linux-kernel - Re: [PATCH] clocksource: timer-tegra186: Enable WDT at probe

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Message-ID: <0afa0fbf2c19069e710b9c506fb66bec2f904e74.camel@nvidia.com>
Date: Thu, 3 Jul 2025 08:23:14 +0000
From: Kartik Rajput <kkartik@...dia.com>
To: "thierry.reding@...il.com" <thierry.reding@...il.com>
CC: "tglx@...utronix.de" <tglx@...utronix.de>, Jon Hunter
	<jonathanh@...dia.com>, "daniel.lezcano@...aro.org"
	<daniel.lezcano@...aro.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-tegra@...r.kernel.org"
	<linux-tegra@...r.kernel.org>
Subject: Re: [PATCH] clocksource: timer-tegra186: Enable WDT at probe

On Thu, 2025-07-03 at 08:55 +0200, Thierry Reding wrote:
> On Mon, Jun 30, 2025 at 04:31:35PM +0530, Kartik Rajput wrote:
> > Currently, if the system crashes or hangs during kernel boot before
> > userspace initializes and configures the watchdog timer, then the
> > watchdog won’t be able to recover the system as it’s not running.
> > This
> > becomes crucial during an over-the-air update, where if the newly
> > updated kernel crashes on boot, the watchdog is needed to reset the
> > device and boot into an alternative system partition. If the
> > watchdog
> > is disabled in such scenarios, it can lead to the system getting
> > bricked.
> > 
> > Enable the WDT during driver probe to allow recovery from any
> > crash/hang
> > seen during early kernel boot. Also, disable interrupts once
> > userspace
> > starts pinging the watchdog.
> > 
> > Signed-off-by: Kartik Rajput <kkartik@...dia.com>
> > ---
> >  drivers/clocksource/timer-tegra186.c | 42
> > ++++++++++++++++++++++++++++
> >  1 file changed, 42 insertions(+)
> 
> This seems dangerous to me. It means that if the operating system
> doesn't start some sort of watchdog service in userspace that pings
> the
> watchdog, the system will reboot 120 seconds after the watchdog
> probe.
> 

This is not the case. The driver keeps petting the watchdog with the
ISR until userspace takes over. So, the watchdog does not expires even
if userspace takes more time to load.

Thanks & Regards,
Kartik