drm/i915/lvds: Always restore panel-fitter when enabling the LVDS

Linus Torvalds pointed out that our code was unbalanced when powering on
the panel with respect to the power off sequence in that we were failing
to restore the panel-fitter. The consequence of this would be that
across a simple DPMS off/on for a non-native mode, without an intervening
modeset, the panel fitter would remain disabled and the output would shift
on the panel.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_lvds.c

@@ -68,7 +68,7 @@ static struct intel_lvds *intel_attached_lvds(struct drm_connector *connector)
 /**
  * Sets the power state for the panel.
  */
-static void intel_lvds_set_power(struct intel_lvds *intel_lvds, bool on)
+static void intel_lvds_enable(struct intel_lvds *intel_lvds)
 {
 	struct drm_device *dev = intel_lvds->base.base.dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -82,26 +82,61 @@ static void intel_lvds_set_power(struct intel_lvds *intel_lvds, bool on)
 		lvds_reg = LVDS;
 	}
 
-	if (on) {
-		I915_WRITE(lvds_reg, I915_READ(lvds_reg) | LVDS_PORT_EN);
-		I915_WRITE(ctl_reg, I915_READ(ctl_reg) | POWER_TARGET_ON);
-		intel_panel_set_backlight(dev, dev_priv->backlight_level);
-	} else {
-		dev_priv->backlight_level = intel_panel_get_backlight(dev);
-
-		intel_panel_set_backlight(dev, 0);
-		I915_WRITE(ctl_reg, I915_READ(ctl_reg) & ~POWER_TARGET_ON);
+	I915_WRITE(lvds_reg, I915_READ(lvds_reg) | LVDS_PORT_EN);
 
-		if (intel_lvds->pfit_control) {
-			if (wait_for((I915_READ(PP_STATUS) & PP_ON) == 0, 1000))
-				DRM_ERROR("timed out waiting for panel to power off\n");
-			I915_WRITE(PFIT_CONTROL, 0);
-			intel_lvds->pfit_control = 0;
+	if (intel_lvds->pfit_dirty) {
+		/*
+		 * Enable automatic panel scaling so that non-native modes
+		 * fill the screen.  The panel fitter should only be
+		 * adjusted whilst the pipe is disabled, according to
+		 * register description and PRM.
+		 */
+		DRM_DEBUG_KMS("applying panel-fitter: %x, %x\n",
+			      intel_lvds->pfit_control,
+			      intel_lvds->pfit_pgm_ratios);
+		if (wait_for((I915_READ(PP_STATUS) & PP_ON) == 0, 1000)) {
+			DRM_ERROR("timed out waiting for panel to power off\n");
+		} else {
+			I915_WRITE(PFIT_PGM_RATIOS, intel_lvds->pfit_pgm_ratios);
+			I915_WRITE(PFIT_CONTROL, intel_lvds->pfit_control);
 			intel_lvds->pfit_dirty = false;
 		}
+	}
+
+	I915_WRITE(ctl_reg, I915_READ(ctl_reg) | POWER_TARGET_ON);
+	POSTING_READ(lvds_reg);
+
+	intel_panel_set_backlight(dev, dev_priv->backlight_level);
+}
 
-		I915_WRITE(lvds_reg, I915_READ(lvds_reg) & ~LVDS_PORT_EN);
+static void intel_lvds_disable(struct intel_lvds *intel_lvds)
+{
+	struct drm_device *dev = intel_lvds->base.base.dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	u32 ctl_reg, lvds_reg;
+
+	if (HAS_PCH_SPLIT(dev)) {
+		ctl_reg = PCH_PP_CONTROL;
+		lvds_reg = PCH_LVDS;
+	} else {
+		ctl_reg = PP_CONTROL;
+		lvds_reg = LVDS;
+	}
+
+	dev_priv->backlight_level = intel_panel_get_backlight(dev);
+	intel_panel_set_backlight(dev, 0);
+
+	I915_WRITE(ctl_reg, I915_READ(ctl_reg) & ~POWER_TARGET_ON);
+
+	if (intel_lvds->pfit_control) {
+		if (wait_for((I915_READ(PP_STATUS) & PP_ON) == 0, 1000))
+			DRM_ERROR("timed out waiting for panel to power off\n");
+
+		I915_WRITE(PFIT_CONTROL, 0);
+		intel_lvds->pfit_dirty = true;
 	}
+
+	I915_WRITE(lvds_reg, I915_READ(lvds_reg) & ~LVDS_PORT_EN);
 	POSTING_READ(lvds_reg);
 }
 
@@ -110,9 +145,9 @@ static void intel_lvds_dpms(struct drm_encoder *encoder, int mode)
 	struct intel_lvds *intel_lvds = to_intel_lvds(encoder);
 
 	if (mode == DRM_MODE_DPMS_ON)
-		intel_lvds_set_power(intel_lvds, true);
+		intel_lvds_enable(intel_lvds);
 	else
-		intel_lvds_set_power(intel_lvds, false);
+		intel_lvds_disable(intel_lvds);
 
 	/* XXX: We never power down the LVDS pairs. */
 }
@@ -411,43 +446,18 @@ static void intel_lvds_commit(struct drm_encoder *encoder)
 	/* Always do a full power on as we do not know what state
 	 * we were left in.
 	 */
-	intel_lvds_set_power(intel_lvds, true);
+	intel_lvds_enable(intel_lvds);
 }
 
 static void intel_lvds_mode_set(struct drm_encoder *encoder,
 				struct drm_display_mode *mode,
 				struct drm_display_mode *adjusted_mode)
 {
-	struct drm_device *dev = encoder->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	struct intel_lvds *intel_lvds = to_intel_lvds(encoder);
-
 	/*
 	 * The LVDS pin pair will already have been turned on in the
 	 * intel_crtc_mode_set since it has a large impact on the DPLL
 	 * settings.
 	 */
-
-	if (HAS_PCH_SPLIT(dev))
-		return;
-
-	if (!intel_lvds->pfit_dirty)
-		return;
-
-	/*
-	 * Enable automatic panel scaling so that non-native modes fill the
-	 * screen.  Should be enabled before the pipe is enabled, according to
-	 * register description and PRM.
-	 */
-	DRM_DEBUG_KMS("applying panel-fitter: %x, %x\n",
-		      intel_lvds->pfit_control,
-		      intel_lvds->pfit_pgm_ratios);
-	if (wait_for((I915_READ(PP_STATUS) & PP_ON) == 0, 1000))
-		DRM_ERROR("timed out waiting for panel to power off\n");
-
-	I915_WRITE(PFIT_PGM_RATIOS, intel_lvds->pfit_pgm_ratios);
-	I915_WRITE(PFIT_CONTROL, intel_lvds->pfit_control);
-	intel_lvds->pfit_dirty = false;
 }
 
 /**