Re: [PATCH v6 5/6] iio: pressure: dps310: add hardware FIFO support

[Rupesh Majhi]

On Thu, 10 Sep 2026 03:36:36 +0100
Jonathan Cameron <jic23@xxxxxxxxxx> wrote:

> Maybe we just set the minimum allowed watermark to something that
> in practice always has a temperature (or almost does)? It's kind
> of true that a watermark below that doesn't work because we end
> up dropping data.

Two temperature entries are prs_rate / tmp_rate pressure entries apart, so
a batch needs one more than that before it is sure of catching one. The
FIFO holds 32, so there is no such watermark once the ratio reaches 32.
That is six of the 64 rate pairs, and one of them is pressure 32 Hz with
temperature 1 Hz, the case that found this, which would want 33.

So I will hold them locally instead, which is what you asked for first. The
drain timer runs at half the fill time, so nothing overflows while the
driver waits, and the hold lasts only until the first temperature of the
session, bounded by the rate ratio at 128 entries. The first push still
waits for that temperature, but only once per enable, and no pressure entry
is dropped. I will re-run the zero output regression against it.

> Validity flag in the data we push to userspace?  That never works because
> we don't have a universal encoding for one.

I meant driver state, not a channel. Moot now.

Rupesh