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

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Message-ID: <d453c7e3-022e-4f5b-bdf1-a78ed5cef4f4@prodrive-technologies.com>
Date: Wed, 19 Nov 2025 19:24:13 +0100
From: Martijn de Gouw <martijn.de.gouw@...drive-technologies.com>
To: Lee Jones <lee@...nel.org>
Cc: Pavel Machek <pavel@...nel.org>, linux-leds@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] leds: group-multicolor: Add support for initial value.

Hi,

On 11/19/2025 5:51 PM, Lee Jones wrote:
> On Tue, 11 Nov 2025, Martijn de Gouw wrote:
> 
>> It's possible to set a default state for leds in the dts with
>> 'default-state', but this was not reflected when the LEDs are grouped.
>> This patch adds support for keeping the default-state value.
>>
>> Signed-off-by: Martijn de Gouw <martijn.de.gouw@...drive-technologies.com>
>> ---
>>  drivers/leds/rgb/leds-group-multicolor.c | 13 +++++++++++--
>>  1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/leds/rgb/leds-group-multicolor.c b/drivers/leds/rgb/leds-group-multicolor.c
>> index 548c7dd63ba1e..b3e46a51dfbc7 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;
>> +	unsigned int default_brightness = 0;
>>  	int i, ret, count = 0, common_flags = 0;
>>  
>>  	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
>> @@ -96,6 +97,12 @@ 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.
>> +		 */
> 
> I don't know this code well, but if no one complains, I can take your
> word for this.
> 
> However, the comment needs changing to proper multi-line format.
> 
>         /*
>          * This is the preferred style for multi-line
>          * comments in the Linux kernel source code.
>          * Please use it consistently.
>          *
>          * Description:  A column of asterisks on the left side,
>          * with beginning and ending almost-blank lines.
>          */

Will do!

> 
>> +		if (led_cdev->brightness)
>> +			default_brightness = max_brightness;
>> +
>>  		count++;
>>  	}
>>  
>> @@ -109,14 +116,16 @@ 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,
> 
> How does this work?  Won't this value be huge?

It calculates the intensity of the led with respect to the max_brightness of the whole group.
So actually it's doing:
subled[i].intensity = group->max_brightness * (led_cdev->brightness/led_cdev->max_brightness).

I highest value I could find for a max_brightness is 4096 (12 bit). Maybe some PWM LEDs use up to 16bit?
So I made the assumption that is should not be an issue.
I wrote it this way, where the multiplication comes first, because integer divisions don't work well.
> 
>> +							led_cdev->max_brightness);
> 
> Also we said we were going to set actual brightness with the intensity
> in the comment above, but we appear to be using max_brightness again?

I'll try to clarify the comments.

> 
>>  	}
>>  
>>  	/* 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 = default_brightness;
>>  	cdev->color = LED_COLOR_ID_MULTI;
>>  	priv->mc_cdev.num_colors = count;
>>  
>> -- 
>> 2.39.2
>>
> 

-- 
Martijn de Gouw
Designer
Prodrive Technologies B.V.
Mobile: +31 63 17 76 161
Phone:  +31 40 26 76 200