Re: [PATCH] leds: group-multicolor: Add support for initial value.

[Lee Jones <lee@kernel.org>]

On Mon, 16 Mar 2026, Martijn de Gouw wrote:

> When the driver is loaded, it turned off all LEDs in the group. This
> patch changes the driver to take over existing LED states and set
> the brighness and intensity in the group accordingly.
> 
> Signed-off-by: Martijn de Gouw <martijn.de.gouw@prodrive-technologies.com>
> ---
> Changes in v3:
> - Use is_on boolean instead of storing the max_brightness twice
> - Link to v2: https://lore.kernel.org/linux-leds/20251124210521.2064660-1-martijn.de.gouw@prodrive-technologies.com/
> 
> Changes in v2:
> - Fix multiline comments
> - Improve comments
> - Link to v1: https://lore.kernel.org/linux-leds/20251111204556.2803878-1-martijn.de.gouw@prodrive-technologies.com/
> 
> ---
>  drivers/leds/rgb/leds-group-multicolor.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/leds/rgb/leds-group-multicolor.c b/drivers/leds/rgb/leds-group-multicolor.c
> index 548c7dd63ba1e..ab46537697d76 100644
> --- a/drivers/leds/rgb/leds-group-multicolor.c
> +++ b/drivers/leds/rgb/leds-group-multicolor.c
> @@ -69,6 +69,7 @@ static int leds_gmc_probe(struct platform_device *pdev)
>  	struct mc_subled *subled;
>  	struct leds_multicolor *priv;
>  	unsigned int max_brightness = 0;
> +	bool is_on = false;
>  	int i, ret, count = 0, common_flags = 0;
>  
>  	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> @@ -96,6 +97,13 @@ static int leds_gmc_probe(struct platform_device *pdev)
>  
>  		max_brightness = max(max_brightness, led_cdev->max_brightness);
>  
> +		/*
> +		 * If any LED is on, set brightness to the max brightness.
> +		 * The actual brightness of the LED is set as intensity value.
> +		 */
> +		if (led_cdev->brightness)
> +			is_on = true;
> +
>  		count++;
>  	}
>  
> @@ -109,14 +117,16 @@ static int leds_gmc_probe(struct platform_device *pdev)
>  
>  		subled[i].color_index = led_cdev->color;
>  
> -		/* Configure the LED intensity to its maximum */
> -		subled[i].intensity = max_brightness;
> +		/* Configure the LED intensity to its current brightness */
> +		subled[i].intensity = DIV_ROUND_CLOSEST(led_cdev->brightness * max_brightness,
> +							led_cdev->max_brightness);

There are a couple of potential issues on this line.

'led_cdev->max_brightness' could theoretically be zero, which would
cause a division-by-zero fault.  While the core tries to prevent this, a
defensive check might be worth while.

The multiplication 'led_cdev->brightness * max_brightness' could overflow
if both values are large.  It would be safer to cast the multiplication
to u64, like: (u64)led_cdev->brightness

Finally, and this applies to the read in the first loop as well, the
brightness field of a led_classdev is protected by 'led_sem'. To avoid a
race condition with userspace (e.g., writing to the brightness via
sysfs), we should acquire this lock before reading 'led_cdev->brightness'.

>  	}
>  
>  	/* Initialise the multicolor's LED class device */
>  	cdev = &priv->mc_cdev.led_cdev;
>  	cdev->brightness_set_blocking = leds_gmc_set;
>  	cdev->max_brightness = max_brightness;
> +	cdev->brightness = is_on ? max_brightness : 0;
>  	cdev->color = LED_COLOR_ID_MULTI;
>  	priv->mc_cdev.num_colors = count;
>  
> -- 
> 2.39.2
> 
> 

-- 
Lee Jones [李琼斯]