Watchdog NO_REBOOT flag fail

hariprasath — Thu, 25 Jun 2026 07:50:13 GMT

I am investigating hardware watchdog support on an Intel Elkhart Lake platform (J6412/J6426 based board).

The kernel is built with Intel TCO watchdog support:

CONFIG_ITCO_WDT=y

CONFIG_ITCO_VENDOR_SUPPORT=y

CONFIG_WATCHDOG=y

During boot, the kernel detects the watchdog hardware and the iTCO driver initializes, but reports:

iTCO_vendor_support: vendor-support=0

iTCO_wdt iTCO_wdt: unable to reset NO_REBOOT flag, device disabled by hardware/BIOS

As a result /sys/class/watchdog/ is empty and no /dev/watchdog device is created.

However, when I enable the watchdog in BIOS and configure a 2-minute timeout, the system reliably reboots after approximately 2 minutes if left unattended. This suggests that the watchdog hardware is present and functional, but appears to remain under firmware ownership.

Even Though I enabled the BIOS Watchdog there is node created under /dev to feed the watchdog.

My understanding is:

* The iTCO watchdog hardware is detected by Linux.

* The kernel driver is present and attempts initialization.

* Firmware/BIOS prevents Linux from clearing the NO_REBOOT flag and taking ownership.

* Therefore the watchdog is not exposed to Linux user space.

* The watchdog continues to operate under BIOS/firmware control.

Is this interpretation correct?

Also, on Intel Elkhart Lake platforms, is there a known BIOS update, ACPI interface, or platform configuration required to allow Linux to take ownership of the TCO watchdog and create `/dev/watchdog`?

Re: Watchdog NO_REBOOT flag fail

Jaime_Lizarme — Mon, 29 Jun 2026 14:09:34 GMT

Hi @hariprasath

Thank you for contacting the Intel Embedded Community. Even though The Elkhart Lake processor supports some Linux distributions (i.e Ubuntu), its technical support is given by each Linux provider, so I will try to answer your questions; however, we recommend contacting your Linux provider for this implementation. Wi that being said se below the answer to your question:

"is there a known BIOS update, ACPI interface, or platform configuration required to allow Linux to take ownership of the TCO watchdog and create `/dev/watchdog`?"

A/ Yes, on Intel Elkhart Lake platforms, a known BIOS/firmware configuration is required to allow Linux to take ownership of the TCO watchdog and create /dev/watchdog. This includes:

BIOS clearing the SECOND_TO_STS and TIMEOUT bits before OS handoff.
BIOS setting the No Reboot bit to prevent unwanted resets.
Leaving the watchdog timer reset responsibility to the OS driver.
Proper initialization of TCO I/O space and enabling watchdog timer features.

If these steps are not correctly implemented in the BIOS/firmware, Linux may not be able to take ownership of the TCO watchdog, and /dev/watchdog may not be created.

Best regards,

Jaime L.

Thema "Re: Watchdog NO_REBOOT flag fail" in Embedded Intel® Core™ Processors

Watchdog NO_REBOOT flag fail

Re: Watchdog NO_REBOOT flag fail