linux-kernel - Re: [PATCH v4 2/2] documention: leds: Add multicolor class documentation

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Message-ID: <d5bdf93b-2a6e-a773-ebb1-4850859ed147@gmail.com>
Date:   Sun, 9 Jun 2019 17:15:57 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Dan Murphy <dmurphy@...com>, pavel@....cz
Cc:     linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] documention: leds: Add multicolor class
 documentation

Hi Dan,

On 5/30/19 8:16 PM, Dan Murphy wrote:
[...]
> +Multicolor Class Brightness Control
> +-----------------------------------
> +The multicolor class will redirect the device drivers call back
> +function for brightness control to the multicolor class brightness
> +control function.
> +
> +The brightness level for each LED is calculated based on the color LED
> +brightness setting divided by the color LED max brightness setting multiplied by
> +the requested value.
> +
> +led_brightness = requested_value*(led_color_brightness/led_color_max_brightness)
> +
> +Example:
> +Three LEDs are present in the group as defined in "Directory Layout Example"
> +within this document.
> +
> +A user first writes the color LED brightness file with the brightness level that
> +is neccesary to achieve a blueish violet output from the RGB LED group.
> +
> +echo 138 > /sys/class/leds/rgb:grouped_leds/red/brightness
> +echo 43 > /sys/class/leds/rgb:grouped_leds/green/brightness
> +echo 226 > /sys/class/leds/rgb:grouped_leds/blue/brightness
> +
> +red -
> +	brightness = 138
> +	max_brightness = 255
> +green -
> +	brightness = 43
> +	max_brightness = 255
> +blue -
> +	brightness = 226
> +	max_brightness = 255
> +
> +The user can control the brightness of that RGB group by writing the parent
> +'brightness' control.  Assuming a parent max_brightness of 255 the user may want
> +to dim the LED color group to half.  The user would write a value of 128 to the
> +parent brightness file then the values written to each LED will be adjusted
> +base on this value
> +
> +cat /sys/class/leds/rgb:grouped_leds/max_brightness
> +255
> +echo 128 > /sys/class/leds/rgb:grouped_leds/brightness
> +
> +adjusted_red_value = 128 * (138/255) = 69
> +adjusted_green_value = 128 * (43/255) = 21
> +adjusted_blue_value = 128 * (226/255) = 113
> +
> +Reading the parent brightness file will return the current brightness value of
> +the color LED group.

I've tested this algorithm with python script and at least on my LED 
monitor it works as expected. Attached is the script I've come up with.

> +cat /sys/class/leds/rgb:grouped_leds/max_brightness
> +255
> +
> +echo 128 > /sys/class/leds/rgb:grouped_leds/brightness
> +
> +cat /sys/class/leds/rgb:grouped_leds/max_brightness
> +128
> +
> +
> 

-- 
Best regards,
Jacek Anaszewski

View attachment "led_color.py" of type "text/x-python" (828 bytes)