On Tuesday 25 November 2008, Koen Kooi wrote:
>
> Op 25 nov 2008, om 21:06 heeft David Brownell het volgende geschreven:
>
> > On Tuesday 25 November 2008, Koen Kooi wrote:
> >>>
> >>> How about a standard LED driver (optionally with a brightness
> >>> control) and the newish "backlight" trigger?
> >>
> >> Does the backlight trigger hook into the backlight class?
> >
> > It doesn't seem to call backlight_device_register(), though
> > I don't know why not. It just looks like it hooks into the
> > same notification events the backlight class does.
Re "why not" ... partial answer: because it doesn't have
a way to associate itself with the panel whose backlight
it's supplying. Seems like that should be solvable.
> > If you think that's trouble, it would probably be a good
> > thing to bring that up with the author of that new trigger
> > code (drivers/leds/ledtrig-backlight.c) ... it's very new,
> > and I'd expect such userspace interface goofs still ought
> > to be fixable.
>
> Our mails on this subject crossed eachother :)
>
> Short recap: the backlight trigger is usefull for turnign on/off e.g.
> status leds at the same the the backlight goes on/off, but shouldn't
> be (ab)used for backlight control.
That's not what its Kconfig description says. So I think
that if you care about this, you should raise the issue
with someone more involved.
> Mark Brown in that thread [1] does raise an interesting use-case,
i.e [2] ... a simpler situation than we have with TWL4030,
where we have LED signals supporting
- real LEDs
* simple leds that don't really need PWM brightness
controls: Beagle LEDB == pmu_stat
* backlights which probably *do* want PWM controls: on
those two EVMs, LEDA == backlight, using more of its
peak 160 mA current draw
- general GPIO usage, where PWM capability "must not"
kick in: Beagle LEDA == nEN_USB_PWR
His comment focussed on the two "real LEDs" cases.
> since we are in the same boat. A solution is needed, but I guess the
> wolfson people can work it out :)
Or maybe the Pandora people. ;)
If they're using the LEDA or LEDB PWMs, providing and exporting
a brightness control would be easy. If they're using the other
two PWMs, it'd be more work.
- Dave
> [1] http://linux.derkeiler.com/Mailing-Lists/Kernel/2008-10/threads.html#02359
>
[2] http://linux.derkeiler.com/Mailing-Lists/Kernel/2008-10/msg02610.html
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