Re: RGB LED control (was Re: "advanced" LED controllers)

["Måns Rullgård" <mans@mansr.com>]

Geert Uytterhoeven <geert@linux-m68k.org> writes:

> Hi Pavel,
>
> On Sun, Mar 8, 2015 at 9:57 PM, Pavel Machek <pavel@ucw.cz> wrote:
>> Ok, so I played with RGB LED a bit, and we have quite a gap in
>> documentation: what 50% brightness means is non-trivial and very
>> important in case we want to do smooth blinking and color transitions.
>>
>> Signed-off-by: Pavel Machek <pavel@ucw.cz>
>>
>> diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led
>> index 3646ec8..649d7a6 100644
>> --- a/Documentation/ABI/testing/sysfs-class-led
>> +++ b/Documentation/ABI/testing/sysfs-class-led
>> @@ -8,6 +8,11 @@ Description:
>>                 non-zero brightness settings. The value is between 0 and
>>                 /sys/class/leds/<led>/max_brightness.
>>
>> +               If LED supports continuous brightness settings, 50% brightness
>> +               should correspond to 50% brightness perceived by human, in a similar
>> +               manner pixel brightness on monitor does (not 50% PWM).
>
> How many drivers do it right? How many don't?
>
> For those that don't, perhaps we handle the conversion between perceived and
> pwm in the core, e.g. by adding a new flag to led_classdev.flags to indicate
> the need for conversion?

Some LED controllers do the right thing in hardware, so any adjustment
done in the core needs to be optional.

-- 
Måns Rullgård
mans@mansr.com