video: backlight: Parse PWM polarity cell

This patch enables the reading of the polarity cell from a PWM
phandle and calls pwm_set_invert().

Not all platforms have polarity cell, so skip if it's not pressent.
Signed-off-by: NStefan Mavrodiev <stefan@olimex.com>
Reviewed-by: NAnatolij Gustschin <agust@denx.de>

drivers/video/pwm_backlight.c

@@ -39,6 +39,12 @@ struct pwm_backlight_priv {
 	struct udevice *pwm;
 	uint channel;
 	uint period_ns;
+	/*
+	 * the polarity of one PWM
+	 * 0: normal polarity
+	 * 1: inverted polarity
+	 */
+	bool polarity;
 	u32 *levels;
 	int num_levels;
 	uint default_level;
@@ -57,7 +63,10 @@ static int set_pwm(struct pwm_backlight_priv *priv)
 		(priv->max_level - priv->min_level + 1);
 	ret = pwm_set_config(priv->pwm, priv->channel, priv->period_ns,
 			     duty_cycle);
+	if (ret)
+		return log_ret(ret);
 
+	ret = pwm_set_invert(priv->pwm, priv->channel, priv->polarity);
 	return log_ret(ret);
 }
 
@@ -202,6 +211,8 @@ static int pwm_backlight_ofdata_to_platdata(struct udevice *dev)
 		return log_msg_ret("Not enough arguments to pwm\n", -EINVAL);
 	priv->channel = args.args[0];
 	priv->period_ns = args.args[1];
+	if (args.args_count > 2)
+		priv->polarity = args.args[2];
 
 	index = dev_read_u32_default(dev, "default-brightness-level", 255);
 	cell = dev_read_prop(dev, "brightness-levels", &len);