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

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Date:	Fri, 4 Mar 2016 22:21:33 +0100
From:	Heiner Kallweit <hkallweit1@...il.com>
To:	Jacek Anaszewski <j.anaszewski@...sung.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

Am 04.03.2016 um 10:05 schrieb Jacek Anaszewski:
> 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?
> 
It was meant as "until somebody has an idea how to implement the conversion
HSV -> RGB -> HSV in a way that always results in the original values".
I'll remove the "for now".

>> +    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
>>    */
>>
> 
>