Re: [PATCH] iio: adc: ad799x: Implement selecting external reference voltage input on AD7991, AD7995 and AD7999.

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 30 Aug 2021 16:59:34 +0200
Florian Boor <florian.boor@kernelconcepts.de> wrote:

> Make use of the AD7991_REF_SEL bit and support using the external
> reference voltage by setting the 'vref-external' property in devicetree.
> 
> Signed-off-by: Florian Boor <florian.boor@kernelconcepts.de>

Normal convention on this (not helped here by the complete lack of
a binding document for this device) would be that the driver would
use the external vref is vref-supply is present.

Currently the driver uses devm_regulator_get().  In this case it
should be using devm_regulator_get_optional() as that will avoid a
'fake' regulator being provided.  

The driver will need a few changes to handle the possible error return
from that call, but it shouldn't be too complicated.

If you are willing it would be great to have a binding description for
this driver. I'm no sure how it has slipped through the net for so long!

Jonathan

> ---
>  drivers/iio/adc/ad799x.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/ad799x.c b/drivers/iio/adc/ad799x.c
> index 18bf8386d50a..3ae7ec72caa3 100644
> --- a/drivers/iio/adc/ad799x.c
> +++ b/drivers/iio/adc/ad799x.c
> @@ -770,6 +770,7 @@ static int ad799x_probe(struct i2c_client *client,
>  				   const struct i2c_device_id *id)
>  {
>  	int ret;
> +	int extra_config = 0;
>  	struct ad799x_state *st;
>  	struct iio_dev *indio_dev;
>  	const struct ad799x_chip_info *chip_info =
> @@ -806,6 +807,17 @@ static int ad799x_probe(struct i2c_client *client,
>  	if (ret)
>  		goto error_disable_reg;
>  
> +
> +	/* allow to use external reference voltage */
> +	if ((st->id == ad7991) || (st->id == ad7995) || (st->id == ad7999)) {
> +		unsigned int vref_external = 0;
> +	        of_property_read_u32(client->dev.of_node, "vref-external",
> +			&vref_external);
> +
> +		if (vref_external)
> +			extra_config |= AD7991_REF_SEL;
> +	}
> +
>  	st->client = client;
>  
>  	indio_dev->name = id->name;
> @@ -815,7 +827,7 @@ static int ad799x_probe(struct i2c_client *client,
>  	indio_dev->channels = st->chip_config->channel;
>  	indio_dev->num_channels = chip_info->num_channels;
>  
> -	ret = ad799x_update_config(st, st->chip_config->default_config);
> +	ret = ad799x_update_config(st, st->chip_config->default_config | extra_config);
>  	if (ret)
>  		goto error_disable_vref;
>