On Tue, 19 Mar 2024 11:11:25 +0100
Julien Stephan <jstephan@xxxxxxxxxxxx> wrote:
> From: David Lechner <dlechner@xxxxxxxxxxxx>
>
> Add support for AD7383, AD7384 pseudo-differential compatible parts.
> Pseudo differential parts require common mode voltage supplies so add
> the support for them and add the support of IIO_CHAN_INFO_OFFSET to
> retrieve the offset
>
> Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx>
> Signed-off-by: Julien Stephan <jstephan@xxxxxxxxxxxx>
Hi Julien,
A few aditional comments inline. The one about
optional regulators may be something others disagree with.
Mark, perhaps you have time to comment.
Is this usage of devm_regulator_get_optional() to check a real regulator
is supplied (as we are going to get the voltage) sensible? Feels wrong
given the regulator is the exact opposite of optional.
Jonathan
> struct ad7380_state {
> const struct ad7380_chip_info *chip_info;
> struct spi_device *spi;
> struct regmap *regmap;
> unsigned int vref_mv;
> + unsigned int vcm_mv[2];
> /*
> * DMA (thus cache coherency maintenance) requires the
> * transfer buffers to live in their own cache lines.
> @@ -304,6 +333,11 @@ static int ad7380_read_raw(struct iio_dev *indio_dev,
> *val2 = chan->scan_type.realbits;
>
> return IIO_VAL_FRACTIONAL_LOG2;
> + case IIO_CHAN_INFO_OFFSET:
> + *val = st->vcm_mv[chan->channel] * (1 << chan->scan_type.realbits)
> + / st->vref_mv;
So this maths seems to be right to me, but it took me a while to figure it out.
Perhaps a comment would help along the lines of this is transforming
(raw * scale) + vcm_mv
to
(raw + vcm_mv / scale) * scale
as IIO ABI says offset is applied before scale.
> +
> + return IIO_VAL_INT;
> }
>
> return -EINVAL;
> @@ -350,7 +384,7 @@ static int ad7380_probe(struct spi_device *spi)
> struct iio_dev *indio_dev;
> struct ad7380_state *st;
> struct regulator *vref;
> - int ret;
> + int ret, i;
>
> indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));
> if (!indio_dev)
> @@ -394,6 +428,40 @@ static int ad7380_probe(struct spi_device *spi)
> st->vref_mv = AD7380_INTERNAL_REF_MV;
> }
>
> + if (st->chip_info->num_vcm_supplies > ARRAY_SIZE(st->vcm_mv))
> + return dev_err_probe(&spi->dev, -EINVAL,
> + "invalid number of VCM supplies\n");
> +
> + /*
> + * pseudo-differential chips have common mode supplies for the negative
> + * input pin.
> + */
> + for (i = 0; i < st->chip_info->num_vcm_supplies; i++) {
> + struct regulator *vcm;
> +
> + vcm = devm_regulator_get_optional(&spi->dev,
Why optional?
> + st->chip_info->vcm_supplies[i]);
> + if (IS_ERR(vcm))
This will fail if it's not there, so I'm guessing you are using this to avoid
getting to the regulator_get_voltage? If it's not present I'd rely on that
failing rather than the confusing handling here.
When the read of voltage wasn't in probe this would have resulted in a problem
much later than initial setup, now it is, we are just pushing it down a few lines.
Arguably we could have a devm_regulator_get_not_dummy()
that had same implementation to as get_optional() but whilst it's called that
I think it's confusing to use like this.
> + return dev_err_probe(&spi->dev, PTR_ERR(vcm),
> + "Failed to get %s regulator\n",
> + st->chip_info->vcm_supplies[i]);
> +
> + ret = regulator_enable(vcm);
> + if (ret)
> + return ret;
> +
> + ret = devm_add_action_or_reset(&spi->dev,
> + ad7380_regulator_disable, vcm);
> + if (ret)
> + return ret;
> +
> + ret = regulator_get_voltage(vcm);
I'd let this fail if we have a dummy regulator.
> + if (ret < 0)
> + return ret;
> +
> + st->vcm_mv[i] = ret / 1000;
> + }
> +
