ARM: mach-at91: how to stop U-Boot/SPL from disabling the watchdog timer on SAMAD3 Xplained

Quentin Schulz quentin.schulz at
Thu Dec 9 17:43:03 CET 2021

Hi Michael,

On Thu, Dec 09, 2021 at 05:32:51PM +0100, Michael Opdenacker wrote:
> Greetings,
> Documenting the issue and a workaround here in case other people
> encounter it, but if you have tips for fixing the issue in U-Boot, I'm
> interested of course!
> I noticed that the SAMA5D3 Xplained board didn't have the watchdog timer
> enabled in the Linux DTS.
> I submitted a patch to fix this: 
> However, applying this patch isn't sufficient to make the watchdog
> available on Linux:
> at91_wdt fffffe40.watchdog: watchdog is disabled
> at91_wdt: probe of fffffe40.watchdog failed with error -22
> As explained on
> ,
> this happens because the bootloader or bootstrap code already disables
> the watchdog. The trouble is, unlike on SAMA5D2 and SAMAD4 (if I
> understood correctly),"The Watchdog Timer Mode Register can be only
> written to once".
> However, I haven't managed to disable this behavior in U-Boot (including
> the SPL). I have no watchdog related option turned on anywhere, and by
> adding puts() messages in the code, I believe that the wdt_stop()
> function doesn't get called either. Maybe the corresponding watchdog
> register is written to by the code initializing the SoC, but I couldn't
> find where.

>From a quick look at the code, you need to enable CONFIG_WDT_AT91 and
the watchdog won't be disabled anymore by the SPL.



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