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

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Message-ID: <20150127194447.GO7200@lukather>
Date:	Tue, 27 Jan 2015 20:44:47 +0100
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Hans de Goede <hdegoede@...hat.com>
Cc:	Priit Laes <plaes@...es.org>, linux-sunxi@...glegroups.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, Jan 27, 2015 at 11:52:34AM +0100, Hans de Goede wrote:
> Hi,
> 
> On 27-01-15 10:49, 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@...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.
> 
> The android driver always uses 0.2V / 200mV steps, so what I do is
> simply create a mapping with 200mV mapped to KEY_VOLUMEUP, 400mV mapped
> to KEY_VOLUMEDOWN, etc. following the hardcoded android driver mapping:
> 
> https://github.com/linux-sunxi/linux-sunxi/blob/sunxi-3.4/drivers/input/keyboard/sun4i-keyboard.c#L136
> 
> Usually this will be correct in one go, after testing one can shuffle
> key codes as needed (usually not needed) and/or remove unused entries.
> 
> With that said I do think that a sysfs file to see the actual voltages,
> or a kernel parameter to printk them on keypress interrupt would be useful.
> 
> I guess the printk option would be better as it would show the actual
> keypress value read, not some semi-random sample.

That wouldn't require that much code actually. Either using dev_dbg,
or debugfs like Dmitry was suggesting would be two nice solutions I
guess.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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