linux-kernel - Re: [PATCH v9 01/15] leds: multicolor: Add sysfs interface definition

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Date:   Thu, 26 Sep 2019 07:08:36 -0500
From:   Dan Murphy <dmurphy@...com>
To:     Pavel Machek <pavel@....cz>
CC:     <jacek.anaszewski@...il.com>, <linux-leds@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linus.walleij@...aro.org>,
        <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Tony Lindgren <tony@...mide.com>,
        Benoît Cousson <bcousson@...libre.com>
Subject: Re: [PATCH v9 01/15] leds: multicolor: Add sysfs interface definition

Pavel

On 9/26/19 6:10 AM, Pavel Machek wrote:
> Hi!
>
>> diff --git a/Documentation/leds/leds-class-multicolor.rst b/Documentation/leds/leds-class-multicolor.rst
>> new file mode 100644
>> index 000000000000..87a1588d7619
>> --- /dev/null
>> +++ b/Documentation/leds/leds-class-multicolor.rst
>> @@ -0,0 +1,96 @@
>> +====================================
>> +Multi Color LED handling under Linux
>> +====================================
>> +
>> +Description
>> +===========
>> +The multi color class groups monochrome LEDs and allows controlling two
>> +aspects of the final combined color: hue and lightness. The former is
>> +controlled via <color>_intensity files and the latter is controlled
>> +via brightness file.
>> +
>> +For more details on hue and lightness notions please refer to
>> +https://en.wikipedia.org/wiki/CIECAM02.
>> +
>> +Note that intensity files only cache the written value and the actual
>> +change of hardware state occurs upon writing brightness file. This
>> +allows for changing many factors of the perceived color in a virtually
>> +unnoticeable way for the human observer.
> So unlike previous versions, userspace will need to write 4 files
> instead of one in the common case.

Request was made here in v5 of the patchset

https://lore.kernel.org/patchwork/patch/1126685/


>
>> +Directory Layout Example
>> +========================
>> +root:/sys/class/leds/rgb:grouped_leds# ls -lR colors/
>> +-rw-rwxr-- 1 root root 4096 Jul 7 03:10 red_max_intensity
>> +--w--wx-w- 1 root root 4096 Jul 7 03:10 red_intensity
>> +-rw-rwxr-- 1 root root 4096 Jul 7 03:10 green_max_intensity
>> +--w--wx-w- 1 root root 4096 Jul 7 03:10 green_intensity
>> +-rw-rwxr-- 1 root root 4096 Jul 7 03:10 blue_max_intensity
>> +--w--wx-w- 1 root root 4096 Jul 7 03:10 blue_intensity
> Permissions are way off here.
Yes Jacek made a comment in the code about octals.
>
>> +A user first writes the color LED brightness file with the brightness level that
>> +is necessary to achieve a blueish violet output from the RGB LED group.
>> +
>> +echo 138 > /sys/class/leds/rgb:grouped_leds/red_intensity
>> +echo 43 > /sys/class/leds/rgb:grouped_leds/green_intensity
>> +echo 226 > /sys/class/leds/rgb:grouped_leds/blue_intensity
> No, you can't tell what kind of color this will result in.

I tested this combination on two devices (LP5523 and LP50xx) and it was 
a blueish violet.

> Will you be on ELCE/OSS in Lyon?

Unfortunately no.

Dan

>
> Best regards,
> 									Pavel
>