Re: [PATCH v7 1/5] leds: core: add generic support for RGB LED's

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Hi Karl,

On 03/06/2016 09:55 PM, Karl Palsson wrote:
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Heiner Kallweit <hkallweit1@xxxxxxxxx> wrote:
Add generic support for RGB LED's.

Basic idea is to use enum led_brightness also for the hue and
saturation color components.This allows to implement the color
extension w/o changes to struct led_classdev.

Select LEDS_RGB to enable building drivers using the RGB
extension.

Flag LED_SET_HUE_SAT allows to specify that hue / saturation
should be overridden even if the provided values are zero.

Some examples for writing values to
/sys/class/leds/<xx>/brightness: (now also hex notation can be
used)

255 -> set full brightness and keep existing color if set 0 ->
switch LED off but keep existing color so that it can be
restored
      if the LED is switched on again later
0x1000000 -> switch LED off and set also hue and saturation to
0 0x00ffff -> set full brightness, full saturation and set hue
to 0 (red)



I admit I hadn't seen this earlier, and I didn't spend all day
looking at previous attempts, but what's the motivation for
putting all this overloaded syntax into the "brightness" file? I
thought the point was to have a single value in each file, one of
the references I did find was

With single value per file there would be problems with colour
components setting synchronization.

http://www.spinics.net/lists/linux-leds/msg02995.html Is there
some thread where this was decided as advantageous? Surely 0-255
for _brightness_ is what the brightness entry should do?

You can find a reference to the related discussion in [1].

I'd like to set the rgb colour of a led (or hsv, that can be it's
own file too) and separately ramp the brightness up and down. I
also think it's substantially simpler and easier to use from the
user's point of view, which is surely the place you want easy
right?

I'm also not very keen on overloading the brightness attribute
semantics. Nonetheless it seems impossible to add support for
setting three colour components otherwise than through a single
syscall, if we want to make it synchronous and compatible with
LED triggers.

HSV color scheme is also very convenient for adapting monochrome
brightness semantics to the RGB realm.


[1] http://www.spinics.net/lists/linux-leds/msg05477.html

--
Best regards,
Jacek Anaszewski
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