linux-kernel - battery switch-over detection on pcf2127

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Date:   Tue, 5 May 2020 21:54:47 +0200
From:   Rasmus Villemoes <rasmus.villemoes@...vas.dk>
To:     Bruno Thomsen <bruno.thomsen@...il.com>
Cc:     Per Nørgaard Christensen 
        <per.christensen@...vas.dk>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: battery switch-over detection on pcf2127

Hi Bruno

I just noticed your "rtc: pcf2127: add tamper detection support"
(03623b4b04) from 5.4. Unfortunately, clearing the BTSE bit breaks a use
case of ours:

We rely on the battery switch-over detection to distinguish a powerfail
during boot from a PORESET by the external watchdog (in the latter case,
the RTC is still powered throughout, meaning there is no battery
switch-over event). OTOH, we do not use the tamper detection - in fact,
the TS signal is unconnected on our board.

We're currently still on 4.19, but we will eventually upgrade to a
kernel containing the above commit. So I was wondering if we could
figure out a way that would work for both of us - either some CONFIG
knob, or perhaps something in the device-tree. Any ideas?

Rasmus