[PATCH v2] efi: stop hw watchdog during EBS

[Heinrich Schuchardt]

On 1/20/26 10:33, Mark Kettenis wrote:
>> From: Casey Connolly <casey.connolly at linaro.org>
>> Date: Mon, 19 Jan 2026 22:09:25 +0100
>>
>> Hardware watchdogs don't currently get stopped as part of
>> ExitBootServices, this can result in resets during boot if the OS
>> doesn't have a driver for the watchdog, or if the driver isn't loaded
>> in time.
>>
>> As with the EFI watchdog, stop any hardware watchdogs as well.
> 
> This has been discussed before and rejected on the grounds that this
> defeats the purpose of the watchdog.  I think there was some consensus
> that an OS that doesn't have a driver for the watchdog or doesn't load
> it in time is broken.  Some folks also pointed out that on some
> platforms it isn't possible to disable the watchdog.
> 
> Ultimately, I think EFI needs an API to control the hardware watchdog,
> such that an OS doesn't need a driver.

The hardware watchdog interrupting an OS if it is hanging is intended 
behavior. It is required for recovering from a failed capsule update.

Some watchdog timers have a maximum timeout that is too short for 
booting (e.g. 16s on some Sunxi boards). To avoid resets these options 
are available:

* Set CONFIG_WATCHDOG_AUTOSTART=n.
* Use device-tree property u-boot,noautostart.
* Use the `wdt stop` command in PREBOOT.

Best regards

Heinrich

> 
>> Signed-off-by: Casey Connolly <casey.connolly at linaro.org>
>> ---
>> Changes in v2:
>> * Fix compilation when CONFIG_WATCHDOG is disabled.
>>
>> ---
>>   lib/efi_loader/efi_boottime.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
>> index ddc935d22409..c34616db578a 100644
>> --- a/lib/efi_loader/efi_boottime.c
>> +++ b/lib/efi_loader/efi_boottime.c
>> @@ -21,8 +21,9 @@
>>   #include <time.h>
>>   #include <u-boot/crc.h>
>>   #include <usb.h>
>>   #include <watchdog.h>
>> +#include <wdt.h>
>>   #include <asm/global_data.h>
>>   #include <linux/libfdt_env.h>
>>   
>>   DECLARE_GLOBAL_DATA_PTR;
>> @@ -2263,8 +2264,10 @@ static efi_status_t EFIAPI efi_exit_boot_services(efi_handle_t image_handle,
>>   	efi_update_table_header_crc32(&systab.hdr);
>>   
>>   	/* Give the payload some time to boot */
>>   	efi_set_watchdog(0);
>> +	if (CONFIG_IS_ENABLED(WDT))
>> +		wdt_stop_all();
>>   	schedule();
>>   out:
>>   	if (IS_ENABLED(CONFIG_EFI_TCG2_PROTOCOL)) {
>>   		if (ret != EFI_SUCCESS)
>> -- 
>> 2.52.0
>>
>>