linux-kernel - Re: [PATCH v3] watchdog: add new parameter to start the watchdog on module insertion

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Date:   Fri, 17 Sep 2021 07:45:22 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Flavio Suligoi <f.suligoi@...m.it>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>
Cc:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] watchdog: add new parameter to start the watchdog on
 module insertion

On 9/16/21 7:40 AM, Flavio Suligoi wrote:
> The new parameter "start_enabled" starts the watchdog at the same time
> of the module insertion.
> This feature is very useful in embedded systems, to avoid cases where
> the system hangs before reaching userspace.
> 
> This feature can be enabled in the kernel config, so it can be also
> used when the watchdog driver is build as "built-in".
> 
> This parameter involves the "core" section of the watchdog driver;
> in this way it is common for all the watchdog hardware implementations.
> 
> Signed-off-by: Flavio Suligoi <f.suligoi@...m.it>
> ---
> 
> v3: - add check for the returned error of wdog start function
> v2: - check WDOG_HW_RUNNING before starting watchdog;
>      - remove useless comments in commit text, watchdog-parameters.rst and
>        Kconfig;
> v1: - first version;
> 
>   Documentation/watchdog/watchdog-parameters.rst |  3 +++
>   drivers/watchdog/Kconfig                       |  9 +++++++++
>   drivers/watchdog/watchdog_core.c               | 16 ++++++++++++++++
>   3 files changed, 28 insertions(+)
> 
> diff --git a/Documentation/watchdog/watchdog-parameters.rst b/Documentation/watchdog/watchdog-parameters.rst
> index 223c99361a30..7780d0c1fb4a 100644
> --- a/Documentation/watchdog/watchdog-parameters.rst
> +++ b/Documentation/watchdog/watchdog-parameters.rst
> @@ -21,6 +21,9 @@ watchdog core:
>   	timeout. Setting this to a non-zero value can be useful to ensure that
>   	either userspace comes up properly, or the board gets reset and allows
>   	fallback logic in the bootloader to try something else.
> +    start_enabled:
> +	Watchdog is started on module insertion. This option can be also
> +	selected by kernel config (default=kernel config parameter).
>   
>   -------------------------------------------------
>   
> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> index b81fe4f7d434..19be709e01ac 100644
> --- a/drivers/watchdog/Kconfig
> +++ b/drivers/watchdog/Kconfig
> @@ -47,6 +47,15 @@ config WATCHDOG_NOWAYOUT
>   	  get killed. If you say Y here, the watchdog cannot be stopped once
>   	  it has been started.
>   
> +config WATCHDOG_START_ENABLED
> +	bool "Start watchdog on module insertion"
> +	help
> +	  Say Y if you want to start the watchdog at the same time when the
> +	  driver is loaded.
> +	  This feature is very useful in embedded systems, to avoid cases where
> +	  the system could hang before reaching userspace.
> +	  This parameter applies to all watchdog drivers.
> +
>   config WATCHDOG_HANDLE_BOOT_ENABLED
>   	bool "Update boot-enabled watchdog until userspace takes over"
>   	default y
> diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
> index 3fe8a7edc252..cb530b097223 100644
> --- a/drivers/watchdog/watchdog_core.c
> +++ b/drivers/watchdog/watchdog_core.c
> @@ -44,6 +44,11 @@ static int stop_on_reboot = -1;
>   module_param(stop_on_reboot, int, 0444);
>   MODULE_PARM_DESC(stop_on_reboot, "Stop watchdogs on reboot (0=keep watching, 1=stop)");
>   
> +static bool start_enabled = IS_ENABLED(CONFIG_WATCHDOG_START_ENABLED);
> +module_param(start_enabled, bool, 0444);
> +MODULE_PARM_DESC(start_enabled, "Start watchdog on module insertion (default="
> +	__MODULE_STRING(IS_ENABLED(CONFIG_WATCHDOG_START_ENABLED)) ")");
> +
>   /*
>    * Deferred Registration infrastructure.
>    *
> @@ -252,6 +257,17 @@ static int __watchdog_register_device(struct watchdog_device *wdd)
>   	 * corrupted in a later stage then we expect a kernel panic!
>   	 */
>   
> +	/* If required, start the watchdog immediately */
> +	if (start_enabled && !watchdog_hw_running(wdd)) {
> +		set_bit(WDOG_HW_RUNNING, &wdd->status);
> +		ret = wdd->ops->start(wdd);
> +		if (ret == 0) {
> +			pr_info("Watchdog enabled\n");
> +		} else {
> +			return ret;
> +		}

This should be
		if (ret)
			return ret;
		pr_info("Watchdog enabled\n");

Also, this needs an error handler to stop the watchdog if driver registration
fails (if the driver supports stopping the watchdog).

Thanks,
Guenter

> +	}
> +
>   	/* Use alias for watchdog id if possible */
>   	if (wdd->parent) {
>   		ret = of_alias_get_id(wdd->parent->of_node, "watchdog");
>