linux-kernel - Re: [PATCH v2 2/2] rtc: pcf2127: Run a OTP refresh if not done before

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20210114111157.GC3654@piout.net>
Date:   Thu, 14 Jan 2021 12:11:57 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Philipp Rosenberger <p.rosenberger@...bus.com>
Cc:     dan.carpenter@...cle.com, u.kleine-koenig@...gutronix.de,
        biwen.li@....com, lvb@...hos.com, bruno.thomsen@...il.com,
        l.sanfilippo@...bus.com, Alessandro Zummo <a.zummo@...ertech.it>,
        linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] rtc: pcf2127: Run a OTP refresh if not done before

On 14/01/2021 11:30:37+0100, Philipp Rosenberger wrote:
> > > +	ret = regmap_set_bits(pcf2127->regmap, PCF2127_REG_CLKOUT,
> > > +			      PCF2127_BIT_CLKOUT_OTPR);
> > > +	if (ret < 0) {
> > > +		dev_err(dev, "%s: OTP refresh (clkout_ctrl) failed.\n", __func__);
> > 
> > Please drop this error message.
> 
> If I return from the probe with an error, shouldn't there be an error
> message? Or should I ignore the problem at all and don't return from the
> probe?

You can return from probe without an error message.

> 
> > 
> > > +		return ret;
> > > +	}
> > > +	msleep(100);
> > 
> > Maybe this should be done just before setting the time. Or if you want
> > to keep it in probe, then you could optimise by not waiting but ensuring
> > the time between pcf2127_probe and the first pcf2127_rtc_set_time is
> > more than 100ms.
> > 
> 
> Doing it just before setting the time might be not the best way. The
> watchdog might be used before the OTPR is done.
> 
> From the PCF2129 manual:
> | The OTP refresh (see Section 8.3.2 on page 13) should ideally be
> | executed as the first instruction after start-up and also after a
> | reset due to an oscillator stop.
> 
> As I see it this should be done before setting up the watchdog as well. So
> sleeping if the OTPR wasn't done before might be the most viable solution.
> So I would check the OTPR and only if the OTPR is not set starting an OTPR
> and then sleep 100ms.
> 

Indeed, the remaining question is whether you should test OTPR or OSF.
OSF states: "oscillator has stopped and chip reset has occurred since
flag was last cleared" if OTPR is always 0 when OSF is 1, then OTPR is
probably enough.


-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com