Re: [PATCH 2/2] leds: core: add support for RGB LED's

[Jacek Anaszewski <j.anaszewski@samsung.com>]

On 02/07/2016 11:45 AM, Heiner Kallweit wrote:
> Add support for RGB LED's. Flag LED_DEV_CAP_RGB is used to instruct
> the core to convert HSV to RGB on output.
>
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> ---
>   drivers/leds/led-class.c |  3 +++
>   drivers/leds/led-core.c  | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
>   include/linux/leds.h     |  1 +
>   3 files changed, 51 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
> index 18a4558..f04efd2 100644
> --- a/drivers/leds/led-class.c
> +++ b/drivers/leds/led-class.c
> @@ -193,6 +193,9 @@ int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
>   	char name[64];
>   	int ret;
>
> +	if (led_cdev->flags & LED_DEV_CAP_RGB)
> +		led_cdev->flags |= LED_DEV_CAP_COLOR;
> +
>   	ret = led_classdev_next_name(led_cdev->name, name, sizeof(name));
>   	if (ret < 0)
>   		return ret;
> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
> index 798e31e..6e1adc5 100644
> --- a/drivers/leds/led-core.c
> +++ b/drivers/leds/led-core.c
> @@ -45,12 +45,50 @@ static inline enum led_brightness to_hsv(struct led_classdev *cdev,
>   	return ret | min(value & LED_BRIGHTNESS_MASK, cdev->max_brightness);
>   }
>
> +static enum led_brightness hsv_to_rgb(enum led_brightness hsv)
> +{
> +	int h = min_t(int, (hsv >> 16) & 0xff, 251);
> +	int s = (hsv >> 8) & 0xff;
> +	int v = hsv & 0xff;
> +	int f, p, q, t, r, g, b;
> +
> +	if (!v)
> +		return 0;
> +	if (!s)
> +		return (v << 16) + (v << 8) + v;
> +
> +	f = DIV_ROUND_CLOSEST((h % 42) * 255, 42);
> +	p = v - DIV_ROUND_CLOSEST(s * v, 255);
> +	q = v - DIV_ROUND_CLOSEST(f * s * v, 255 * 255);
> +	t = v - DIV_ROUND_CLOSEST((255 - f) * s * v, 255 * 255);
> +
> +	switch (h / 42) {
> +	case 0:
> +		r = v; g = t; b = p; break;
> +	case 1:
> +		r = q; g = v; b = p; break;
> +	case 2:
> +		r = p; g = v; b = t; break;
> +	case 3:
> +		r = p; g = q; b = v; break;
> +	case 4:
> +		r = t; g = p; b = v; break;
> +	case 5:
> +		r = v; g = p; b = q; break;
> +	}
> +
> +	return (r << 16) + (g << 8) + b;
> +}
> +

This can be moved to led-hvs-core.c. Could you also share a reference
to the algorithm of hsv -> rgb conversion you implemented here?

>   static int led_set_output(struct led_classdev *cdev,
>   			  enum led_brightness value)
>   {
>   	if (!cdev->brightness_set)
>   		return -ENOTSUPP;
>
> +	if (cdev->flags & LED_DEV_CAP_RGB)
> +		value = hsv_to_rgb(value);
> +
>   	cdev->brightness_set(cdev, value);
>
>   	return 0;
> @@ -62,6 +100,9 @@ static int led_set_output_blocking(struct led_classdev *cdev,
>   	if (!cdev->brightness_set_blocking)
>   		return -ENOTSUPP;
>
> +	if (cdev->flags & LED_DEV_CAP_RGB)
> +		value = hsv_to_rgb(value);
> +
>   	return cdev->brightness_set_blocking(cdev, value);
>   }
>
> @@ -320,7 +361,12 @@ int led_update_brightness(struct led_classdev *led_cdev)
>   {
>   	int ret = 0;
>
> -	if (led_cdev->brightness_get) {
> +	/*
> +	 * for now reading back the color is not supported as multiple
> +	 * HSV -> RGB -> HSV conversions may distort the color due to
> +	 * rounding issues in the conversion algorithm
> +	 */
> +	if (led_cdev->brightness_get && !(led_cdev->flags & LED_DEV_CAP_RGB)) {
>   		ret = led_cdev->brightness_get(led_cdev);
>   		if (ret >= 0) {
>   			led_cdev->brightness = ret;
> diff --git a/include/linux/leds.h b/include/linux/leds.h
> index 8e7db72..24eae4b 100644
> --- a/include/linux/leds.h
> +++ b/include/linux/leds.h
> @@ -51,6 +51,7 @@ struct led_classdev {
>   #define LED_DEV_CAP_FLASH	(1 << 23)
>   #define LED_HW_PLUGGABLE	(1 << 24)
>   #define LED_DEV_CAP_COLOR	(1 << 25)
> +#define LED_DEV_CAP_RGB		(1 << 26)

Why two flags - COLOR and RGB? Their meaning is ambiguous.

>
>   	/* Set LED brightness level
>   	 * Must not sleep. Use brightness_set_blocking for drivers
>


-- 
Best Regards,
Jacek Anaszewski