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

[David Laight <david.laight.linux@gmail.com>]

On Tue, 13 Oct 2026 16:07:13 +0200
Neil Armstrong <neil.armstrong@linaro.org> 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@linaro.org>
...
> +#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)

David