linux-kernel - Re: [linux-sunxi] Re: [PATCH] arm: sunxi: input: RFC: Add sysfs voltage for sun4i-lradc driver

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Date:	Tue, 27 Jan 2015 11:49:49 +0200
From:	Priit Laes <plaes@...es.org>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	linux-sunxi@...glegroups.com, Hans de Goede <hdegoede@...hat.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-input@...r.kernel.org
Subject: Re: [linux-sunxi] Re: [PATCH] arm: sunxi: input: RFC: Add sysfs
 voltage for sun4i-lradc driver


On Tue, 2015-01-27 at 10:18 +0100, Maxime Ripard wrote:
> Hi,
> 
> On Mon, Jan 26, 2015 at 06:58:32PM +0200, Priit Laes wrote:
> > ---
> 
> Like Hans was pointing out, commit log and signed-off-by please
> 
> >  .../ABI/testing/sysfs-driver-input-sun4i-lradc     |  4 ++
> >  drivers/input/keyboard/sun4i-lradc-keys.c          | 49 
> > +++++++++++++++++-----
> >  2 files changed, 43 insertions(+), 10 deletions(-)
> >  create mode 100644 Documentation/ABI/testing/sysfs-driver-input-
> > sun4i-lradc
> > 
> > diff --git a/Documentation/ABI/testing/sysfs-driver-input-sun4i-
> > lradc b/Documentation/ABI/testing/sysfs-driver-input-sun4i-lradc
> > new file mode 100644
> > index 0000000..e4e6448
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-driver-input-sun4i-lradc
> > @@ -0,0 +1,4 @@
> > +What:          /sys/class/input/input(x)/device/voltage
> > +Date:          February 2015
> > +Contact:       Priit Laes <plaes@...es.org>
> > +Description:   ADC output voltage in microvolts or 0 if device is 
> > not opened.
> 
> Why is it returning 0 when "device is not opened" ? What does that 
> even mean? You can't read that file without opening it.

It means that something has to open the /dev/input/inputX device which 
sets up the ADC before the voltage can be read from the sysfs file.

[...]


> 
> As I told you already, if you're going to expose this an ADC in the 
> end, the proper solution is to use the IIO framework, not adding a 
> custom sysfs file.

My intention was to expose just a simple debug output, so one can 
press the buttons and read the voltages for devicetree keymap.

If anyone can suggest a simpler approach than current sysfs based one, 
I would do it. But full blown iio driver is currently out of scope. 
Also, Carlo's (ccaione) initially submitted (?) driver for lradc 
utilized iio subsystem.

Päikest,
Priit :)
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