linux-kernel - Re: [PATCH v2 0/2] iio: add unit converter

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Date:   Tue, 10 Apr 2018 08:06:52 -0500
From:   Rob Herring <robh@...nel.org>
To:     Peter Rosin <peda@...ntia.se>
Cc:     "Andrew F. Davis" <afd@...com>, linux-kernel@...r.kernel.org,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Mark Rutland <mark.rutland@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Michael Hennerich <michael.hennerich@...log.com>,
        Phil Reid <preid@...ctromag.com.au>, linux-iio@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v2 0/2] iio: add unit converter

On Tue, Apr 03, 2018 at 08:09:08PM +0200, Peter Rosin wrote:
> On 2018-04-03 19:41, Andrew F. Davis wrote:
> > On 04/03/2018 10:36 AM, Peter Rosin wrote:
> >> Hi!
> >>
> >> This driver implements support for voltage dividers and current
> >> sense circuits. It's pretty generic and should be easily adaptable
> >> to other linear scaling purposes...
> >>
> > 
> > I really like this idea, defining channel scaling / channel type
> > conversion in DT will be very useful. So much so that I would recommend
> > this not be a use specific driver but instead moved into the IIO core.
> > 
> > This would allow defining these channel conversions in the device node
> > itself, so as to not need a separate node just for the converter (the
> > conversion is not a device and probably should not have it's own node
> > anyway). It would also help with enabling this support for buffered
> > readers/writers and not just devices only supporting _raw reads/writes.
> 
> In my case, the voltage dividers and the current sense circuit are very
> much real, and I can point my finger at them on the board. Sure, they
> are not ICs, but to not call them devices is wrong IMHO, and the ADC
> which is involved have very little to do with the voltage dividers and
> the fact that it is involved in sensing current. This is not an argument
> for not moving the functionally to the core though, but that has some
> problems AFAICT. Because you need some kind of clever and generic
> binding to make the core do its thing, and it might not be easy to come
> up with something that fits all devices? And if we do put this in the
> core, that opens the door for more complex unit converters later on
> (non-linear etc), further complicating the generic bindings.

I agree. We've learned the hard way that even things like the LED diode 
itself need to be described and not just the controller.

Rob