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

From: Måns Rullgård
Date: Mon Mar 09 2015 - 07:51:06 EST

Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> writes:

> Hi Pavel,
> On Sun, Mar 8, 2015 at 9:57 PM, Pavel Machek <pavel@xxxxxx> 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@xxxxxx>
>> 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
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