drm/i915/backlight: handle enabled but zero duty cycle at module load

Don't consider enabled but zero duty cycle backlight disabled. Clamp
level between min and max for sanity.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471939811-9817-1-git-send-email-maarten.lankhorst@linux.intel.com
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/i915/intel_panel.c

@@ -1430,10 +1430,11 @@ static int lpt_setup_backlight(struct intel_connector *connector, enum pipe unus
 	panel->backlight.min = get_backlight_min_vbt(connector);
 
 	val = lpt_get_backlight(connector);
-	panel->backlight.level = intel_panel_compute_brightness(connector, val);
+	val = intel_panel_compute_brightness(connector, val);
+	panel->backlight.level = clamp(val, panel->backlight.min,
+				       panel->backlight.max);
 
-	panel->backlight.enabled = (pch_ctl1 & BLM_PCH_PWM_ENABLE) &&
-		panel->backlight.level != 0;
+	panel->backlight.enabled = pch_ctl1 & BLM_PCH_PWM_ENABLE;
 
 	return 0;
 }
@@ -1459,11 +1460,13 @@ static int pch_setup_backlight(struct intel_connector *connector, enum pipe unus
 	panel->backlight.min = get_backlight_min_vbt(connector);
 
 	val = pch_get_backlight(connector);
-	panel->backlight.level = intel_panel_compute_brightness(connector, val);
+	val = intel_panel_compute_brightness(connector, val);
+	panel->backlight.level = clamp(val, panel->backlight.min,
+				       panel->backlight.max);
 
 	cpu_ctl2 = I915_READ(BLC_PWM_CPU_CTL2);
 	panel->backlight.enabled = (cpu_ctl2 & BLM_PWM_ENABLE) &&
-		(pch_ctl1 & BLM_PCH_PWM_ENABLE) && panel->backlight.level != 0;
+		(pch_ctl1 & BLM_PCH_PWM_ENABLE);
 
 	return 0;
 }
@@ -1498,9 +1501,11 @@ static int i9xx_setup_backlight(struct intel_connector *connector, enum pipe unu
 	panel->backlight.min = get_backlight_min_vbt(connector);
 
 	val = i9xx_get_backlight(connector);
-	panel->backlight.level = intel_panel_compute_brightness(connector, val);
+	val = intel_panel_compute_brightness(connector, val);
+	panel->backlight.level = clamp(val, panel->backlight.min,
+				       panel->backlight.max);
 
-	panel->backlight.enabled = panel->backlight.level != 0;
+	panel->backlight.enabled = val != 0;
 
 	return 0;
 }
@@ -1530,10 +1535,11 @@ static int i965_setup_backlight(struct intel_connector *connector, enum pipe unu
 	panel->backlight.min = get_backlight_min_vbt(connector);
 
 	val = i9xx_get_backlight(connector);
-	panel->backlight.level = intel_panel_compute_brightness(connector, val);
+	val = intel_panel_compute_brightness(connector, val);
+	panel->backlight.level = clamp(val, panel->backlight.min,
+				       panel->backlight.max);
 
-	panel->backlight.enabled = (ctl2 & BLM_PWM_ENABLE) &&
-		panel->backlight.level != 0;
+	panel->backlight.enabled = ctl2 & BLM_PWM_ENABLE;
 
 	return 0;
 }
@@ -1562,10 +1568,11 @@ static int vlv_setup_backlight(struct intel_connector *connector, enum pipe pipe
 	panel->backlight.min = get_backlight_min_vbt(connector);
 
 	val = _vlv_get_backlight(dev_priv, pipe);
-	panel->backlight.level = intel_panel_compute_brightness(connector, val);
+	val = intel_panel_compute_brightness(connector, val);
+	panel->backlight.level = clamp(val, panel->backlight.min,
+				       panel->backlight.max);
 
-	panel->backlight.enabled = (ctl2 & BLM_PWM_ENABLE) &&
-		panel->backlight.level != 0;
+	panel->backlight.enabled = ctl2 & BLM_PWM_ENABLE;
 
 	return 0;
 }
@@ -1607,10 +1614,11 @@ bxt_setup_backlight(struct intel_connector *connector, enum pipe unused)
 		return -ENODEV;
 
 	val = bxt_get_backlight(connector);
-	panel->backlight.level = intel_panel_compute_brightness(connector, val);
+	val = intel_panel_compute_brightness(connector, val);
+	panel->backlight.level = clamp(val, panel->backlight.min,
+				       panel->backlight.max);
 
-	panel->backlight.enabled = (pwm_ctl & BXT_BLC_PWM_ENABLE) &&
-		panel->backlight.level != 0;
+	panel->backlight.enabled = pwm_ctl & BXT_BLC_PWM_ENABLE;
 
 	return 0;
 }