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

[Grant Likely]

On 09/11/2021 14:34, Heinrich Schuchardt wrote:
> 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?

There is no requirement in ES as far as I'm aware. Yes, it makes sense
to discuss this w.r.t the EBBR spec. I agree that the watchdog should
not be turned off at EBS() time for most IR class platforms.

g.

>
> Best regards
>
> Heinrich

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