linux-kernel - Re: [PATCH v3] iio: adc: Add support for TI ADC108S102 and ADC128S102

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Date:   Fri, 05 May 2017 23:32:03 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Jan Kiszka <jan.kiszka@...mens.com>,
        Jonathan Cameron <jic23@...nel.org>
Cc:     linux-iio@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sascha Weisenberger <sascha.weisenberger@...mens.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v3] iio: adc: Add support for TI ADC108S102 and
 ADC128S102

On Fri, 2017-05-05 at 22:09 +0200, Jan Kiszka wrote:
> On 2017-05-05 20:52, Jonathan Cameron wrote:
> > On 05/05/17 11:39, Jan Kiszka wrote:
> > > On 2017-05-05 11:54, Andy Shevchenko wrote:
> > > > On Fri, 2017-05-05 at 08:31 +0200, Jan Kiszka wrote:

>>>>> +			if (st->reg)
> > > > > +				*val =
> > > > > regulator_get_voltage(st->reg) 
> > > > > / 1000;
> > > > > +			else
> > > > > +				*val = st->va_millivolt;
> > > > > +
> > > > 
> > > > Another way is to not just hard code the value, but create a
> > > > fixed
> > > > voltage regulator out of it. In this case you will have one way
> > > > to get
> > > > its value.
> > > 
> > > That's a good idea.
> > 
> > Agreed. Make sure to cc Mark Brown though as I'll need an ack from
> > him
> > to have a fixed reg hiding in here.
> 
> After diving deeper, it not longer appears to be a good idea:
> 
> - pulls in a non-obvious requirement for CONFIG_REGULATOR on platforms
>   that otherwise do not need it

Why is it a problem?

> - requires complex life-cycle management so that the fixed regulator
> is
>   instantiated on the first device creation and removed with the last
>   one

Who cares if you register more than one?

> We better go with the static value assignment.
> 
> I'll move that regulator_get_voltage into the probing function which
> will simplify things further (va_millivolt will carry the value for
> both
> cases).

Yes, it would be the way, if system has it's fixed.

But in this case you need to threat regulator as optional if we are
going to enable/disable them for PM.

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy