Re: [PATCH v7 2/2] iio: adc: add MAX40080 current-sense amplifier driver

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 18 Aug 2026 17:29:28 +0300
Stefan Popa <stefan.popa@analog.com> wrote:

> The MAX40080 is a bidirectional current-sense amplifier with an
> integrated 12-bit ADC and an I2C/SMBus interface. It measures the
> voltage across an external shunt resistor and the input bus voltage,
> storing the results in an internal FIFO.
> 
> Add a direct-mode IIO driver exposing the current and voltage channels
> with raw, scale and hardware-gain attributes, a configurable
> oversampling (digital averaging) ratio, and PEC-protected register
> access. The current scale is derived from the shunt resistor value
> described in the device tree.
> 
> The driver operates in single-measurement mode: each raw read triggers
> an on-demand conversion via SMBus Quick Command and returns a matched
> current/voltage pair. This avoids the latency and complexity of the
> continuous FIFO mode while ensuring each read reflects the current
> state. The two selectable current-sense ranges are exposed through
> scale/scale_available.
> 
> Continuous FIFO buffering, threshold events and the alert interrupt are
> intentionally left out of this initial submission and may be added
> later.
https://sashiko.dev/#/patchset/20260818142928.8244-1-stefan.popa%40analog.com

The copy being optimized out is likely complier optimization so I think
sashiko is correct that you need READ_ONCE() (and probably the WRITE_ONCE()
as well)

> 
> Co-developed-by: Ciprian Hegbeli <ciprian.hegbeli@analog.com>
> Signed-off-by: Ciprian Hegbeli <ciprian.hegbeli@analog.com>
> Signed-off-by: Stefan Popa <stefan.popa@analog.com>
Otherwise, just trivial stuff from me.  Andy caught a lot more than me!

Given this seems to be coming to a point where it is ready to be applied
(hopefully v8) feel free to send a new version out in a day or two rather
than waiting a week.

Thanks

Jonathan

> diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
> index 7cc8f9a12f763..9245a337dd935 100644
> --- a/drivers/iio/adc/Makefile
> +++ b/drivers/iio/adc/Makefile
> @@ -166,3 +166,4 @@ obj-$(CONFIG_VIPERBOARD_ADC) += viperboard_adc.o
>  obj-$(CONFIG_XILINX_AMS) += xilinx-ams.o
>  xilinx-xadc-y := xilinx-xadc-core.o xilinx-xadc-events.o
>  obj-$(CONFIG_XILINX_XADC) += xilinx-xadc.o
> +obj-$(CONFIG_MAX40080) += max40080.o
> diff --git a/drivers/iio/adc/max40080.c b/drivers/iio/adc/max40080.c
> new file mode 100644
> index 0000000000000..4b397bcd145b2
> --- /dev/null
> +++ b/drivers/iio/adc/max40080.c

> +/*
> + * Configure the device from the cached state. The device powers up in standby
> + * with PEC enabled (CFG POR = 0x0060), so PEC is kept enabled throughout.
> + */
> +static int max40080_init(struct max40080_state *st)
> +{
> +	u16 fifo_cfg, cfg;
> +	int ret, filter;
> +
> +	filter = max40080_oversampling_to_filter(st->oversampling_ratio);
> +	if (filter < 0)
> +		return filter;
> +
> +	/*
> +	 * Put the device in standby before (re)configuring the FIFO: the FIFO
> +	 * configuration register can only be written while the device is not
> +	 * converting.
> +	 */
> +	cfg = FIELD_PREP(MAX40080_CFG_MODE_MSK, MAX40080_CFG_MODE_STDBY) |
> +	      FIELD_PREP(MAX40080_CFG_PEC_EN_MSK, 1);
> +

As below.

> +	ret = i2c_smbus_write_word_data(st->client, MAX40080_REG_CFG, cfg);
> +	if (ret)
> +		return ret;
> +
> +	/* Store a matched current+voltage pair per conversion. */
> +	fifo_cfg = FIELD_PREP(MAX40080_FIFO_CFG_STORE_IV_MSK, MAX40080_FIFO_CFG_STORE_IV);
> +

Where you have pairs like this of setting local and using it, drop the blank line.
We want those to be visually closely coupled.

> +	ret = i2c_smbus_write_word_data(st->client, MAX40080_REG_FIFO_CFG,
> +					fifo_cfg);
> +	if (ret)
> +		return ret;