2011-07-23 02:55:18 +08:00
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The Linux WatchDog Timer Driver Core kernel API.
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===============================================
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2013-01-08 18:04:10 +08:00
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Last reviewed: 12-Feb-2013
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2011-07-23 02:55:18 +08:00
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Wim Van Sebroeck <wim@iguana.be>
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Introduction
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------------
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This document does not describe what a WatchDog Timer (WDT) Driver or Device is.
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It also does not describe the API which can be used by user space to communicate
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with a WatchDog Timer. If you want to know this then please read the following
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file: Documentation/watchdog/watchdog-api.txt .
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So what does this document describe? It describes the API that can be used by
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WatchDog Timer Drivers that want to use the WatchDog Timer Driver Core
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Framework. This framework provides all interfacing towards user space so that
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the same code does not have to be reproduced each time. This also means that
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a watchdog timer driver then only needs to provide the different routines
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(operations) that control the watchdog timer (WDT).
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The API
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-------
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Each watchdog timer driver that wants to use the WatchDog Timer Driver Core
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must #include <linux/watchdog.h> (you would have to do this anyway when
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writing a watchdog device driver). This include file contains following
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register/unregister routines:
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extern int watchdog_register_device(struct watchdog_device *);
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extern void watchdog_unregister_device(struct watchdog_device *);
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The watchdog_register_device routine registers a watchdog timer device.
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The parameter of this routine is a pointer to a watchdog_device structure.
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This routine returns zero on success and a negative errno code for failure.
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The watchdog_unregister_device routine deregisters a registered watchdog timer
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device. The parameter of this routine is the pointer to the registered
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watchdog_device structure.
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2015-06-10 00:55:02 +08:00
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The watchdog subsystem includes an registration deferral mechanism,
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which allows you to register an watchdog as early as you wish during
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the boot process.
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2011-07-23 02:55:18 +08:00
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The watchdog device structure looks like this:
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struct watchdog_device {
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2012-05-11 03:48:59 +08:00
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int id;
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2012-05-11 18:00:20 +08:00
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struct device *dev;
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struct device *parent;
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2011-07-23 02:55:18 +08:00
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const struct watchdog_info *info;
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const struct watchdog_ops *ops;
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2011-07-23 02:56:38 +08:00
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unsigned int bootstatus;
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2011-07-23 02:58:21 +08:00
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unsigned int timeout;
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2011-07-23 03:00:16 +08:00
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unsigned int min_timeout;
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unsigned int max_timeout;
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2015-11-21 05:54:51 +08:00
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struct notifier_block reboot_nb;
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2015-11-17 01:27:59 +08:00
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struct notifier_block restart_nb;
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2011-07-23 02:55:18 +08:00
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void *driver_data;
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watchdog: Separate and maintain variables based on variable lifetime
All variables required by the watchdog core to manage a watchdog are
currently stored in struct watchdog_device. The lifetime of those
variables is determined by the watchdog driver. However, the lifetime
of variables used by the watchdog core differs from the lifetime of
struct watchdog_device. To remedy this situation, watchdog drivers
can implement ref and unref callbacks, to be used by the watchdog
core to lock struct watchdog_device in memory.
While this solves the immediate problem, it depends on watchdog drivers
to actually implement the ref/unref callbacks. This is error prone,
often not implemented in the first place, or not implemented correctly.
To solve the problem without requiring driver support, split the variables
in struct watchdog_device into two data structures - one for variables
associated with the watchdog driver, one for variables associated with
the watchdog core. With this approach, the watchdog core can keep track
of its variable lifetime and no longer depends on ref/unref callbacks
in the driver. As a side effect, some of the variables originally in
struct watchdog_driver are now private to the watchdog core and no longer
visible in watchdog drivers.
As a side effect of the changes made, an ioctl will now always fail
with -ENODEV after a watchdog device was unregistered with the character
device still open. Previously, it would only fail with -ENODEV in some
situations. Also, ioctl operations are now atomic from driver perspective.
With this change, it is now guaranteed that the driver will not unregister
a watchdog between a timeout change and the subsequent ping.
The 'ref' and 'unref' callbacks in struct watchdog_driver are no longer
used and marked as deprecated.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
2015-12-26 08:01:42 +08:00
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struct watchdog_core_data *wd_data;
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2011-07-23 02:55:18 +08:00
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unsigned long status;
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2015-06-10 00:55:02 +08:00
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struct list_head deferred;
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2011-07-23 02:55:18 +08:00
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};
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It contains following fields:
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2012-05-11 03:48:59 +08:00
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* id: set by watchdog_register_device, id 0 is special. It has both a
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/dev/watchdog0 cdev (dynamic major, minor 0) as well as the old
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/dev/watchdog miscdev. The id is set automatically when calling
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watchdog_register_device.
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2012-05-11 18:00:20 +08:00
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* dev: device under the watchdog class (created by watchdog_register_device).
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* parent: set this to the parent device (or NULL) before calling
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watchdog_register_device.
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2011-07-23 02:55:18 +08:00
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* info: a pointer to a watchdog_info structure. This structure gives some
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additional information about the watchdog timer itself. (Like it's unique name)
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* ops: a pointer to the list of watchdog operations that the watchdog supports.
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2011-07-23 02:58:21 +08:00
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* timeout: the watchdog timer's timeout value (in seconds).
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2011-07-23 03:00:16 +08:00
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* min_timeout: the watchdog timer's minimum timeout value (in seconds).
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* max_timeout: the watchdog timer's maximum timeout value (in seconds).
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2015-11-21 05:54:51 +08:00
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* reboot_nb: notifier block that is registered for reboot notifications, for
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internal use only. If the driver calls watchdog_stop_on_reboot, watchdog core
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will stop the watchdog on such notifications.
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2015-11-17 01:27:59 +08:00
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* restart_nb: notifier block that is registered for machine restart, for
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internal use only. If a watchdog is capable of restarting the machine, it
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should define ops->restart. Priority can be changed through
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watchdog_set_restart_priority.
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2011-07-23 02:56:38 +08:00
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* bootstatus: status of the device after booting (reported with watchdog
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WDIOF_* status bits).
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2011-07-23 02:55:18 +08:00
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* driver_data: a pointer to the drivers private data of a watchdog device.
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2012-05-14 17:03:37 +08:00
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This data should only be accessed via the watchdog_set_drvdata and
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2011-07-23 02:55:18 +08:00
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watchdog_get_drvdata routines.
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watchdog: Separate and maintain variables based on variable lifetime
All variables required by the watchdog core to manage a watchdog are
currently stored in struct watchdog_device. The lifetime of those
variables is determined by the watchdog driver. However, the lifetime
of variables used by the watchdog core differs from the lifetime of
struct watchdog_device. To remedy this situation, watchdog drivers
can implement ref and unref callbacks, to be used by the watchdog
core to lock struct watchdog_device in memory.
While this solves the immediate problem, it depends on watchdog drivers
to actually implement the ref/unref callbacks. This is error prone,
often not implemented in the first place, or not implemented correctly.
To solve the problem without requiring driver support, split the variables
in struct watchdog_device into two data structures - one for variables
associated with the watchdog driver, one for variables associated with
the watchdog core. With this approach, the watchdog core can keep track
of its variable lifetime and no longer depends on ref/unref callbacks
in the driver. As a side effect, some of the variables originally in
struct watchdog_driver are now private to the watchdog core and no longer
visible in watchdog drivers.
As a side effect of the changes made, an ioctl will now always fail
with -ENODEV after a watchdog device was unregistered with the character
device still open. Previously, it would only fail with -ENODEV in some
situations. Also, ioctl operations are now atomic from driver perspective.
With this change, it is now guaranteed that the driver will not unregister
a watchdog between a timeout change and the subsequent ping.
The 'ref' and 'unref' callbacks in struct watchdog_driver are no longer
used and marked as deprecated.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
2015-12-26 08:01:42 +08:00
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* wd_data: a pointer to watchdog core internal data.
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2011-07-23 02:55:18 +08:00
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* status: this field contains a number of status bits that give extra
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2011-07-23 02:57:55 +08:00
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information about the status of the device (Like: is the watchdog timer
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watchdog: Separate and maintain variables based on variable lifetime
All variables required by the watchdog core to manage a watchdog are
currently stored in struct watchdog_device. The lifetime of those
variables is determined by the watchdog driver. However, the lifetime
of variables used by the watchdog core differs from the lifetime of
struct watchdog_device. To remedy this situation, watchdog drivers
can implement ref and unref callbacks, to be used by the watchdog
core to lock struct watchdog_device in memory.
While this solves the immediate problem, it depends on watchdog drivers
to actually implement the ref/unref callbacks. This is error prone,
often not implemented in the first place, or not implemented correctly.
To solve the problem without requiring driver support, split the variables
in struct watchdog_device into two data structures - one for variables
associated with the watchdog driver, one for variables associated with
the watchdog core. With this approach, the watchdog core can keep track
of its variable lifetime and no longer depends on ref/unref callbacks
in the driver. As a side effect, some of the variables originally in
struct watchdog_driver are now private to the watchdog core and no longer
visible in watchdog drivers.
As a side effect of the changes made, an ioctl will now always fail
with -ENODEV after a watchdog device was unregistered with the character
device still open. Previously, it would only fail with -ENODEV in some
situations. Also, ioctl operations are now atomic from driver perspective.
With this change, it is now guaranteed that the driver will not unregister
a watchdog between a timeout change and the subsequent ping.
The 'ref' and 'unref' callbacks in struct watchdog_driver are no longer
used and marked as deprecated.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
2015-12-26 08:01:42 +08:00
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running/active, or is the nowayout bit set).
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2015-06-10 00:55:02 +08:00
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* deferred: entry in wtd_deferred_reg_list which is used to
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register early initialized watchdogs.
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2011-07-23 02:55:18 +08:00
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The list of watchdog operations is defined as:
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struct watchdog_ops {
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struct module *owner;
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/* mandatory operations */
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int (*start)(struct watchdog_device *);
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int (*stop)(struct watchdog_device *);
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/* optional operations */
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int (*ping)(struct watchdog_device *);
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2011-07-23 02:56:38 +08:00
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unsigned int (*status)(struct watchdog_device *);
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2011-07-23 02:58:21 +08:00
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int (*set_timeout)(struct watchdog_device *, unsigned int);
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2012-03-16 16:14:00 +08:00
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unsigned int (*get_timeleft)(struct watchdog_device *);
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2015-11-17 01:27:59 +08:00
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int (*restart)(struct watchdog_device *);
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watchdog: Separate and maintain variables based on variable lifetime
All variables required by the watchdog core to manage a watchdog are
currently stored in struct watchdog_device. The lifetime of those
variables is determined by the watchdog driver. However, the lifetime
of variables used by the watchdog core differs from the lifetime of
struct watchdog_device. To remedy this situation, watchdog drivers
can implement ref and unref callbacks, to be used by the watchdog
core to lock struct watchdog_device in memory.
While this solves the immediate problem, it depends on watchdog drivers
to actually implement the ref/unref callbacks. This is error prone,
often not implemented in the first place, or not implemented correctly.
To solve the problem without requiring driver support, split the variables
in struct watchdog_device into two data structures - one for variables
associated with the watchdog driver, one for variables associated with
the watchdog core. With this approach, the watchdog core can keep track
of its variable lifetime and no longer depends on ref/unref callbacks
in the driver. As a side effect, some of the variables originally in
struct watchdog_driver are now private to the watchdog core and no longer
visible in watchdog drivers.
As a side effect of the changes made, an ioctl will now always fail
with -ENODEV after a watchdog device was unregistered with the character
device still open. Previously, it would only fail with -ENODEV in some
situations. Also, ioctl operations are now atomic from driver perspective.
With this change, it is now guaranteed that the driver will not unregister
a watchdog between a timeout change and the subsequent ping.
The 'ref' and 'unref' callbacks in struct watchdog_driver are no longer
used and marked as deprecated.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
2015-12-26 08:01:42 +08:00
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void (*ref)(struct watchdog_device *) __deprecated;
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void (*unref)(struct watchdog_device *) __deprecated;
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2011-07-23 02:59:49 +08:00
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long (*ioctl)(struct watchdog_device *, unsigned int, unsigned long);
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2011-07-23 02:55:18 +08:00
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};
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It is important that you first define the module owner of the watchdog timer
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driver's operations. This module owner will be used to lock the module when
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the watchdog is active. (This to avoid a system crash when you unload the
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module and /dev/watchdog is still open).
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2012-05-22 17:40:26 +08:00
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2011-07-23 02:55:18 +08:00
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Some operations are mandatory and some are optional. The mandatory operations
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are:
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* start: this is a pointer to the routine that starts the watchdog timer
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device.
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The routine needs a pointer to the watchdog timer device structure as a
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parameter. It returns zero on success or a negative errno code for failure.
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* stop: with this routine the watchdog timer device is being stopped.
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The routine needs a pointer to the watchdog timer device structure as a
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parameter. It returns zero on success or a negative errno code for failure.
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Some watchdog timer hardware can only be started and not be stopped. The
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driver supporting this hardware needs to make sure that a start and stop
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routine is being provided. This can be done by using a timer in the driver
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that regularly sends a keepalive ping to the watchdog timer hardware.
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Not all watchdog timer hardware supports the same functionality. That's why
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all other routines/operations are optional. They only need to be provided if
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they are supported. These optional routines/operations are:
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* ping: this is the routine that sends a keepalive ping to the watchdog timer
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hardware.
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The routine needs a pointer to the watchdog timer device structure as a
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parameter. It returns zero on success or a negative errno code for failure.
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Most hardware that does not support this as a separate function uses the
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start function to restart the watchdog timer hardware. And that's also what
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the watchdog timer driver core does: to send a keepalive ping to the watchdog
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timer hardware it will either use the ping operation (when available) or the
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start operation (when the ping operation is not available).
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2011-07-23 02:57:23 +08:00
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(Note: the WDIOC_KEEPALIVE ioctl call will only be active when the
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WDIOF_KEEPALIVEPING bit has been set in the option field on the watchdog's
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info structure).
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2011-07-23 02:56:38 +08:00
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* status: this routine checks the status of the watchdog timer device. The
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status of the device is reported with watchdog WDIOF_* status flags/bits.
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2011-07-23 02:58:21 +08:00
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* set_timeout: this routine checks and changes the timeout of the watchdog
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timer device. It returns 0 on success, -EINVAL for "parameter out of range"
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2011-09-12 17:56:59 +08:00
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and -EIO for "could not write value to the watchdog". On success this
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routine should set the timeout value of the watchdog_device to the
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achieved timeout value (which may be different from the requested one
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because the watchdog does not necessarily has a 1 second resolution).
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2011-07-23 02:58:21 +08:00
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(Note: the WDIOF_SETTIMEOUT needs to be set in the options field of the
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watchdog's info structure).
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2012-03-16 16:14:00 +08:00
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* get_timeleft: this routines returns the time that's left before a reset.
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2015-11-17 01:27:59 +08:00
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* restart: this routine restarts the machine. It returns 0 on success or a
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negative errno code for failure.
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2011-07-23 02:59:49 +08:00
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* ioctl: if this routine is present then it will be called first before we do
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our own internal ioctl call handling. This routine should return -ENOIOCTLCMD
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if a command is not supported. The parameters that are passed to the ioctl
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call are: watchdog_device, cmd and arg.
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2011-07-23 02:55:18 +08:00
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watchdog: Separate and maintain variables based on variable lifetime
All variables required by the watchdog core to manage a watchdog are
currently stored in struct watchdog_device. The lifetime of those
variables is determined by the watchdog driver. However, the lifetime
of variables used by the watchdog core differs from the lifetime of
struct watchdog_device. To remedy this situation, watchdog drivers
can implement ref and unref callbacks, to be used by the watchdog
core to lock struct watchdog_device in memory.
While this solves the immediate problem, it depends on watchdog drivers
to actually implement the ref/unref callbacks. This is error prone,
often not implemented in the first place, or not implemented correctly.
To solve the problem without requiring driver support, split the variables
in struct watchdog_device into two data structures - one for variables
associated with the watchdog driver, one for variables associated with
the watchdog core. With this approach, the watchdog core can keep track
of its variable lifetime and no longer depends on ref/unref callbacks
in the driver. As a side effect, some of the variables originally in
struct watchdog_driver are now private to the watchdog core and no longer
visible in watchdog drivers.
As a side effect of the changes made, an ioctl will now always fail
with -ENODEV after a watchdog device was unregistered with the character
device still open. Previously, it would only fail with -ENODEV in some
situations. Also, ioctl operations are now atomic from driver perspective.
With this change, it is now guaranteed that the driver will not unregister
a watchdog between a timeout change and the subsequent ping.
The 'ref' and 'unref' callbacks in struct watchdog_driver are no longer
used and marked as deprecated.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
2015-12-26 08:01:42 +08:00
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The 'ref' and 'unref' operations are no longer used and deprecated.
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2011-07-23 02:55:18 +08:00
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The status bits should (preferably) be set with the set_bit and clear_bit alike
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bit-operations. The status bits that are defined are:
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2011-07-23 02:57:55 +08:00
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* WDOG_ACTIVE: this status bit indicates whether or not a watchdog timer device
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is active or not. When the watchdog is active after booting, then you should
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set this status bit (Note: when you register the watchdog timer device with
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this bit set, then opening /dev/watchdog will skip the start operation)
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2011-07-23 02:59:17 +08:00
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* WDOG_NO_WAY_OUT: this bit stores the nowayout setting for the watchdog.
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If this bit is set then the watchdog timer will not be able to stop.
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2011-07-23 02:58:54 +08:00
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2011-11-29 23:24:16 +08:00
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To set the WDOG_NO_WAY_OUT status bit (before registering your watchdog
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timer device) you can either:
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* set it statically in your watchdog_device struct with
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.status = WATCHDOG_NOWAYOUT_INIT_STATUS,
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(this will set the value the same as CONFIG_WATCHDOG_NOWAYOUT) or
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* use the following helper function:
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static inline void watchdog_set_nowayout(struct watchdog_device *wdd, int nowayout)
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2011-07-23 02:59:17 +08:00
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Note: The WatchDog Timer Driver Core supports the magic close feature and
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the nowayout feature. To use the magic close feature you must set the
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WDIOF_MAGICCLOSE bit in the options field of the watchdog's info structure.
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The nowayout feature will overrule the magic close feature.
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2011-07-23 02:55:18 +08:00
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To get or set driver specific data the following two helper functions should be
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used:
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static inline void watchdog_set_drvdata(struct watchdog_device *wdd, void *data)
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static inline void *watchdog_get_drvdata(struct watchdog_device *wdd)
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The watchdog_set_drvdata function allows you to add driver specific data. The
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arguments of this function are the watchdog device where you want to add the
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driver specific data to and a pointer to the data itself.
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The watchdog_get_drvdata function allows you to retrieve driver specific data.
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The argument of this function is the watchdog device where you want to retrieve
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2012-02-10 23:09:20 +08:00
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data from. The function returns the pointer to the driver specific data.
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2013-01-08 18:04:10 +08:00
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To initialize the timeout field, the following function can be used:
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extern int watchdog_init_timeout(struct watchdog_device *wdd,
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unsigned int timeout_parm, struct device *dev);
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The watchdog_init_timeout function allows you to initialize the timeout field
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using the module timeout parameter or by retrieving the timeout-sec property from
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the device tree (if the module timeout parameter is invalid). Best practice is
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to set the default timeout value as timeout value in the watchdog_device and
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then use this function to set the user "preferred" timeout value.
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This routine returns zero on success and a negative errno code for failure.
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2015-11-17 01:27:59 +08:00
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2015-11-21 05:54:51 +08:00
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To disable the watchdog on reboot, the user must call the following helper:
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static inline void watchdog_stop_on_reboot(struct watchdog_device *wdd);
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2015-11-17 01:27:59 +08:00
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To change the priority of the restart handler the following helper should be
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used:
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void watchdog_set_restart_priority(struct watchdog_device *wdd, int priority);
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User should follow the following guidelines for setting the priority:
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* 0: should be called in last resort, has limited restart capabilities
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* 128: default restart handler, use if no other handler is expected to be
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available, and/or if restart is sufficient to restart the entire system
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* 255: highest priority, will preempt all other restart handlers
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