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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 >>>> --- >>>> 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. >> >> >> I don't believe that will happen with this change. The kernel will continue >> to pet the watchdog until userspace takes over with this change. At least >> that is my understanding. > > Ah yes... I skipped over that IRQ handling bit. However, I think this > still violates the assumptions because the driver will keep petting the > watchdog no matter what, which means that we now have no way of forcing > a reset of the system when userspace hangs. As long as just a tiny part > of the kernel keeps running, the watchdog would keep getting petted and > prevent it from resetting the system. > > Using a second watchdog still seems like a more robust alternative. Or > maybe we can find a way to remove the kernel petting once userspace > starts the watchdog. Once userspace calls the "->ping" callback then, 'enable_irq' is set to false and when 'tegra186_wdt_enable()' is called this will disable the IRQ so that the kernel no longer pets the watchdog. So this should disable kernel petting once userspace is up and running. Cheers! Jon -- nvpublic