Re: [PATCH v4 2/4] pps: Drop the !NO_HZ_COMMON dependency from NTP_PPS

[Rodolfo Giometti]

Hi David,

On 30/09/2026 20:24, David Woodhouse wrote:
> On Wed, 2026-09-30 at 15:05 +0100, David Woodhouse wrote:
> > [...] But
> > I don't think we're ever going to be allowed to do it that way in
> > entry.S but the *hardware-captured* stamps will want the same handling,
> > so I wanted to prototype it anyway.

Hardware-captured stamps are something I'd really like to see in the PPS
subsystem. When you get there, I think it should be its own series,
discussed together with the raw counter export you mentioned on the
28th, since both change what a PPS driver hands to the core and what
userspace gets back. As I said for the export, I'd prefer to agree on
the interface first.

> We don't actually do *any* filtering. Even pps_phase_filter_get() is
> just using the first sample, with a comment:
>
> 	/* TODO: test various filters */
>
> Looking closer at the actual captures, even Mills's median-of-three
> wouldn't save us here when two of the three pulses are outliers. We'd
> want an ongoing frequency estimation.
>
> But that's definitely a problem for another day.

Agreed, but I'm interested in it too. Your setup, with the per-pulse
captures, looks like a good way to evaluate a filter, so if you or
anyone else picks it up, please Cc me and I'll be glad to review it.

Ciao,

Rodolfo