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SubjectRe: [linux-sunxi] Re: [PATCH] arm: sunxi: input: RFC: Add sysfs voltage for sun4i-lradc driver
On Tue, Jan 27, 2015 at 11:49:49AM +0200, Priit Laes wrote:
>
> 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@plaes.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.

I'd consider this a bug. Why someone has to use an unrelated interface for
another interface to work correctly?

>
> [...]
>
>
> >
> > 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.

For stuff like this debugfs (AKA dumping ground) is better suited as it does
not establish ABI. i

Thanks.

--
Dmitry


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