linux-kernel - RE: [PATCH 2/2] rtc: pcf2127: add battery-low INTn generation

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Date:   Wed, 3 Apr 2019 16:09:14 +0000
From:   Flavio Suligoi <f.suligoi@...m.it>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
CC:     Alessandro Zummo <a.zummo@...ertech.it>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "linux-rtc@...r.kernel.org" <linux-rtc@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/2] rtc: pcf2127: add battery-low INTn generation

Hi,

> On 03/04/2019 15:49:03+0000, Flavio Suligoi wrote:
> > > Then, you should probably not enable BLIE because this will cause
> issues
> > > with the alarm functionnality.. It is certainly enough to use
> > > RTC_VL_READ periodically.
> >
> > We use the nINT signaling solution because of this pin, in addition
> > to be used by the CPU, can be also connected to an external connector,
> > available for the final user.
> > Anyway, even if the BLIE is set, the sw low voltage alarm works,
> > with the message (displayed about every 12 minutes):
> >
> 
> I agree the DT property makes sense when the nINT pin is not connected
> to the CPU. But if it is, then you have an issue that nINT will be
> pulled low until the user changes the battery, meaning that you will
> not get any alarm interrupt anymore, possibly leading to a system that
> is not waking up anymore.

Ah, ok, thanks for the info. 
I know this, but in our specific case, this is not a problem,
since we don't use the nINT for other purposes, but only for
a battery low indicator. On the contrary, in our case, it's better
that the alarm signal remains low until the battery is changed.

Anyway, I can specify this collateral effect in a specific file for the
Pcf2127 in the DT bindings Documentation. What do you think?


Flavio Suligoi