1 files changed, 42 insertions, 10 deletions

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 92ff8f38527..7350ec2515c 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -125,15 +125,55 @@ static int is_backlight_combination_mode(struct drm_device *dev)
 	return 0;
 }
 
+static u32 i915_read_blc_pwm_ctl(struct drm_i915_private *dev_priv)
+{
+	u32 val;
+
+	/* Restore the CTL value if it lost, e.g. GPU reset */
+
+	if (HAS_PCH_SPLIT(dev_priv->dev)) {
+		val = I915_READ(BLC_PWM_PCH_CTL2);
+		if (dev_priv->saveBLC_PWM_CTL2 == 0) {
+			dev_priv->saveBLC_PWM_CTL2 = val;
+		} else if (val == 0) {
+			I915_WRITE(BLC_PWM_PCH_CTL2,
+				   dev_priv->saveBLC_PWM_CTL);
+			val = dev_priv->saveBLC_PWM_CTL;
+		}
+	} else {
+		val = I915_READ(BLC_PWM_CTL);
+		if (dev_priv->saveBLC_PWM_CTL == 0) {
+			dev_priv->saveBLC_PWM_CTL = val;
+			dev_priv->saveBLC_PWM_CTL2 = I915_READ(BLC_PWM_CTL2);
+		} else if (val == 0) {
+			I915_WRITE(BLC_PWM_CTL,
+				   dev_priv->saveBLC_PWM_CTL);
+			I915_WRITE(BLC_PWM_CTL2,
+				   dev_priv->saveBLC_PWM_CTL2);
+			val = dev_priv->saveBLC_PWM_CTL;
+		}
+	}
+
+	return val;
+}
+
 u32 intel_panel_get_max_backlight(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	u32 max;
 
+	max = i915_read_blc_pwm_ctl(dev_priv);
+	if (max == 0) {
+		/* XXX add code here to query mode clock or hardware clock
+		 * and program max PWM appropriately.
+		 */
+		printk_once(KERN_WARNING "fixme: max PWM is zero.\n");
+		return 1;
+	}
+
 	if (HAS_PCH_SPLIT(dev)) {
-		max = I915_READ(BLC_PWM_PCH_CTL2) >> 16;
+		max >>= 16;
 	} else {
-		max = I915_READ(BLC_PWM_CTL);
 		if (IS_PINEVIEW(dev)) {
 			max >>= 17;
 		} else {
@@ -146,14 +186,6 @@ u32 intel_panel_get_max_backlight(struct drm_device *dev)
 			max *= 0xff;
 	}
 
-	if (max == 0) {
-		/* XXX add code here to query mode clock or hardware clock
-		 * and program max PWM appropriately.
-		 */
-		DRM_ERROR("fixme: max PWM is zero.\n");
-		max = 1;
-	}
-
 	DRM_DEBUG_DRIVER("max backlight PWM = %d\n", max);
 	return max;
 }