Re: [PATCH v5 1/4] leds: core: add generic support for RGB Color LED's

[Jacek Anaszewski]

On 04/01/2016 03:57 PM, Pavel Machek wrote:
> Hi!
> On Wed 2016-03-30 09:57:38, Jacek Anaszewski wrote:
> > Hi Heiner and Pavel,
> >
> > On 03/29/2016 10:38 PM, Heiner Kallweit wrote:
> > > Am 29.03.2016 um 12:02 schrieb Pavel Machek:
> > > > Hi!
> > > >
> > > > First, please Cc me on RGB color support.
> > > >
> > > > > Add generic support for RGB Color 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)
> > > >
> > > > Umm, that's rather strange interface -- and three values in single sysfs
> > > > file is actually forbidden.
> > > >
> > > > Plus, it is very much unlike existing interfaces for RGB LEDs, which
> > > > we already have supported in the tree. (At least nokia N900 and Sony
> > > > motion controller already contain supported three-color LEDs).
> > > >
> > > > Now... yes, there's work to be done for the 3-color LEDs. Currently,
> > > > they are treated as three different LEDs. (Which makes some sense, you
> > > > can use "battery charging" trigger for LED, and CPU activity trigger
> > > > for green, for example). It would be good to have some kind of
> > > > grouping, so that userspace can tell "these 3 leds are actually
> > > > combined into one light".
> Hi!
>
> > > At first thanks for the review comments.
> > > Treating the three physical LEDs of a RGB LED as separate LED devices
> > > might have been implemented due to the lack of alternatives.
> > > With one trigger controlling the red LED and another controlling the green
> > > LED we may end up with a yellow light. Not sure whether this is what we want.
> > >
> > > One driver for this extension was the idea of triggers using color
> > > to visualize states etc.
> > > Therefore it's not only about userspace controlling the color.
> > > As a trigger is bound to a led_classdev we need a led_classdev
> > > representing a RGB LED device.
> > >
> > > And ok: If required the sysfs interface can be splitted into separate
> > > attributes for hue, saturation, and (existing) brightness.
> >
> > It would have the same downsides as in case of having r, g and b in
> > separate attributes, i.e. - problems with setting LED colour in
> > a consistent way. This way LED blinking in whatever colour couldn't
> > be supported reliably. It was one of your primary rationale standing
> > behind this design, if I remember correctly. Second - what about
> > triggers? We've had a long discussion about it and this design turned
> > out to be most fitting.
>
> Are on/off triggers really that useful for a LED that can produce 16
> million colors?
>
> I believe we should support patterns for RGB LEDs. Something like
> [ (time, r, g, b), ... ] . Ok, what about this one?
>
> Lets say we have
>
> /sys/class/pattern/lp5533::0
> /sys/class/pattern/software::0
>
> /sys/class/led/n900::red ; default trigger "lp5533::0:0"
> /sys/class/led/n900::green ; default trigger "lp5533::0:1"
> /sys/class/led/n900::blue ; default trigger "lp5533::0:2"
>
> Normally, pattern would correspond to one RGB LED. We could have
> attribute "/sys/class/pattern/lp5533::0/color" containing R,G,B for
> this pattern.

This involves the same issue you were opposed to: three values per
sysfs attribute.

> Then we could have normal "trigger" mechanism, working
> with the color used. Probably recognizing "none" for manual control,
> and "pattern" for pattern control. (Pattern would be controlled as
> described above).
>
> > It's hard to address these requirements by having the settings in
> > separate attributes, due to synchronization issues, and LED trigger
> > mechanism specificity.
> >
> > There is a question whether we can bend the sysfs "one value per sysfs
> > file" rule down to RGB LEDs needs.
> >
> > Of course other brilliant ideas on how to approach the problem are
> > more than expected.
>
> linux-api sounds like interesting idea, please cc me if you do that.
>
> Best regards,
> 									Pavel

--
Best regards,
Jacek Anaszewski