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

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Date:	Mon, 22 Sep 2014 01:01:12 +0000
From:	"Kim, Milo" <Milo.Kim@...com>
To:	Jonathan Cameron <jic23@...nel.org>,
	Stanimir Varbanov <svarbanov@...sol.com>
CC:	Hartmut Knaack <knaack.h@....de>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Pawel Moll <pawel.moll@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Kumar Gala <galak@...eaurora.org>,
	Mark Rutland <mark.rutland@....com>,
	Grant Likely <grant.likely@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	"Angelo Compagnucci" <angelo.compagnucci@...il.com>,
	Doug Anderson <dianders@...omium.org>,
	Fugang Duan <B38611@...escale.com>,
	"Johannes Thumshirn" <johannes.thumshirn@....de>,
	Jean Delvare <jdelvare@...e.de>,
	Philippe Reynes <tremyfr@...oo.fr>,
	Lee Jones <lee.jones@...aro.org>,
	"Josh Cartwright" <joshc@...eaurora.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"David Collins" <collinsd@...eaurora.org>,
	"Ivan T. Ivanov" <iivanov@...sol.com>
Subject: RE: [PATCH v2 1/2] iio: vadc: Qualcomm SPMI PMIC voltage ADC driver

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