linux-kernel - Re: [PATCH v5 4/4] leds: core: add support for RGB LED's

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Message-id: <56D94FCC.8050706@samsung.com>
Date:	Fri, 04 Mar 2016 10:05:16 +0100
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Heiner Kallweit <hkallweit1@...il.com>
Cc:	linux-leds@...r.kernel.org,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/4] leds: core: add support for RGB LED's

On 03/01/2016 10:36 PM, Heiner Kallweit wrote:
> Export a function to convert HSV color values to RGB.
> It's intended to be called by drivers for RGB LEDs.
>
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> ---
> v2:
> - move hsv -> rgb conversion to separate file
> - remove flag LED_DEV_CAP_RGB
> v3:
> - call led_hsv_to_rgb only if LED_DEV_CAP_HSV is set
>    This is needed in cases when we have monochrome and color LEDs
>    as well in a system.
> v4:
> - Export led_hsv_to_rgb and let the device driver call it instead
>    of doing the conversion in the core
> v5:
> - don't ignore led_cdev->brightness_get silently if LED_DEV_CAP_RGB
>    is set but warn
> ---
>   drivers/leds/led-class.c    |  7 +++++++
>   drivers/leds/led-rgb-core.c | 36 ++++++++++++++++++++++++++++++++++++
>   include/linux/leds.h        |  8 ++++++++
>   3 files changed, 51 insertions(+)
>
> diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
> index 8a3748a..a4b144e 100644
> --- a/drivers/leds/led-class.c
> +++ b/drivers/leds/led-class.c
> @@ -193,6 +193,13 @@ int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
>   	char name[64];
>   	int ret;
>
> +	/*
> +	 * 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
> +	 */

Does the "for now" mean that you plan on supporting it in the future?

> +	WARN_ON(led_cdev->flags & LED_DEV_CAP_RGB && led_cdev->brightness_get);
> +

Could you move this warning to the line 216?

>   	ret = led_classdev_next_name(led_cdev->name, name, sizeof(name));
>   	if (ret < 0)
>   		return ret;
> diff --git a/drivers/leds/led-rgb-core.c b/drivers/leds/led-rgb-core.c
> index f6591f1..2b18d4c 100644
> --- a/drivers/leds/led-rgb-core.c
> +++ b/drivers/leds/led-rgb-core.c
> @@ -38,3 +38,39 @@ enum led_brightness led_confine_brightness(struct led_classdev *led_cdev,
>   	return brightness |
>   	       min(value & LED_BRIGHTNESS_MASK, led_cdev->max_brightness);
>   }
> +
> +enum led_brightness led_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;
> +}
> +EXPORT_SYMBOL_GPL(led_hsv_to_rgb);
> diff --git a/include/linux/leds.h b/include/linux/leds.h
> index bbf24bb..82b3477 100644
> --- a/include/linux/leds.h
> +++ b/include/linux/leds.h
> @@ -226,6 +226,14 @@ static inline bool led_sysfs_is_disabled(struct led_classdev *led_cdev)
>   	return led_cdev->flags & LED_SYSFS_DISABLE;
>   }
>
> +/**
> + * led_hsv_to_rgb - convert a hsv color value to rgb color model
> + * @hsv: the hsv value to convert
> + *
> + * Returns: the resulting rgb value
> + */
> +enum led_brightness led_hsv_to_rgb(enum led_brightness hsv);
> +
>   /*
>    * LED Triggers
>    */
>


-- 
Best regards,
Jacek Anaszewski