drm/i915: panel: Use intel_panel_compute_brightness() from pwm_setup_backlight()

Use intel_panel_compute_brightness() from pwm_setup_backlight() so that
we correctly take i915_modparams.invert_brightness and/or
QUIRK_INVERT_BRIGHTNESS into account when setting + getting the initial
brightness value.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200221172927.510027-1-hdegoede@redhat.com

drivers/gpu/drm/i915/display/intel_panel.c

@@ -1882,6 +1882,7 @@ static int pwm_setup_backlight(struct intel_connector *connector,
 	struct drm_i915_private *dev_priv = to_i915(dev);
 	struct intel_panel *panel = &connector->panel;
 	const char *desc;
+	u32 level, ns;
 	int retval;
 
 	/* Get the right PWM chip for DSI backlight according to VBT */
@@ -1906,8 +1907,12 @@ static int pwm_setup_backlight(struct intel_connector *connector,
 	 */
 	pwm_apply_args(panel->backlight.pwm);
 
-	retval = pwm_config(panel->backlight.pwm, CRC_PMIC_PWM_PERIOD_NS,
-			    CRC_PMIC_PWM_PERIOD_NS);
+	panel->backlight.min = 0; /* 0% */
+	panel->backlight.max = 100; /* 100% */
+	level = intel_panel_compute_brightness(connector, 100);
+	ns = DIV_ROUND_UP(level * CRC_PMIC_PWM_PERIOD_NS, 100);
+
+	retval = pwm_config(panel->backlight.pwm, ns, CRC_PMIC_PWM_PERIOD_NS);
 	if (retval < 0) {
 		drm_err(&dev_priv->drm, "Failed to configure the pwm chip\n");
 		pwm_put(panel->backlight.pwm);
@@ -1915,11 +1920,10 @@ static int pwm_setup_backlight(struct intel_connector *connector,
 		return retval;
 	}
 
-	panel->backlight.min = 0; /* 0% */
-	panel->backlight.max = 100; /* 100% */
-	panel->backlight.level = DIV_ROUND_UP(
-				 pwm_get_duty_cycle(panel->backlight.pwm) * 100,
+	level = DIV_ROUND_UP(pwm_get_duty_cycle(panel->backlight.pwm) * 100,
 			     CRC_PMIC_PWM_PERIOD_NS);
+	panel->backlight.level =
+		intel_panel_compute_brightness(connector, level);
 	panel->backlight.enabled = panel->backlight.level != 0;
 
 	drm_info(&dev_priv->drm, "Using %s PWM for LCD backlight control\n",