Re: [PATCH v3 3/3] iio: adc: add driver for the MAX34417 Four-Channel High Dynamic Range Power Accumulator

[Neil Armstrong]

On 10/20/26 11:13, David Laight wrote:
> On Tue, 13 Oct 2026 16:07:13 +0200
> Neil Armstrong <neil.armstrong@xxxxxxxxxx> wrote:
>
> > The MAX34417 is a specialized current and voltage monitor used to
> > determine power consumption of portable systems. The driver support
> > getting the channels voltage, average power and accumulated average
> > power and energy over an I2C/SMBUS serial interface.
> >
> > The MAX34417 datasheet only specified on how to calculate the
> > accumulated average power, but with the Sample Per Second rate
> > we can easily get accumulated Energy in mJ.
> >
> > By default the IIO driver only supports single-shot Voltage
> > and Power sensing, but the accumulation can be enabled by
> > enabling the Energy IIO channel which then enables the
> > Continuous Accumulation Mode.
> >
> > The counter is common to all channels, so when reading a single
> > channel we will copy all accumulators to registers, so in order
> > to permit reading individual channels we must accumulate the
> > other channels in the driver when Continuous Accumulation Mode
> > is enabled.
> >
> > Signed-off-by: Neil Armstrong <neil.armstrong@xxxxxxxxxx>
> ...
> > +#define MAX34417_POWER_READ_LENGTH	8
> > +#define MAX34417_POWER_READ_OFFSET	1
> ...
> > +static int max34417_read_acc_power(struct max34417_data *max34417, unsigned int address,
> > +				   u64 *acc_power)
> > +{
> > +	u8 buf[MAX34417_POWER_READ_LENGTH];
> > +	int rc;
> > +
> > +	rc = regmap_noinc_read(max34417->regmap, address, &buf, sizeof(buf));
> > +	if (rc)
> > +		return rc;
> > +
> > +	/* Ignore byte0 */
> > +	*acc_power = get_unaligned_be56(&buf[MAX34417_POWER_READ_OFFSET]);
> > +
> > +	return 0;
> > +}
>
> I was thinking:
> 	struct { u64 pad:8; val:56 } buf;
> then using bswap64(buf.val) >> 8 on LE.
> But why not just:
> 	u64 buf;
> and be64toh(buf) & (BITULL(56) - 1)

Right, I mean all this could work but I would like to keep using something
simpler and get_unaligned_be56 matches all this.
I don't think the need for performance is enough to use complex ways to get
the value.

Thanks,
Neil

> David