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

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Message-ID: <545A42FA.7090501@kernel.org>
Date:	Wed, 05 Nov 2014 15:32:10 +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 15:01, Ivan T. Ivanov wrote:
> 
> On Wed, 2014-11-05 at 14:06 +0000, Jonathan Cameron wrote:
>> 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..
>>
> 
> Right. At this point it is not used. Driver right now provide basic per
> channel voltage measurements. The plan is to add temperature compensation for the
> measurements and additional scaling functions which are specific per channel.
> 
> I could drop this field from initial driver version if you like.
Probably best as otherwise some compiler in a clever mood will give
a warning and I'll get an irritating patch to remove it!

J
> 
> Regards,
> Ivan
> 
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