Re: [PATCH ] leds: add new transient trigger for one shot timersupport

From: NeilBrown
Date: Mon Apr 23 2012 - 01:45:51 EST

On Mon, 23 Apr 2012 07:29:59 +0200 Jonas Bonn <jonas@xxxxxxxxxxxx> wrote:

> On Mon, 2012-04-23 at 11:56 +1000, NeilBrown wrote:
> > I wonder if we should allow control of the brightness during the "on" time as
> > well.
> > You could set the brightness after enabling the timer, but awkward pauses or
> > races could then leave the "led" permanently on.
> echo transient > trigger
> echo 200 > duration
> echo 1 > activate
context switch - lots of IO - time passes, 200ms or more, led gets turned of
and then back to:
> echo 100 > brightness

led gets turned on and there is nothing to turn it off.

Not a likely case I agree, but not impossible.

The problem is that just setting the brightness will turn the led on
independent of the start of the trigger (unless you set the brightness to 0 -
that disables the trigger).


> Worst case, the brightness doesn't get set and you get a 'bright' LED
> until it expires... but at least it does expire!
> >
> > Possibly we could hook into led_set_brightness() and restart the timer
> > whenever the brightness was set - and remember the setting.
> An easy way to do this might be to check the brightness setting at the
> time the timer expires and save this value. Next time the LED is
> activated, we use this brightness setting instead of FULL_ON. It would
> be nice to keep this trigger self-contained and not have to hook into
> led_set_brightness
> You make interesting point about using the brightness property as the
> actual timer trigger, though. That's pretty elegant, but it does
> require hooking into led_set_brightness.
> /Jonas

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