Re: [PATCH] efi_loader: stop watchdog devices in ExitBootServices()

[Tom Rini <trini@konsulko.com>]

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On Sat, Jul 04, 2026 at 03:52:29PM +0200, Carlo Caione wrote:

> U-Boot can autonomously start a hardware watchdog
> (CONFIG_WATCHDOG_AUTOSTART, default y) and service it from its main
> loop, but the EFI boot path never stops it: efi_exit_boot_services()
> tears the devices down without calling wdt_stop_all(), and a watchdog
> driver without a .remove hook leaves the hardware ticking across the
> firmware-to-OS handoff.
> 
> An EFI-booted OS that does not take over the SoC watchdog within the
> remaining timeout is reset mid-boot at a wall-clock-dependent point.
> 
> The UEFI specification (v2.11, section 7.5 "Miscellaneous Boot
> Services", EFI_BOOT_SERVICES.SetWatchdogTimer()) is explicit about the
> one watchdog it allows across the handoff:
> 
>   "The watchdog timer is only used during boot services. On
>    successful completion of EFI_BOOT_SERVICES.ExitBootServices() the
>    watchdog timer is disabled."
> 
> U-Boot's UEFI watchdog (an EFI timer event) complies by construction. A
> platform watchdog silently surviving the handoff defeats the purpose of
> that rule: the OS has no generic way to know it is running, let alone to
> service it.
> 
> Stop all watchdog devices in efi_exit_boot_services(), before the device
> teardown.
> 
> Signed-off-by: Carlo Caione <ccaione@baylibre.com>

NAK. We have had this come up before, and in short, the UEFI
specification needs to be fixed here, as generally speaking a watchdog
should never be stopped, as that leaves a gap where the system can hang
and thus defeat the point of having enabled a watchdog.

-- 
Tom

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