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

From: Jonathan Cameron <jic23@kernel.org>
To: "Kim, Milo" <Milo.Kim@ti.com>, 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 Jones <lee.jones@linaro.org>,
	Josh Cartwright <joshc@codeaurora.org>,
	Stephen Boyd <sboyd@codeaurora.org>,
	David
Subject: RE: [PATCH v2 1/2] iio: vadc: Qualcomm SPMI PMIC voltage ADC driver
Date: Mon, 22 Sep 2014 07:28:06 +0100	[thread overview]
Message-ID: <541fc191.48d5440a.0986.67a4SMTPIN_ADDED_MISSING@mx.google.com> (raw)
In-Reply-To: <A874F61F95741C4A9BA573A70FE3998FBC4743E2@DQHE06.ent.ti.com>

<collinsd@codeaurora.org>,"Ivan T. Ivanov" <iivanov@mm-sol.com>
Message-ID: <4f726fe9-707e-41bd-bcc7-188516b6f47a@email.android.com>

On September 22, 2014 2:01:12 AM GMT+01:00, "Kim, Milo" <Milo.Kim@ti.com> wrote:
>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.
It should be in millivolts... See below. 
>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/.

Indeed but the value actually returned is that from iio_read_channel_processed which

calls iio_channel_read (or does application of scale locally though the effect is the same)

with the processed value. This then calls read_raw and so gets a value that should be in millivolts.

Hence the query.

Looks to me like the ADC driver has wrong scale value? 

>
>Best regards,
>Milo

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