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

[Jacek Anaszewski]

On 04/09/2016 06:01 PM, Pavel Machek wrote:
> Hi!
>
> > > > > What's tricky about patterns is that you need to control 3 (or more)
> > > > > leds at a time. Problem you are trying to solve here is ... control of
> > > > > 3 leds, at the same time.
> > > > >
> > > > > So let's solve them together.
> > > >
> > > > OK, now I've got your point. So we'd need to have a means for defining
> > > > patterns. The interface could be located at /sys/class/leds/patterns.
> > > >
> > > > We'd need to have a flexible way for defining LED class devices involved
> > > > in a pattern. Since we cannot guarantee no space in a LED class device
> > > > name, then a single attribute containing space separated list is not an
> > > > option. We'd have to create a predefined set of attributes that would
> > > > contain LED class device name. Predefined implies that it would be
> > > > a fixed number, i.e. either some attributes would always remain unused
> > > > or, which is even worse, we could run out of free attributes for some
> > > > use cases.
> > >
> > > There's a better solution: make pattern behave as a trigger for leds
> > > it controls.
> > >
> > > So we'd have
> > >
> > > /sys/class/leds/patterns/lp5523
> > >
> > > then we'd have
> > >
> > > /sys/class/leds/lp5523::red/trigger = "lp5523:1"
> > > /sys/class/leds/lp5523::green/trigger = "lp5523:2"
> > > /sys/class/leds/lp5523::blue/trigger = "lp5523:3"
> > >
> > > (or something similar, I'd have to boot the n900 to see the exact
> > > names).
> >
> > How about implementing patterns as a specific typer of triggers?
> > Let's say we have ledtrig-rgb-pattern:
>
> Well, we'd need ledtrig-rgb-pattern-1, ledtrig-rgb-pattern-2, ... , as we
> can have more than one rgb led. But yes.

Triggers can have many listeners, i.e. led_trigger_event() sets
brightness on all LED class devices registered on given trigger.
We could have led_trigger_rgb_event() that would set brightness
on all groups-of-three LEDs registered on given rgb-trigger.

I agree that ledtrig-rgb-pattern-1, ledtrig-rgb-pattern-2, etc. would
be also needed to add a capability of setting different colors on
different LED devices.

> > After setting a trigger following sysfs attribute would appear
> > in a LED class device sysfs interface:
> >
> > $cat /sys/class/lp5523::red/rgb_color
> > red green blue [none]
> >
> > $echo "red" > /sys/class/leds/lp5523::red/rgb_color
> >
> > and similarly
> >
> > $echo "green" > /sys/class/leds/lp5523::green/rgb_color
> > $echo "blue" > /sys/class/leds/lp5523::blue/rgb_color
>
> Yes, that would work -- selecting channels from the pattern.
>
> > Similar approach could be applied for blink patterns:
> > There could be additional attributes provided for defining
> > the position in a blink sequence, or/and blink period.
>
> For patterns, I'd suggest array of (r g b time) values.
>
> Pattern engines can do stuff like "slowly turn LED from off to red, then switch color to
> white, then slowly turn it to yellow, then turn it off at once" with defined speeds
> for "slowly" and option of either linear on non-linear brightness ramping.
>
> The last option might be a bit too much, but I believe we should support the rest.

Yes, that's an interesting idea. It also turns out that trigger based
patterns could be also used for defining generic patterns for a group
of monochrome LEDs.

--
Best regards,
Jacek Anaszewski