linux-kernel - Re: [PATCH 2/2] iio: afe: unit-converter: add support for adi,lt6106

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Message-ID: <c2923ac0-5e28-eef0-e32a-1e25ce550a82@ti.com>
Date:   Thu, 12 Apr 2018 10:35:57 -0500
From:   "Andrew F. Davis" <afd@...com>
To:     Peter Rosin <peda@...ntia.se>,
        Lars-Peter Clausen <lars@...afoo.de>,
        <linux-kernel@...r.kernel.org>
CC:     Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Fabio Estevam <festevam@...il.com>,
        <linux-iio@...r.kernel.org>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH 2/2] iio: afe: unit-converter: add support for adi,lt6106

On 04/12/2018 09:29 AM, Peter Rosin wrote:
> On 2018-04-11 18:13, Andrew F. Davis wrote:
>> On 04/11/2018 10:51 AM, Lars-Peter Clausen wrote:
>>> On 04/11/2018 05:43 PM, Andrew F. Davis wrote:
>>>> On 04/11/2018 09:15 AM, Peter Rosin wrote:
>>>>> This is a current sense amplifier from Analog Devices.
>>>>>
>>>>> Signed-off-by: Peter Rosin <peda@...ntia.se>
>>>>> ---
>>>>>  drivers/iio/afe/Kconfig              |  3 +-
>>>>>  drivers/iio/afe/iio-unit-converter.c | 54 ++++++++++++++++++++++++++++++++++++
>>>>>  2 files changed, 56 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/iio/afe/Kconfig b/drivers/iio/afe/Kconfig
>>>>> index 642ce4eb12a6..0e10fe8f459a 100644
>>>>> --- a/drivers/iio/afe/Kconfig
>>>>> +++ b/drivers/iio/afe/Kconfig
>>>>> @@ -10,7 +10,8 @@ config IIO_UNIT_CONVERTER
>>>>>  	depends on OF || COMPILE_TEST
>>>>>  	help
>>>>>  	  Say yes here to build support for the IIO unit converter
>>>>> -	  that handles voltage dividers and current sense shunts.
>>>>> +	  that handles voltage dividers, current sense shunts and
>>>>> +	  the LT6106 Current Sense Amplifier from Analog Devices.
>>>>
>>>> Could work better to split these out into separate drivers. Maybe a
>>>> iio-shunt-resistor.c that does just voltage->current with the
>>>> appropriate scaling. Then make a a separate lt6106.c.
>>>
>>> I don't think we need a separate driver here. There are tons of circuits
>>> that all work the same way and all require the same properties. If we'd add
>>> a driver for each of them we'd get buried in boilerplate code.
>>>
>>
>> Fair enough, then it should at least be renamed to something generic
>> like current-sense-amplifier, as you said lots of circuits do this, not
>> just lt6106s. We will have then have support for:
>>
>> current-sense-amplifier
>> current-sense-shunt
>> voltage-divider
> 
> For the compatible "current-sense-amplifier", I would advocate the
> properties...
> 
>  sense-resistor-micro-ohms
>  sense-gain
> 
> (or something close to that)
> 
> ...and not input-resistor-ohms and output-resistor-ohms which are way
> more particular to the LT6106.
> 
> But as I said in the cover letter, I didn't go with sense-gain since I
> thought I would end up with requests for non-integer gains. There is
> yet to be a comment on the non-integer gain problem, and before there
> is a path forward for that case, I'm reluctant.
> 

Why not similar to what you had before with the resistor:

sense-gain-multiplier
sense-gain-divider

if either are missing assume they are 1.

>> compatibles in this driver called "unit-converter" which is still a
>> misnomer IMHO.
> 
> I don't remember you having presented your preference, and I think
> that goes against the established bike-shedding protocol?
> 

True, how about "current-sense-from-voltage" ?

Andrew

> Cheers,
> Peter
>