[PATCH 0/3] watchdog: honour hw_margin_ms property

[Stefan Roese]

On 02.06.20 15:29, Rasmus Villemoes wrote:
> On 16/03/2020 16.52, Rasmus Villemoes wrote:
>> On 14/03/2020 13.04, Stefan Roese wrote:
>>> On 13.03.20 17:04, Rasmus Villemoes wrote:
>>
>>>> That at least solves half my problems and
>>>> might be useful to others as well. Then I'll have to figure out the
>>>> time-stands-still problem in some other way.
>>>
>>> If its too hard to enable interrupts in SPL for you or to provide some
>>> other means of a working get_timer() API, then we needto find another
>>> solution. You started with this weak function, which of course works.
>>> What other options are there? Adding a callback mechanism to register
>>> platform specific callback functions? Even though this might get a
>>> little bit too complicated.
>>
>> Now that I dig a bit more into this, I seem to remember that we actually
>> also had problems in U-Boot proper when loading a compressed kernel, so
>> for now we're using an uncompressed kernel in our FIT images. I will
>> have to re-investigate, but it now occurs to me that it might be due to
>> the fact that interrupts get disabled during bootm (which makes sense,
>> the same reason I stated previously of interrupt vectors about to be
>> overwritten), so even in U-Boot proper, time as measured by get_timer()
>> ceases to pass after that point, so all the WATCHDOG_RESET() calls from
>> the inflate code effectively get ignored.
>>
>> So it may be necessary to have some wdt_ratelimit_disable() hook that
>> can be called from bootm_disable_interrupts() and e.g. some
>> board-specific SPL code. I'll do some experiments and figure out if I do
>> indeed need such a hook.
> 
> OK, I have now had time to do some more experiments. I have enabled the
> timer tick in SPL, so get_timer() now "normally" works. Together with
> the .dts based read of the hardware margin, that makes the watchdog
> handling mostly work.
> 
> But, as I suspected, I do have a problem when loading a compressed
> kernel image - what I write above "so even in U-Boot proper, time as
> measured by get_timer() ceases to pass after that point, so all the
> WATCHDOG_RESET() calls from the inflate code effectively get ignored."
> is indeed the case.
> 
> So, what's the best way to proceed? Should there be a hook disabling the
>   rate-limiting logic that bootm_disable_interrupts() can call? Or must
> get_timer() always return a sensible result even with interrupts disabled?

Wouldn't it make sense to move the bootm_disable_interrupts() call to
after loading and uncompressing the OS image? To right before jumping
to the OS?

Thanks,
Stefan