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

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Message-ID: <78d17b05-3f0d-4903-afe3-8051d4bd051d@baylibre.com>
Date: Fri, 11 Apr 2025 08:34:42 -0500
From: David Lechner <dlechner@...libre.com>
To: Matti Vaittinen <mazziesaccount@...il.com>,
 Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
Cc: Jonathan Cameron <jic23@...nel.org>, 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 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).

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