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

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Message-ID: <20250412124229.7917e2df@jic23-huawei>
Date: Sat, 12 Apr 2025 12:42:29 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: David Lechner <dlechner@...libre.com>
Cc: Matti Vaittinen <mazziesaccount@...il.com>, 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 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 :)

Jonathan



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