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

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Date:   Sun, 7 May 2017 12:19:22 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jan Kiszka <jan.kiszka@...mens.com>
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>, Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>
Subject: Re: [PATCH v3] iio: adc: Add support for TI ADC108S102 and ADC128S102

On 05/05/17 21:32, Andy Shevchenko wrote:
> 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?
It seems unlikely this is the first ever case of needing proper
regulator support on ACPI platforms.  Mark/Liam, an precedents that you
know of?
> 
>> - 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.
>