On Sat, Jul 04, 2026 at 06:59:08PM +0200, Heinrich Schuchardt wrote: > 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.
I'll leave that to Carlos, and I would suggest digging out the mailing list threads from a year or two (or three?) ago when this had come up before, and the problem was explained and it was spelled out that U-Boot will not be spec compliant here, and I thought someone even volunteered to take this to the spec to get updated. -- Tom
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