linux-kernel - Re: [PATCH 3/5] iio: addac: ad74413r: implement support for optional refin-supply

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Date:   Sat, 12 Nov 2022 16:56:49 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Cosmin Tanislav <cosmin.tanislav@...log.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] iio: addac: ad74413r: implement support for
 optional refin-supply

On Fri, 11 Nov 2022 15:39:19 +0100
Rasmus Villemoes <linux@...musvillemoes.dk> wrote:

> The ad74412r/ad74413r has an internal 2.5V reference output, which (by
> tying the REFOUT pin to the REFIN pin) can be used in lieu of an
> external 2.5V input reference.
> 
> Support that case by using devm_regulator_get_optional(), and simply
> hardcode the 2500000 uV in ad74413r_get_output_current_scale().
> 
> I'm not sure this is completely correct, but it's certainly better
> than the current behaviour, where when refin-supply is not defined in
> device tree, the regulator framework helpfully does its
> 
>   supply refin not found, using dummy regulator

You could reasonably assume that's a bug in the firmware.. See suggestions
in reply to patch 2.  Given external wiring is involved, I don't think
we can assume absence of a regulator means that loop back is in place.
We need to indicate that explicitly in the binding in some way.

Jonathan


> 
> thing. When we then do the regulator_get_voltage(), that dummy
> regulator of course doesn't support that operation and thus returns
> -22 (-EINVAL) which is used without being checked.
> 
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
>  drivers/iio/addac/ad74413r.c | 31 ++++++++++++++++++++-----------
>  1 file changed, 20 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/iio/addac/ad74413r.c b/drivers/iio/addac/ad74413r.c
> index 37485be88a63..9f77d2f514de 100644
> --- a/drivers/iio/addac/ad74413r.c
> +++ b/drivers/iio/addac/ad74413r.c
> @@ -608,7 +608,10 @@ static int ad74413r_get_output_voltage_scale(struct ad74413r_state *st,
>  static int ad74413r_get_output_current_scale(struct ad74413r_state *st,
>  					     int *val, int *val2)
>  {
> -	*val = regulator_get_voltage(st->refin_reg);
> +	if (st->refin_reg)
> +		*val = regulator_get_voltage(st->refin_reg);
> +	else
> +		*val = 2500000;
>  	*val2 = st->sense_resistor_ohms * AD74413R_DAC_CODE_MAX * 1000;
>  
>  	return IIO_VAL_FRACTIONAL;
> @@ -1313,19 +1316,25 @@ static int ad74413r_probe(struct spi_device *spi)
>  	if (IS_ERR(st->regmap))
>  		return PTR_ERR(st->regmap);
>  
> -	st->refin_reg = devm_regulator_get(st->dev, "refin");
> -	if (IS_ERR(st->refin_reg))
> -		return dev_err_probe(st->dev, PTR_ERR(st->refin_reg),
> -				     "Failed to get refin regulator\n");
> +	st->refin_reg = devm_regulator_get_optional(st->dev, "refin");
> +	if (IS_ERR(st->refin_reg)) {
> +		ret = PTR_ERR(st->refin_reg);
> +		if (ret != -ENODEV)
> +			return dev_err_probe(st->dev, ret,
> +					     "Failed to get refin regulator\n");
> +		st->refin_reg = NULL;
> +	}
>  
> -	ret = regulator_enable(st->refin_reg);
> -	if (ret)
> -		return ret;
> +	if (st->refin_reg) {
> +		ret = regulator_enable(st->refin_reg);
> +		if (ret)
> +			return ret;
>  
> -	ret = devm_add_action_or_reset(st->dev, ad74413r_regulator_disable,
> +		ret = devm_add_action_or_reset(st->dev, ad74413r_regulator_disable,
>  				       st->refin_reg);
> -	if (ret)
> -		return ret;
> +		if (ret)
> +			return ret;
> +	}
>  
>  	st->sense_resistor_ohms = 100000000;
>  	device_property_read_u32(st->dev, "shunt-resistor-micro-ohms",