Re: [PATCH v3 7/8] iio: adc: ti-ads112c14: implement gain on internal short SYS_MON channel

[Jonathan Cameron <jic23@kernel.org>]

On Fri, 10 Jul 2026 17:50:40 -0500
"David Lechner (TI)" <dlechner@baylibre.com> wrote:

> Implement support for the programmable gain amplifier on the internal
> short SYS_MON channel. This channel is used for calibration, so it is
> useful to be able to set the PGA to the same gain as the external
> channels. The gain setting is implemented via the `_scale` attribute.
> 
> In the future, we may want to support different reference voltages for
> this channel, so the scale_available table is populated during probe
> rather than being a static table.
> 
> Signed-off-by: David Lechner (TI) <dlechner@baylibre.com>
> ---
> v3 changes:
> * Use IIO_VAL_DECIMAL64_PICO for scale.

Sashiko (I think rightly) raised endian concerns on the read_avail
side of things.  It think you need to do the decompose to fill that
that rather than relying on placement of bytes in the 64 bit int.


Jonathan

> ---
>  drivers/iio/adc/ti-ads112c14.c | 128 ++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 125 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/adc/ti-ads112c14.c b/drivers/iio/adc/ti-ads112c14.c
> index 4d2e7d37be82..2ce4411a0d86 100644
> --- a/drivers/iio/adc/ti-ads112c14.c
> +++ b/drivers/iio/adc/ti-ads112c14.c

>  
> +static int ads112c14_read_avail(struct iio_dev *indio_dev,
> +				const struct iio_chan_spec *chan, const int **vals,
> +				int *type, int *length, long mask)
> +{
> +	struct ads112c14_data *data = iio_priv(indio_dev);
> +
> +	if (chan->channel == ADS112C14_SYS_MON_CHANNEL_SHORT) {
> +		*vals = (const int *)data->sys_mon_chan_short_scale_available;

Sashiko is mean about this and it may have a point.. Definitely needs
a comment as you are forcing a u64 to be interpreted as an array of ints and
on big endian systems the top and bottom half will get swapped.

> +		*length = 2 * ARRAY_SIZE(data->sys_mon_chan_short_scale_available);
> +		*type = IIO_VAL_DECIMAL64_PICO;
> +		return IIO_AVAIL_LIST;
> +	}
> +
> +	return -EINVAL;
> +}
> +

>  
> +static void ads112c14_populate_scale_available(s64 *scale_avail, u32 full_scale,
> +					       u32 fsr_bits)
> +{
> +	for (u32 i = 0; i < ARRAY_SIZE(ads112c14_pga_gains_x10); i++) {
> +		u64 gain_x10 = ads112c14_pga_gains_x10[i];
> +
> +		scale_avail[i] = div64_u64((u64)PICO * 10U * full_scale,
> +					   gain_x10 * BIT(fsr_bits));

I think this needs to happen into a local variable that is then decomposed
into two int elements of scale_avail[]. I.e. type of that needs to change.

> +	}
> +}