linux-kernel - Re: [RFC PATCH v2] rtc: pcf2127: Add PPS capability through Seconds Interrupt

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Message-ID: <Zmks31shpsnoLQ3k@hoboy.vegasvil.org>
Date: Tue, 11 Jun 2024 22:06:39 -0700
From: Richard Cochran <richardcochran@...il.com>
To: Csókás, Bence <csokas.bence@...lan.hu>
Cc: linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Szentendrei, Tamás <szentendrei.tamas@...lan.hu>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Miroslav Lichvar <mlichvar@...hat.com>
Subject: Re: [RFC PATCH v2] rtc: pcf2127: Add PPS capability through Seconds
 Interrupt

(adding Miroslav onto CC)

On Tue, Jun 11, 2024 at 05:04:57PM +0200, Csókás, Bence wrote:

> PCF2127/29/31 is capable of generating an interrupt on every
> second (SI) or minute (MI) change. It signals this through
> the Minute/Second Flag (MSF) as well, which needs to be cleared.

This is a RFC, and my comment is that a PPS from an RTC is not useful
to the Linux kernel.

The kernel only uses the RTC to boot strap the wall clock to some
approximate phase.

After that, Linux either continues with a free running clock, or it
synchronizes to a global time source via NTP.  In the latter case,
Linux will write the NTP time back into the RTC.

So I can't see how the RTC's PPS provides any benefit.

Thanks,
Richard