linux-kernel - Re: [PATCH v4 2/2] iio: vadc: Qualcomm SPMI PMIC voltage ADC driver

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Message-ID: <1415195855.3660.4.camel@mm-sol.com>
Date:	Wed, 05 Nov 2014 15:57:35 +0200
From:	"Ivan T. Ivanov" <iivanov@...sol.com>
To:	Jonathan Cameron <jic23@...nel.org>
Cc:	Hartmut Knaack <knaack.h@....de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald <pmeerw@...erw.net>,
	Stanimir Varbanov <svarbanov@...sol.com>,
	Angelo Compagnucci <angelo.compagnucci@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
	devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v4 2/2] iio: vadc: Qualcomm SPMI PMIC voltage ADC driver


On Wed, 2014-11-05 at 13:09 +0000, Jonathan Cameron wrote:
> On 03/11/14 15:24, Ivan T. Ivanov wrote:
> > From: Stanimir Varbanov <svarbanov@...sol.com>
> > 
> > The voltage ADC is peripheral of Qualcomm SPMI PMIC chips. It has
> > 15 bits resolution and register space inside PMIC accessible across
> > SPMI bus.
> > 
> > The vadc driver registers itself through IIO interface.
> > 
> > Signed-off-by: Stanimir Varbanov <svarbanov@...sol.com>
> > Signed-off-by: Ivan T. Ivanov <iivanov@...sol.com>
> Hi Ivan,
> 
> Couple of utterly tiny bits inline.  The biggest one is that
> you store some info about the calibration that you never actually
> use... Left over from some debugging perhaps?
> 
> Jonathan

<snip>

> > +
> > +/*
> > + * VADC_CALIB_ABSOLUTE: uses the 625mV and 1.25V as reference channels.
> > + * VADC_CALIB_RATIOMETRIC: uses the reference voltage (1.8V) and GND for
> > + * calibration.
> > + */
> > +enum vadc_calibration {
> > +       VADC_CALIB_ABSOLUTE = 0,
> > +       VADC_CALIB_RATIOMETRIC
> > +};
> > +
> > +/**
> > + * struct vadc_linear_graph - Represent ADC characteristics.
> > + * @dy: numerator slope to calculate the gain.
> As dy is always equal to vref-gnd you could drop it and use those
> directly...
> 
> Conversly you store vref or grnd and never use them...

I am not sure I am following you. Please take a look in 
vadc_measure_ref_points() and vadc_calibrate().

> 
> > + * @dx: denominator slope to calculate the gain.
> > + * @vref: A/D word of the voltage reference used for the channel.
> > + * @gnd: A/D word of the ground reference used for the channel.
> > + *
> > + * Each ADC device has different offset and gain parameters which are
> > + * computed to calibrate the device.
> > + */
> > +struct vadc_linear_graph {
> > +       s32 dy;
> > +       s32 dx;
> > +       s32 vref;
> > +       s32 gnd;
> > +};
> > +
> > 

Will address blank line comment.

Regards,
Ivan
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