RE: [PATCH v2 1/2] iio: vadc: Qualcomm SPMI PMIC voltage ADC driver

From: "Kim, Milo" <Milo.Kim@ti.com>
To: Jonathan Cameron <jic23@kernel.org>,
	Stanimir Varbanov <svarbanov@mm-sol.com>
Cc: Hartmut Knaack <knaack.h@gmx.de>,
	Ian Campbell <ijc+devicetree@hellion.org.uk>,
	Pawel Moll <pawel.moll@arm.com>, Rob Herring <robh+dt@kernel.org>,
	Kumar Gala <galak@codeaurora.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Grant Likely <grant.likely@linaro.org>,
	Arnd Bergmann <arnd@arndb.de>,
	"linux-arm-msm@vger.kernel.org" <linux-arm-msm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Lars-Peter Clausen <lars@metafoo.de>,
	Angelo Compagnucci <angelo.compagnucci@gmail.com>,
	Doug Anderson <dianders@chromium.org>,
	Fugang Duan <B38611@freescale.com>,
	Johannes Thumshirn <johannes.thumshirn@men.de>,
	Jean Delvare <jdelvare@suse.de>,
	Philippe Reynes <tremyfr@yahoo.fr>,
	Lee
Subject: RE: [PATCH v2 1/2] iio: vadc: Qualcomm SPMI PMIC voltage ADC driver
Date: Mon, 22 Sep 2014 01:01:12 +0000	[thread overview]
Message-ID: <A874F61F95741C4A9BA573A70FE3998FBC4743E2@DQHE06.ent.ti.com> (raw)
In-Reply-To: <541ED2C0.4040801@kernel.org>

Hello Jonathan and Stanimir,

> >> See Documentation/ABI/sysfs-bus-iio
> >> Millivolts I think... We copied hwmon where possible.
> >
> > I'm a bit confused about these units. I searched references of
> > iio_read_channel_processed() and found a few.
> >
> > The iio_hwmon expecting milivolts. On the other side lp8788-charger.c
> > registers a get_property method in charger-manager.c, which expects
> > microvolts in get_batt_uV().
> It's definitely meant to be millivolts (lifted from hwmon a while back).
> See Documentation/ABI/testing/sysfs-bus-iio
> 
> Looks like we have a bug in lp8788-charger - it might be matched with one in
> lp8788-adc, but then there will be a bug there...
> 
> Cc'd Milo Kim.

'lp8788-charger' registers not charger-manager but power-supply subsystem.
'lp8788-adc' is the IIO driver.
'lp8788-charger' is the IIO consumer of lp8788-adc.

(How to communicate between lp8788-adc and lp8788-charger)
1. Application requests vbatt(battery voltage) by accessing /sys/class/power/
2. lp8788-charger asks lp8788-adc to get converted vbatt value
3. lp8788-adc get the battery ADC from the device.
   It returns calculated micro voltage to lp8788-charger.
4. lp8788-charger reports this uV value to the application
5. Application uses uV or converts to mV or V unit. It's up to the app.

Please note that battery app accesses not /sys/bus/iio but /sys/class/power/.

Best regards,
Milo