linux-kernel - Re: [PATCH 2/2] leds: Support OpenFirmware led bindings

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Message-ID: <20080728184955.GB21874@secretlab.ca>
Date:	Mon, 28 Jul 2008 12:49:55 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Trent Piepho <tpiepho@...escale.com>
Cc:	Anton Vorontsov <avorontsov@...mvista.com>,
	linux-kernel@...r.kernel.org, Richard Purdie <rpurdie@...ys.net>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Kumar Gala <galak@...nel.crashing.org>, linuxppc-dev@...abs.org
Subject: Re: [PATCH 2/2] leds: Support OpenFirmware led bindings

On Mon, Jul 28, 2008 at 11:26:28AM -0700, Trent Piepho wrote:
> On Mon, 28 Jul 2008, Anton Vorontsov wrote:
> > On Mon, Jul 28, 2008 at 11:09:14AM -0600, Grant Likely wrote:
> > [...]
> >>>>> +- function :  (optional) This parameter, if present, is a string
> >>>>> +  defining the function of the LED.  It can be used to put the LED
> >>>>> +  under software control, e.g. Linux LED triggers like "heartbeat",
> >>>>> +  "ide-disk", and "timer".  Or it could be used to attach a hardware
> >>>>> +  signal to the LED, e.g. a SoC that can configured to put a SATA
> >>>>> +  activity signal on a GPIO line.
> >>>>
> >>>> This makes me nervous.  It exposes Linux internal implementation details
> >>>> into the device tree data.  If you want to have a property that
> >>>> describes the LED usage, then the possible values and meanings should be
> >>>> documented here.
> >>>
> >>> Should it be a linux specific property then?  I could list all the current
> >>> linux triggers, but enumerating every possible function someone might want
> >>> to assign to an LED seems hopeless.
> >>
> >> I'd rather see the device tree provide 'hints' toward the expected usage
> >> and if a platform needs something specific, then the platform specific
> >> code should setup the trigger.
> >>
> > Maybe we can encode leds into devices themselves, via phandles?
> 
> How will this work for anything besides ide activity?  For example, flashing,
> heartbeat, default on, overheat, fan failed, kernel panic, etc.

It certainly doesn't work for everything; but where it does work it
makes a lot of sense because the property position provides a lot of
context.

> 
> > And then the OF GPIO LEDs driver could do something like:
> >
> > char *ide_disk_trigger_compatibles[] = {
> > 	"fsl,sata",
> > 	"ide-generic",
> > 	...
> > };
> 
> Everytime someone added a new ide driver, this table would have to be updated.

Yes, the implementation needs thought.

g.
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