linux-kernel - Re: [PATCH 4/7] ARM: dts: Enable N950 keyboard sleep leds by default

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Date:	Wed, 30 Mar 2016 12:35:21 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Sebastian Reichel <sre@...nel.org>
Cc:	Pavel Machek <pavel@....cz>,
	Benoît Cousson <bcousson@...libre.com>,
	Aaro Koskinen <aaro.koskinen@....fi>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, linux-omap@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] ARM: dts: Enable N950 keyboard sleep leds by default

* Sebastian Reichel <sre@...nel.org> [160329 07:53]:
> Hi,
> 
> On Tue, Mar 29, 2016 at 12:51:28PM +0200, Pavel Machek wrote:
> > For 1-3 in the series, Acked-by: Pavel Machek <pavel@....cz>
> > 
> > > Like the Nokia N900, the N950 has leds to show
> > > the state of sys_clkreq and sys_off_mode pins.
> > > 
> > > A detailed description for the LEDs and
> > > OMAP's sleep states can be found in Tony's
> > > commit for the Nokia N900:
> > > 
> > > c1be2032f66df9e1238bd5bc4ca666de88a62abc
> > 
> > I must say I've seen it on N900, and yes, it is useful, but no, I
> > don't think this is right.
> >
> > This is not a LED. This is a interface that changes meaning of two
> > other LEDs. I guess it should go to debugfs somewhere.

Eh that sounds like a GPIO LED to me :) And it already has a
/sys/class/leds/debug interface.

The two LEDs this GPIO controls are hardwired to sys_clkreq and
sys_off_mode pins that are the control signals between the SoC
and PMIC.

In theory you could steal the sys_clkreq and sys_off_mode pins
from the PMIC at the cost of breaking PM. But I doubt anybody
wants to do that considering it's a battery operated device.

> I don't think we should diverge N900 and N950 userspace
> APIs in this regard.
> 
> Actually the correct way would be a custom trigger
> for the leds IMHO. I don't know if the led framework
> supports per led custom triggers, though.

Sure, there are something like 10 triggers already. And
you can already change them using:

echo none > /sys/class/leds/debug::sleep/trigger

That still does not change the fact that the LEDs trigger
based on the state of sys_clkreq and sys_off_mode.

Maybe I'm not following what you guys are trying to achieve
here though :) If so, please let me know.

Regards,

Tony