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

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Message-ID: <545A2EDB.5040801@kernel.org>
Date:	Wed, 05 Nov 2014 14:06:19 +0000
From:	Jonathan Cameron <jic23@...nel.org>
To:	"Ivan T. Ivanov" <iivanov@...sol.com>
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 05/11/14 13:57, Ivan T. Ivanov wrote:
> 
> 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().
Good point on grnd, but vref is set but never read anywhere that I can find..

> 
>>
>>> + * @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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