Am 4. Juli 2026 18:17:07 MESZ schrieb Tom Rini <[email protected]>: >On Sat, Jul 04, 2026 at 05:21:25PM +0200, Carlo Caione wrote: >> >> >> > On 4 Jul 2026, at 16:32, Tom Rini <[email protected]> wrote: >> > >> > 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 <[email protected]> >> > >> > 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. >> >> >> Fair enough. >> >> For the record, the failure that motivated this: a pristine Ubuntu 26.04 >> arm64 image on a MediaTek Genio 700 EVK dies silently about 60 seconds after >> ExitBootServices(), 100% reproducible, at a wall-clock dependent point. The >> generic kernel ships the watchdog driver as a module, so nothing services >> the watchdog in time, and nothing tells the OS that it is running. From the >> user's side this is indistinguishable from broken firmware. >> >> In the meantime, is the accepted pattern hooking up a wdt_stop_all() in the >> EFI path via board_quiesce_devices()? That keeps the watchdog armed for the >> whole firmware lifetime and makes the handoff behaviour the board >> maintainer's call. > >No, Ubuntu needs to fix their kernel image to have the watchdog >available early. I hate to be difficult on this, but it's been a known >issue for years at this point that the spec needs to be updated. The >workaround here is for the watchdog to not be started until the OS is >ready to maintain it. >
Best open a Launchpad bug explaining why this watchdog driver needs to be built in and not a module. Best regards Heinrich
