linux-kernel - Re: [PATCH ] leds: add new transient trigger for one shot timer support

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Message-ID: <1335219745.2850.7.camel@lorien2>
Date:	Mon, 23 Apr 2012 16:22:25 -0600
From:	Shuah Khan <shuahkhan@...il.com>
To:	NeilBrown <neilb@...e.de>, Jonas Bonn <jonas@...thpole.se>
Cc:	shuahkhan@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Richard Purdie <richard.purdie@...uxfoundation.org>
Subject: Re: [PATCH ] leds: add new transient trigger for one shot timer
 support

On Mon, 2012-04-23 at 15:45 +1000, NeilBrown wrote:
> On Mon, 23 Apr 2012 07:29:59 +0200 Jonas Bonn <jonas@...thpole.se> 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).
> 
Neil/Jonas,

Thanks for a good discussion and ideas. Are you okay with supporting the
following use-case as a first cut implementation and see how that works
and then add brightness adjustment later?

echo transient > trigger
echo 200 > duration
echo 1 > activate

I am taking a look at "safe_delay_show" and "safe_delay_store" in
drivers/md/md.c. I think I can easily change what I have now to do what
these routines do. i.e going with seconds as units based on Neil's
suggestion.

I did make the change to name the properties duration and activate,
dropping the transient pre-fix on both properties.

Thanks,
-- Shuah

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