[PATCH] leds: pwm: Fix active-low brightness with default-state keep

[PATCH] leds: pwm: Fix active-low brightness with default-state keep

[raoxu]

From: Xu Rao <raoxu@uniontech.com>

With default-state set to "keep", led_pwm_add() derives the initial
brightness from the PWM duty cycle without accounting for active-low
LEDs. However, led_pwm_set() inverts the duty cycle for these LEDs.

For an enabled active-low PWM with zero duty cycle, the LED is fully
on but its cached brightness is set to zero. Conversely, a full duty
cycle is reported as maximum brightness instead of off. This exposes
an incorrect brightness to userspace and can restore the wrong value
after suspend. With an optional enable GPIO, the incorrect brightness
also causes the wrong initial GPIO level to be selected.

Invert the computed brightness for active-low LEDs, matching the
conversion used by led_pwm_set() while leaving the PWM state intact.

The supplied fix was reviewed and this commit message prepared with
OpenCode AI assistance.

Fixes: 3d3d65bd2764 ("leds: pwm: add support for default-state device property")
Signed-off-by: Xu Rao <raoxu@uniontech.com>
Cc: stable@vger.kernel.org
---
 drivers/leds/leds-pwm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/leds/leds-pwm.c b/drivers/leds/leds-pwm.c
index 6c1f2f50ff85..da307767dbe8 100644
--- a/drivers/leds/leds-pwm.c
+++ b/drivers/leds/leds-pwm.c
@@ -131,6 +131,8 @@ static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv,
 		brightness = led->max_brightness;
 		brightness *= led_data->pwmstate.duty_cycle;
 		do_div(brightness, led_data->pwmstate.period);
+		if (led_data->active_low)
+			brightness = led->max_brightness - brightness;
 		led_data->cdev.brightness = brightness;
 		}
 		break;
--
2.50.1

Re: [PATCH] leds: pwm: Fix active-low brightness with default-state keep

[sashiko-bot]

> From: Xu Rao <raoxu@uniontech.com>
> 
> With default-state set to "keep", led_pwm_add() derives the initial
> brightness from the PWM duty cycle without accounting for active-low
> LEDs. However, led_pwm_set() inverts the duty cycle for these LEDs.
> 
> For an enabled active-low PWM with zero duty cycle, the LED is fully
> on but its cached brightness is set to zero. Conversely, a full duty
> cycle is reported as maximum brightness instead of off. This exposes
> an incorrect brightness to userspace and can restore the wrong value
> after suspend. With an optional enable GPIO, the incorrect brightness
> also causes the wrong initial GPIO level to be selected.
> 
> Invert the computed brightness for active-low LEDs, matching the
> conversion used by led_pwm_set() while leaving the PWM state intact.
> 
> The supplied fix was reviewed and this commit message prepared with
> OpenCode AI assistance.
> 
> Fixes: 3d3d65bd2764 ("leds: pwm: add support for default-state device property")
> Signed-off-by: Xu Rao <raoxu@uniontech.com>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/9524E319B9AF9D1A+20261109085822.3755803-1-raoxu@uniontech.com?part=1