Re: best way to handle LEDs

[Robert Schwebel <r.schwebel@pengutronix.de>]

On Wed, Nov 02, 2005 at 12:44:59AM +0100, Pavel Machek wrote:
> Handheld machines have limited number of software-controlled status
> LEDs. Collie, for example has two of them; one is labeled "charge" and
> second is labeled "mail".
> 
> At least the "mail" led should be handled from userspace, and it would
> be nice if (at least) different speeds of blinking could be used --
> original Sharp ROM uses at least:
> 
> yellow off: 	not charging
> yellow on:	charging
> yellow fast blink: charge error
> 
> I think even slow blinking was used somewhere. I have some code from
> John Lenz (attached); it uses sysfs interface, exports led collor, and
> allows setting different frequencies.
> 
> Is that acceptable, or should some other interface be used?

IMHO reducing digital outputs to LEDs goes not far enough. All System-
on-Chip CPUs have General Purpose I/O pins today, which can act as
inputs or outputs and may be used for LEDs, matrix keyboard lines, we
even use them as shutdown lines for DC/DC converters in Linux based
power controllers for autonomous measurement systems. I think a
framework for LEDs should be based upon a low level infrastrucutre for
GPIOs. I've written such a thing some time ago, it has been discussed in 

http://marc.theaimsgroup.com/?l=linux-kernel&m=109419621428925&w=2

Unfortunately, I didn't have time to take care of that stuff yet and
port them to recent kernels :-( 

Robert
-- 
 Dipl.-Ing. Robert Schwebel | http://www.pengutronix.de
 Pengutronix - Linux Solutions for Science and Industry
   Handelsregister:  Amtsgericht Hildesheim, HRA 2686
     Hannoversche Str. 2, 31134 Hildesheim, Germany
   Phone: +49-5121-206917-0 |  Fax: +49-5121-206917-9

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/