[PATCH v3 0/6] Improved sysreset/watchdog uclass integration

Heinrich Schuchardt heinrich.schuchardt at canonical.com
Tue Nov 9 15:34:43 CET 2021

On 11/9/21 15:26, Andre Przywara wrote:
> On Tue, 9 Nov 2021 08:50:37 -0500
> Tom Rini <trini at konsulko.com> wrote:
> Hi,
>> On Tue, Nov 09, 2021 at 09:00:05AM +0100, Heinrich Schuchardt wrote:
>> [snip]
> thanks for that ;-)
>>>> I am still puzzled about this, if I read the UEFI spec correctly, the
>>>> 5 minutes watchdog timer is for EFI applications using boot services?
>>>> So grub, for instance. But the description of ExitBootServices tells me
>>>> that the: "boot services watchdog timer is disabled"?
>>>> So it should not affect Linux booting (after the EFI stub is done)?
>>> Currently we only disable the software watchdog (efi_tpl = TPL_HIGH_LEVEL;)
>>> We should call wdt_stop_all() too. I will create a patch for that.
>> Lets use this as a chance to bring up the issue with the relevant part
>> of the UEFI forum.  Turning off a running watchdog is a bad idea in
>> places where Arm is pushing SystemReady IR (and I would argue other
>> specs as well, but..).
> I think architecturally you have no other chance than turning it
> off at boot. You do not know what your payload is (Linux? BSD? Xen?
> homebrew kernel?), which watchdog it is using, or if it's using one at all
> (no driver). Also for instance sunxi has typically two watchdogs, which
> one is it that needs petting?
> And even an opt-in from the EFI application (the kernel's EFI stub) sounds
> hard, as the Linux EFI stub for instance has no insight into the watchdog
> configuration, so can't say whether we have a driver or whether that
> would work (because of a missing firmware table).
> But it indeed sounds like a rather generic problem, and there might indeed
> be a solution generic enough for UEFI.
> Do you have anything in mind?
> Cheers,
> Andre

Hello Grant, hello Ozog,

according to the UEFI spec the watchdog should be shut down in 
ExitBootServices(). In an IoT scenario this may not always make sense. 
E.g. if A/B boot fails you want to reset the board to its previous state.

Is this something to discuss in the EBBR context?
Is there any requirement in SystemReady ES?

Best regards


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