Date:	Sat, 06 Jun 2015 10:00:10 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Jean-Baptiste Theou <jtheou@...neo-embedded.us>,
	Wim Van Sebroeck <wim@...ana.be>
CC:	linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] watchdog_core: Add watchdog registration deferral
 mechanism

On 06/06/2015 12:46 AM, Jean-Baptiste Theou wrote:
> Currently, watchdog subsystem require the misc subsystem to
> register a watchdog. This may not be the case in case of an
> early registration of a watchdog, which can be required when
> the watchdog cannot be disabled.
>
> This patch introduces a deferral mechanism to remove this requirement.
>
Couple of comments, but almost good.

Thanks,
Guenter

> Signed-off-by: Jean-Baptiste Theou <jtheou@...neo-embedded.us>
> ---
> Changes in v3:
>   - Adjust patch based on Guenter feedbacks
>   - Fix watchdog_deferred_registration_del
>   - Fix typos
>
>   Documentation/watchdog/watchdog-kernel-api.txt |   7 ++
>   drivers/watchdog/watchdog_core.c               | 114 +++++++++++++++++++++----
>   include/linux/watchdog.h                       |   3 +
>   3 files changed, 106 insertions(+), 18 deletions(-)
>
> diff --git a/Documentation/watchdog/watchdog-kernel-api.txt b/Documentation/watchdog/watchdog-kernel-api.txt
> index a0438f3..e83518c 100644
> --- a/Documentation/watchdog/watchdog-kernel-api.txt
> +++ b/Documentation/watchdog/watchdog-kernel-api.txt
> @@ -36,6 +36,10 @@ The watchdog_unregister_device routine deregisters a registered watchdog timer
>   device. The parameter of this routine is the pointer to the registered
>   watchdog_device structure.
>
> +The watchdog subsystem includes an registration deferral mechanism,
> +which allows you to register an watchdog as early as you wish during
> +the boot process.
> +
>   The watchdog device structure looks like this:
>
>   struct watchdog_device {
> @@ -52,6 +56,7 @@ struct watchdog_device {
>   	void *driver_data;
>   	struct mutex lock;
>   	unsigned long status;
> +	struct list_head deferred_registration;
>   };
>
>   It contains following fields:
> @@ -80,6 +85,8 @@ It contains following fields:
>     information about the status of the device (Like: is the watchdog timer
>     running/active, is the nowayout bit set, is the device opened via
>     the /dev/watchdog interface or not, ...).
> +* deferred_registration: entry in deferred_registration_list which is used to
> +  register early initialized watchdogs.
>
>   The list of watchdog operations is defined as:
>
> diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
> index cec9b55..7dba8d9 100644
> --- a/drivers/watchdog/watchdog_core.c
> +++ b/drivers/watchdog/watchdog_core.c
> @@ -43,6 +43,43 @@
>   static DEFINE_IDA(watchdog_ida);
>   static struct class *watchdog_class;
>
> +/*
> + * Deferred Registration infrastructure.
> + *
> + * Sometimes watchdog drivers needs to be loaded as soon as possible,
> + * for example when it's impossible to disable it. To do so,
> + * raising the initcall level of the watchdog driver is a solution.
> + * But in such case, the miscdev is maybe not ready (subsys_initcall), and
> + * watchdog_core need miscdev to register the watchdog as a char device.
> + *
> + * The deferred registration infrastructure offer a way for the watchdog
> + * subsystem to register a watchdog properly, even before miscdev is ready.
> + */
> +
> +static DEFINE_MUTEX(watchdog_deferred_registration_mutex);
> +static LIST_HEAD(watchdog_deferred_registration_pending_list);
> +static bool watchdog_deferred_registration_done;
> +
> +static int watchdog_deferred_registration_add(struct watchdog_device *wdd)
> +{
> +	list_add_tail(&wdd->deferred_registration,
> +		 &watchdog_deferred_registration_pending_list);

Please align the continuation line with '('.

> +	return 0;
> +}
> +
> +static void watchdog_deferred_registration_del(struct watchdog_device *wdd)
> +{
> +	struct list_head *p, *n;
> +	struct watchdog_device *wdd_tmp;
> +
> +	list_for_each_safe(p, n, &watchdog_deferred_registration_pending_list) {
> +		wdd_tmp = list_entry(p, struct watchdog_device,
> +				     deferred_registration);
> +		if (wdd_tmp == wdd)
> +			list_del(&wdd_tmp->deferred_registration);

You can break out of the loop here. No need to check the rest of the entries.

> +	}
> +}
> +
>   static void watchdog_check_min_max_timeout(struct watchdog_device *wdd)
>   {
>   	/*
> @@ -98,17 +135,7 @@ int watchdog_init_timeout(struct watchdog_device *wdd,
>   }
>   EXPORT_SYMBOL_GPL(watchdog_init_timeout);
>
> -/**
> - * watchdog_register_device() - register a watchdog device
> - * @wdd: watchdog device
> - *
> - * Register a watchdog device with the kernel so that the
> - * watchdog timer can be accessed from userspace.
> - *
> - * A zero is returned on success and a negative errno code for
> - * failure.
> - */
> -int watchdog_register_device(struct watchdog_device *wdd)
> +static int __watchdog_register_device(struct watchdog_device *wdd)
>   {
>   	int ret, id, devno;
>
> @@ -164,16 +191,33 @@ int watchdog_register_device(struct watchdog_device *wdd)
>
>   	return 0;
>   }
> -EXPORT_SYMBOL_GPL(watchdog_register_device);
>
>   /**
> - * watchdog_unregister_device() - unregister a watchdog device
> - * @wdd: watchdog device to unregister
> + * watchdog_register_device() - register a watchdog device
> + * @wdd: watchdog device
>    *
> - * Unregister a watchdog device that was previously successfully
> - * registered with watchdog_register_device().
> + * Register a watchdog device with the kernel so that the
> + * watchdog timer can be accessed from userspace.
> + *
> + * A zero is returned on success and a negative errno code for
> + * failure.
>    */
> -void watchdog_unregister_device(struct watchdog_device *wdd)
> +
> +int watchdog_register_device(struct watchdog_device *wdd)
> +{
> +	int ret;
> +
> +	mutex_lock(&watchdog_deferred_registration_mutex);
> +	if (watchdog_deferred_registration_done)
> +		ret = __watchdog_register_device(wdd);
> +	else
> +		ret = watchdog_deferred_registration_add(wdd);
> +	mutex_unlock(&watchdog_deferred_registration_mutex);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(watchdog_register_device);
> +
> +static void __watchdog_unregister_device(struct watchdog_device *wdd)
>   {
>   	int ret;
>   	int devno;
> @@ -189,8 +233,41 @@ void watchdog_unregister_device(struct watchdog_device *wdd)
>   	ida_simple_remove(&watchdog_ida, wdd->id);
>   	wdd->dev = NULL;
>   }
> +
> +/**
> + * watchdog_unregister_device() - unregister a watchdog device
> + * @wdd: watchdog device to unregister
> + *
> + * Unregister a watchdog device that was previously successfully
> + * registered with watchdog_register_device().
> + */
> +
> +void watchdog_unregister_device(struct watchdog_device *wdd)
> +{
> +	mutex_lock(&watchdog_deferred_registration_mutex);
> +	if (watchdog_deferred_registration_done)
> +		__watchdog_unregister_device(wdd);
> +	else
> +		watchdog_deferred_registration_del(wdd);
> +	mutex_unlock(&watchdog_deferred_registration_mutex);
> +}
> +
>   EXPORT_SYMBOL_GPL(watchdog_unregister_device);
>
> +static int __init watchdog_deferred_registration(void)
> +{
> +	mutex_lock(&watchdog_deferred_registration_mutex);
> +	watchdog_deferred_registration_done = true;
> +	while (!list_empty(&watchdog_deferred_registration_pending_list)) {
> +		struct watchdog_device *wdd = list_first_entry(&watchdog_deferred_registration_pending_list,
> +							       struct watchdog_device, deferred_registration);

Please watch out for line length.

		struct watchdog_device *wdd;

		wdd = list_first_entry(&watchdog_deferred_registration_pending_list,
			               struct watchdog_device, deferred_registration);

might work better here.

> +		list_del(&wdd->deferred_registration);
> +		__watchdog_register_device(wdd);
> +	}
> +	mutex_unlock(&watchdog_deferred_registration_mutex);
> +	return 0;
> +}
> +
>   static int __init watchdog_init(void)
>   {
>   	int err;
> @@ -207,6 +284,7 @@ static int __init watchdog_init(void)
>   		return err;
>   	}
>
> +	watchdog_deferred_registration();
>   	return 0;
>   }
>
> @@ -217,7 +295,7 @@ static void __exit watchdog_exit(void)
>   	ida_destroy(&watchdog_ida);
>   }
>
> -subsys_initcall(watchdog_init);
> +subsys_initcall_sync(watchdog_init);
>   module_exit(watchdog_exit);
>
>   MODULE_AUTHOR("Alan Cox <alan@...rguk.ukuu.org.uk>");
> diff --git a/include/linux/watchdog.h b/include/linux/watchdog.h
> index a746bf5..f9bb943 100644
> --- a/include/linux/watchdog.h
> +++ b/include/linux/watchdog.h
> @@ -65,6 +65,8 @@ struct watchdog_ops {
>    * @driver-data:Pointer to the drivers private data.
>    * @lock:	Lock for watchdog core internal use only.
>    * @status:	Field that contains the devices internal status bits.
> + * @deferred_registration: entry in deferred_registration_list which is used to
> + *			   register early initialized watchdogs.
>    *
>    * The watchdog_device structure contains all information about a
>    * watchdog timer device.
> @@ -95,6 +97,7 @@ struct watchdog_device {
>   #define WDOG_ALLOW_RELEASE	2	/* Did we receive the magic char ? */
>   #define WDOG_NO_WAY_OUT		3	/* Is 'nowayout' feature set ? */
>   #define WDOG_UNREGISTERED	4	/* Has the device been unregistered */
> +	struct list_head deferred_registration;
>   };
>
>   #define WATCHDOG_NOWAYOUT		IS_BUILTIN(CONFIG_WATCHDOG_NOWAYOUT)
>

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists