linux-kernel - Re: [PATCH RFC v3 8/8] iio: ti-adc128s052: Drop variable vref

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Message-ID: <f705fa4e-331b-46a1-9640-d33e83f7a894@gmail.com>
Date: Mon, 14 Apr 2025 09:03:06 +0300
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Jonathan Cameron <jic23@...nel.org>, David Lechner <dlechner@...libre.com>
Cc: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
 Lars-Peter Clausen <lars@...afoo.de>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Nuno Sa <nuno.sa@...log.com>,
 Javier Carrasco <javier.carrasco.cruz@...il.com>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v3 8/8] iio: ti-adc128s052: Drop variable vref

On 12/04/2025 14:42, Jonathan Cameron wrote:
> On Fri, 11 Apr 2025 08:34:42 -0500
> David Lechner <dlechner@...libre.com> wrote:
> 
>> On 4/7/25 6:37 AM, Matti Vaittinen wrote:
>>> According to Jonathan, variable reference voltages are very rare. It is
>>> unlikely it is needed, and supporting it makes the code a bit more
>>> complex.
>>>
>>> Simplify the driver and drop the variable vref support.
>>>
>>> Suggested-by: Jonathan Cameron <jic23@...nel.org>
>>> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
>>>
>>> ---
>>
>> ...
>>
>>>   static int adc128_probe(struct spi_device *spi)
>>>   {
>>>   	const struct adc128_configuration *config;
>>> @@ -183,17 +173,12 @@ static int adc128_probe(struct spi_device *spi)
>>>   	indio_dev->channels = config->channels;
>>>   	indio_dev->num_channels = config->num_channels;
>>>   
>>> -	adc->reg = devm_regulator_get(&spi->dev, config->refname);
>>> -	if (IS_ERR(adc->reg))
>>> -		return PTR_ERR(adc->reg);
>>> +	adc->vref_mv = devm_regulator_get_enable_read_voltage(&spi->dev,
>>> +							   config->refname);
>>> +	if (adc->vref_mv < 0)
>>> +		return adc->vref_mv;
>>>   
>>> -	ret = regulator_enable(adc->reg);
>>> -	if (ret < 0)
>>> -		return ret;
>>> -	ret = devm_add_action_or_reset(&spi->dev, adc128_disable_regulator,
>>> -				       adc->reg);
>>> -	if (ret)
>>> -		return ret;
>>> +	adc->vref_mv /= 1000;
>>
>> In other drivers, we've been doing:
>>
>> ret = devm_regulator_get_enable_read_voltage(...);
>> if (ret < 0)
>> 	return dev_err_probe(dev, ret, "failed to read '%s' voltage, ...);
>>
>> adc->vref_mv = ret / 1000;
>>
>> It can be easy to make a typo or forget to specify the voltage when creating
>> a .dts, so I think the error message is helpful to catch that.
>>
>> And we use ret to avoid having adc->vref_mv temporarily holding a
>> value with the wrong units (and can make it have an unsigned type).
> 
> Good idea.
> Applied patches 1-7. I did tweak this one as well but then couldn't make
> up my mind on whether to change the type of vref_mv so I'll avoid making
> a decision and will leave patch 8 for a v4 from Matti :)

Thanks for handling the 1-7 :) I'll re-spin this, but it's likely to 
take some time. I'm having 2 weeks off from work, and my motorbike and 
boat is requiring some attention ;)

I hope I have regained a lot of energy after 2 weeks ;)

> 
> Jonathan
> 
> 
> 
>>
>>>   
>>>   	if (config->num_other_regulators) {
>>>   		ret = devm_regulator_bulk_get_enable(&spi->dev,
>>
> 


Yours,
	-- Matti