u-boot leaves watchdog enabled by default

[Tom Rini]

On Mon, Sep 21, 2020 at 11:01:37AM +0200, Stefan Roese wrote:
> Hi Michael,
> Hi Chris,
> 
> On 15.09.20 12:44, Chris Packham wrote:
> > 
> > 
> > On Tue, 15 Sep 2020, 7:54 PM Michael Walle, <michael at walle.cc> wrote:
> > 
> >     Am 2020-09-15 09:44, schrieb Rayagonda Kokatanur:
> >      > On Tue, Sep 15, 2020 at 12:56 PM Michael Walle <michael at walle.cc>
> >      > wrote:
> >      >>
> >      >> Hi Stefan,
> >      >>
> >      >> it appears that since commit 06985289d45 ("watchdog: Implement
> >     generic
> >      >> watchdog_reset() version") - by default - the first watchdog is
> >      >> started
> >      >> unconditionally if CONFIG_WDT is set but never stopped before
> >     booting
> >      >> the operating system.
> >      >>
> >      >> Shouldn't it also be stopped uncondionally? What's worse is that on
> >      >> one
> >      >> board/arch the watchdog is stopped in arch_preboot_os() which is
> >     never
> >      >> called in the bootefi case. So even if I'd do a workaround and
> >     stop it
> >      >> manually in my board code, I couldn't do that consistently for
> >      >> bootm/bootefi.
> >      >>
> >      >> Or am I missing something here?
> >      >
> >      > Define CONFIG_WATCHDOG.
> >      > This takes care of resetting wdt.
> > 
> >     Yes as along as you're inside the bootloader, but when u-boot hands
> >     control over the OS the watchdog is not serviced anymore; which wouldn't
> >     be a problem per se, but it is enabled unconditionally by u-boot.
> > 
> > 
> > Just to add some data. At $dayjob we use this behaviour as a failsafe to
> > make sure our userspace gets to a point where it is servicing the
> > watchdog.
> 
> Yes, this is exactly how this is supposed to work AFAIK.
> 
> Michael, are you sure that the watchdog was disabled in U-Boot when
> booting into the OS before this patch?
> 
> > That said having a leave-wdt-running environment variable would work for
> > our use case.
> 
> I would rather use it the other way around. Something like "wdt-stop-
> pre-os" to optionally stop the WDT before booting into the OS.
> 
> Remark:
> IMHO, if you don't use the WDT in the OS, it does not make much sense
> to enable the WDT in U-Boot.

Yes, we need to be very careful about making it so that a watchdog is
disabled and not re-enabled before moving on for a whole bunch of
reasons.  And the best option would be to just disable the watchdog if
it won't be used while the device is running the OS.

-- 
Tom
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