linux-kernel - RE: [PATCH v3 2/4] watchdog: da9062: reset board on watchdog timeout

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Date:   Thu, 2 Dec 2021 12:12:03 +0000
From:   Adam Thomson <Adam.Thomson.Opensource@...semi.com>
To:     Andrej Picej <andrej.picej@...ik.com>,
        Christoph Niedermaier <cniedermaier@...electronics.com>,
        Support Opensource <Support.Opensource@...semi.com>,
        "linux@...ck-us.net" <linux@...ck-us.net>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>
CC:     "wim@...ux-watchdog.org" <wim@...ux-watchdog.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux-imx@....com" <linux-imx@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH v3 2/4] watchdog: da9062: reset board on watchdog timeout

On 02 December 2021 07:43, Andrej Picej wrote:

> > I have a question how to correctly restart the system after
> > watchdog timeout.
> > If I understand it correct after watchdog timeout the system
> > restarts only if WATCHDOG_SD (Bit 3) in register CONFIG_I is
> > set.
> > What is the difference if WATCHDOG_SD isn't set, but WAKE_UP
> > (Bit 2) in register CONTROL_F is set? From outside on my
> > system I observe the same behavior. After watchdog timeout
> > my system restarts. So where are the differences?
> > It would be nice if you could answer this question, as you
> > certainly know this chip very well.
> 
> To be honest I don't really know the chip that well, I'm just trying to
> add this feature and hopefully help others if they run into the same
> problem. I think @Adam will be more helpful here.
> 
> But from quick look at da9062 datasheet, mainly chapter "8.8 Power
> Modes" I see next main differences:
> - setting WATCHDOG_SD enables SHUTDOWN sequence when the watchdog
> timeout is triggered. This puts the chip (da9062) in RESET mode.
> Taken from DA9062 datasheet:
> > In RESET mode, the internal supplies, and LDO1 (if configured as an always-on
> supply) are enabled.
> > All other DA9062 supplies are disabled.
> > DA9062 is in RESET mode whenever a complete application shutdown is
> required
> > The DA9062’s register configuration will be re-loaded from OTP when leaving
> the RESET mode
> 
> - if you set the WAKE_UP bit than the chip enters POWERDOWN mode on
> watchdog timeout. I understand the POWERDOWN mode as a not that "deep"
> mode as a RESET mode Device will go from RESET mode to POWERDOWN mode in
> the sequence of powering-up.
> 
> The above explanation is just my understanding after quick look, @Adam
> please correct me if I'm talking nonsense.
> 
> Please have a look at the DA9062 datasheet for more information. Sorry,
> that I can't be more helpful here.

Yes, POWERDOWN doesn't go to RESET and thus doesn't re-read OTP, so some
settings will persist. Also, depending on the state of NRES_MODE, the nRESET pin
state may or may not be modified to reset the attached processor. The behaviour
of POWERDOWN and which regulators are disabled is down to the OTP configuration
of the device.

For transition to POWERDOWN, if the WAKE_UP bit is set then the device will
immediately transition back out of POWERDOWN to ACTIVE and the WAKE_UP bit will
be cleared after a time.