[PATCH v3] watchdog: sbsa_gwdt: add early_enable module parameter

[Guenter Roeck]

On Thu, Aug 13, 2026 at 12:12:18PM +0800, Zexin Wang wrote:
> On SBSA platforms using standard UEFI firmware (such as EDK II), the
> watchdog timer is often enabled during early boot stages but explicitly
> disabled by the firmware before handing over control to the OS (e.g.,
> during ExitBootServices). This is done to prevent unintended resets
> while the OS is loading, assuming the OS watchdog driver will take over.
> 
> However, this leaves a protection gap. If the system hangs between the
> firmware handover and the userspace watchdog daemon startup, the hardware
> watchdog will not fire to recover the system. For safety-critical systems
> that require continuous hardware watchdog protection from the earliest
> possible moment, this gap is problematic.
> 
> Add an 'early_enable' module parameter to allow the kernel driver to
> re-enable the watchdog immediately during probe if it was left disabled
> by the firmware. By setting the WDOG_HW_RUNNING status bit, the watchdog
> core is instructed that the hardware is active. As a result, the core's
> pre-userspace handler (controlled by 'handle_boot_enabled') will
> automatically issue periodic keepalives until userspace opens the device.
> 
> This bridges the protection gap seamlessly without requiring firmware
> modifications and without risking unintended resets during kernel boot.
> 
> The parameter defaults to false to preserve the traditional behavior.
> 
> Signed-off-by: Zexin Wang <ot_zexin.wang at mediatek.com>

You might want to wait a few minutes before sending new versions
of a patch.

> ---
> Changes in v3:
> - Fix indentation of `early_enable` in watchdog-parameters.rst to ensure
>   it renders as a separate parameter rather than part of `nowayout`'s
>   description.
> 
> Changes in v2:
> - Rename `force_enable` to `early_enable` as suggested by Guenter.
> - Update commit message to explain the UEFI handover gap motivation.
> - Add documentation for the new parameter.
> 
>  .../watchdog/watchdog-parameters.rst          |  2 ++
>  drivers/watchdog/sbsa_gwdt.c                  | 23 +++++++++++++++++--
>  2 files changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/watchdog/watchdog-parameters.rst b/Documentation/watchdog/watchdog-parameters.rst
> index 502cb6adbeda..348229ffcb43 100644
> --- a/Documentation/watchdog/watchdog-parameters.rst
> +++ b/Documentation/watchdog/watchdog-parameters.rst
> @@ -515,6 +515,8 @@ sbsa_gwdt:
>      nowayout:
>  	Watchdog cannot be stopped once started
>  	(default=kernel config parameter)
> +    early_enable:
> +	Watchdog is started on module insertion (default=0)
>  
>  -------------------------------------------------
>  
> diff --git a/drivers/watchdog/sbsa_gwdt.c b/drivers/watchdog/sbsa_gwdt.c
> index e04d42cc7774..ed913be3d1cb 100644
> --- a/drivers/watchdog/sbsa_gwdt.c
> +++ b/drivers/watchdog/sbsa_gwdt.c
> @@ -122,6 +122,11 @@ MODULE_PARM_DESC(nowayout,
>  		 "Watchdog cannot be stopped once started (default="
>  		 __MODULE_STRING(WATCHDOG_NOWAYOUT) ")");
>  
> +static bool early_enable;
> +module_param(early_enable, bool, 0);
> +MODULE_PARM_DESC(early_enable,
> +		 "Watchdog is started on module insertion (default=0)");
> +
>  /*
>   * Arm Base System Architecture 1.0 introduces watchdog v1 which
>   * increases the length watchdog offset register to 48 bits.
> @@ -296,6 +301,7 @@ static int sbsa_gwdt_probe(struct platform_device *pdev)
>  	struct sbsa_gwdt *gwdt;
>  	int ret, irq;
>  	u32 status;
> +	bool early_action;
>  
>  	gwdt = devm_kzalloc(dev, sizeof(*gwdt), GFP_KERNEL);
>  	if (!gwdt)
> @@ -386,14 +392,27 @@ static int sbsa_gwdt_probe(struct platform_device *pdev)
>  	 */
>  	sbsa_gwdt_set_timeout(wdd, wdd->timeout);
>  
> +	early_action = early_enable && !(status & SBSA_GWDT_WCS_EN);
> +	if (early_action) {
> +		sbsa_gwdt_start(wdd);
> +		set_bit(WDOG_HW_RUNNING, &wdd->status);
> +		dev_info(dev, "Watchdog early enabled.\n");

Still unnecessary noise.

> +	}
> +
>  	watchdog_stop_on_reboot(wdd);
>  	ret = devm_watchdog_register_device(dev, wdd);
> -	if (ret)
> +	if (ret) {
> +		dev_err(dev, "Failed to register watchdog: %d\n", ret);

Still unrelated.

> +		if (early_action) {
> +			clear_bit(WDOG_HW_RUNNING, &wdd->status);

Still pointless / unnecessary.

> +			sbsa_gwdt_stop(wdd);
> +		}
>  		return ret;
> +	}
>  
>  	dev_info(dev, "Initialized with %ds timeout @ %u Hz, action=%d.%s\n",
>  		 wdd->timeout, gwdt->clk, action,
> -		 status & SBSA_GWDT_WCS_EN ? " [enabled]" : "");
> +		 watchdog_hw_running(wdd) ? " [enabled]" : "");
>  
>  	return 0;
>  }