_init(struct drm_device *dev, int output_device);
 extern void intel_dvo_init(struct drm_device *dev);
 extern void intel_tv_init(struct drm_device *dev);
 extern void intel_mark_busy(struct drm_device *dev, struct drm_gem_object *obj);
-extern void intel_lvds_init(struct drm_device *dev);
+extern bool intel_lvds_init(struct drm_device *dev);
 extern void intel_dp_init(struct drm_device *dev, int dp_reg);
 void
 intel_dp_set_m_n(struct drm_crtc *crtc, struct drm_display_mode *mode,

drivers/gpu/drm/i915/intel_lvds.c

@@ -837,7 +837,7 @@ static bool intel_lvds_ddc_probe(struct drm_device *dev, u8 pin)
  * Create the connector, register the LVDS DDC bus, and try to figure out what
  * modes we can display on the LVDS panel (if present).
  */
-void intel_lvds_init(struct drm_device *dev)
+bool intel_lvds_init(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_lvds *intel_lvds;
@@ -853,37 +853,37 @@ void intel_lvds_init(struct drm_device *dev)
 
 	/* Skip init on machines we know falsely report LVDS */
 	if (dmi_check_system(intel_no_lvds))
-		return;
+		return false;
 
 	pin = GMBUS_PORT_PANEL;
 	if (!lvds_is_present_in_vbt(dev, &pin)) {
 		DRM_DEBUG_KMS("LVDS is not present in VBT\n");
-		return;
+		return false;
 	}
 
 	if (HAS_PCH_SPLIT(dev)) {
 		if ((I915_READ(PCH_LVDS) & LVDS_DETECTED) == 0)
-			return;
+			return false;
 		if (dev_priv->edp.support) {
 			DRM_DEBUG_KMS("disable LVDS for eDP support\n");
-			return;
+			return false;
 		}
 	}
 
 	if (!intel_lvds_ddc_probe(dev, pin)) {
 		DRM_DEBUG_KMS("LVDS did not respond to DDC probe\n");
-		return;
+		return false;
 	}
 
 	intel_lvds = kzalloc(sizeof(struct intel_lvds), GFP_KERNEL);
 	if (!intel_lvds) {
-		return;
+		return false;
 	}
 
 	intel_connector = kzalloc(sizeof(struct intel_connector), GFP_KERNEL);
 	if (!intel_connector) {
 		kfree(intel_lvds);
-		return;
+		return false;
 	}
 
 	if (!HAS_PCH_SPLIT(dev)) {
@@ -1026,7 +1026,7 @@ void intel_lvds_init(struct drm_device *dev)
 	/* keep the LVDS connector */
 	dev_priv->int_lvds_connector = connector;
 	drm_sysfs_connector_add(connector);
-	return;
+	return true;
 
 failed:
 	DRM_DEBUG_KMS("No LVDS modes found, disabling.\n");
@@ -1034,4 +1034,5 @@ void intel_lvds_init(struct drm_device *dev)
 	drm_encoder_cleanup(encoder);
 	kfree(intel_lvds);
 	kfree(intel_connector);
+	return false;
 }