linux-kernel - RE: [PATCH v1] watchdog: add new parameter to start the watchdog on module insertion

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Message-ID: <98f7ca84e44e4625b54e1aecef88f238@asem.it>
Date:   Mon, 12 Apr 2021 08:29:45 +0000
From:   Flavio Suligoi <f.suligoi@...m.it>
To:     Guenter Roeck <linux@...ck-us.net>
CC:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Wim Van Sebroeck" <wim@...ux-watchdog.org>
Subject: RE: [PATCH v1] watchdog: add new parameter to start the watchdog on
 module insertion

Hi Guenter,

...

> On 4/9/21 2:34 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 function can be also enabled in the kernel config, so can be
> > 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.
> >
> > Note: to use only for watchdog drivers which doesn't support this
> >       parameter by itself.
> >
> > Signed-off-by: Flavio Suligoi <f.suligoi@...m.it>
> > ---
> >  Documentation/watchdog/watchdog-parameters.rst |  5 +++++
> >  drivers/watchdog/Kconfig                       | 14 ++++++++++++++
> >  drivers/watchdog/watchdog_core.c               | 12 ++++++++++++
> >  3 files changed, 31 insertions(+)
> >
> > diff --git a/Documentation/watchdog/watchdog-parameters.rst
> b/Documentation/watchdog/watchdog-parameters.rst
> > index 223c99361a30..623fd064df91 100644
> > --- a/Documentation/watchdog/watchdog-parameters.rst
> > +++ b/Documentation/watchdog/watchdog-parameters.rst
> > @@ -21,6 +21,11 @@ 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).
> > +	Use only for watchdog drivers which doesn't support this parameter
> > +	by itself.
> 
> Why ?

There are two drivers with an analogous feature (pnx833x_wdt and
omap_wdt) and it is important not to enable the watchdog twice.

Ok, I can substitute the sentence: " Use only for watchdog drivers
which doesn't support this parameter itself." with another one, like:
"If the driver supports this feature by itself, be carefully not to enable
the watchdog twice".

What do you think?

> 
> >
> >  -------------------------------------------------
> >
> > diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> > index 0470dc15c085..c2a668d6bbbc 100644
> > --- a/drivers/watchdog/Kconfig
> > +++ b/drivers/watchdog/Kconfig
> > @@ -47,6 +47,20 @@ 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 involves the "core" section of the watchdog driver,
> > +	  in this way it is common for all the watchdog hardware
> > +	  implementations.
> 
> "This parameter applies to all watchdog drivers.". The rest is implementation
> detail and irrelevant here.

Ok

> 
> > +
> > +	  Note: to use only for watchdog drivers which doesn't support this
> > +	        parameter by itself.
> > +
> 
> This comment is quite useless in the Kconfig description. If enabled, it is enabled,
> period.

Ok, I'll remove this comment.

> 
> >  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 5df0a22e2cb4..5052ae355219 100644
> > --- a/drivers/watchdog/watchdog_core.c
> > +++ b/drivers/watchdog/watchdog_core.c
> > @@ -43,6 +43,11 @@ 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_ENABL
> ED)) ")");
> > +
> >  /*
> >   * Deferred Registration infrastructure.
> >   *
> > @@ -224,6 +229,13 @@ 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) {
> > +		set_bit(WDOG_HW_RUNNING, &wdd->status);
> > +		wdd->ops->start(wdd);
> > +		pr_info("Watchdog enabled\n");
> > +	}
> > +
> >  	/* Use alias for watchdog id if possible */
> >  	if (wdd->parent) {
> >  		ret = of_alias_get_id(wdd->parent->of_node, "watchdog");
> >

Best regards,
Flavio Suligoi