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

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Message-ID: <56FAE8CD.1010804@gmail.com>
Date:	Tue, 29 Mar 2016 22:42:53 +0200
From:	Heiner Kallweit <hkallweit1@...il.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Jacek Anaszewski <j.anaszewski@...sung.com>,
	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 29.03.2016 um 12:05 schrieb Pavel Machek:
> On Tue 2016-03-01 22:36:12, 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
>> +	 */
>> +	WARN_ON(led_cdev->flags & LED_DEV_CAP_RGB && led_cdev->brightness_get);
>> +
> 
> Backtrace is useless here, you may want to add some ()s and you don't
> really want user to be causing messages in syslog this easily.
> 
I agree that the backtrace doesn't provide a benefit here.

However I don't see how a user could create syslog entries.
The warn condition can be true only for drivers implementing the RGB extension
in a not supported way (by setting flag LED_DEV_CAP_RGB and implementing
brightness_get).

									Pavel
>