Re: [PATCH] iio: imu: inv_icm42600: fix timestamping by limiting FIFO reading

[Andy Shevchenko]

On Tue, Jun 23, 2026 at 06:44:22PM +0200, Jean-Baptiste Maneyrol via B4 Relay wrote:

> Timestamps are made by measuring the chip clock using the watermark
> interrupts. If we read more than watermark samples as done today, we
> are reducing the period between interrupts and distort the period
> measurement. Fix that by reading only watermark samples in the
> interrupt case.
> 
> Better watermark computation using gcd and store watermark value for
> FIFO reading.

...

> +		/* use the shortest period and the gcd of the latencies */
> +		period = min(period_gyro, period_accel);
> +		latency = gcd(latency_gyro, latency_accel);

If gyro is 5 and accel is 7 the gcd() will give 1. I don't think it's what you
want.

Did you think of lcm()?

...

> +	/* update effective watemarks */
> +	st->fifo.watermark.value = max(latency / period, 1);
> +	if (wm_gyro)
> +		st->fifo.watermark.eff_gyro = max(latency / period_gyro, 1);
> +	if (wm_accel)
> +		st->fifo.watermark.eff_accel = max(latency / period_accel, 1);

In my example this ends up with 1 in both cases.

-- 
With Best Regards,
Andy Shevchenko