[PATCH 1/2] video: backlight: Support PWMs without a known period_ns

[Alper Nebi Yasak <alpernebiyasak@gmail.com>]

The PWM device provided by Chrome OS EC doesn't really support anything
other than setting a relative duty cycle. To support it as a backlight,
this patch makes the PWM period optional in the device tree and pretends
the valid brightness range is its period_ns.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
---

 drivers/video/pwm_backlight.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/video/pwm_backlight.c b/drivers/video/pwm_backlight.c
index 468a5703bd..4c2a307462 100644
--- a/drivers/video/pwm_backlight.c
+++ b/drivers/video/pwm_backlight.c
@@ -62,10 +62,17 @@ static int set_pwm(struct pwm_backlight_priv *priv)
 	uint duty_cycle;
 	int ret;
 
-	duty_cycle = priv->period_ns * (priv->cur_level - priv->min_level) /
-		(priv->max_level - priv->min_level + 1);
-	ret = pwm_set_config(priv->pwm, priv->channel, priv->period_ns,
-			     duty_cycle);
+	if (priv->period_ns) {
+		duty_cycle = priv->period_ns * (priv->cur_level - priv->min_level) /
+			(priv->max_level - priv->min_level + 1);
+		ret = pwm_set_config(priv->pwm, priv->channel, priv->period_ns,
+				     duty_cycle);
+	} else {
+		/* PWM driver will internally scale these like the above. */
+		ret = pwm_set_config(priv->pwm, priv->channel,
+				     priv->max_level - priv->min_level + 1,
+				     priv->cur_level - priv->min_level);
+	}
 	if (ret)
 		return log_ret(ret);
 
@@ -213,10 +220,11 @@ static int pwm_backlight_ofdata_to_platdata(struct udevice *dev)
 		log_debug("Cannot get PWM: ret=%d\n", ret);
 		return log_ret(ret);
 	}
-	if (args.args_count < 2)
+	if (args.args_count < 1)
 		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 > 1)
+		priv->period_ns = args.args[1];
 	if (args.args_count > 2)
 		priv->polarity = args.args[2];
 
-- 
2.28.0