linux-imx

The Linux WatchDog Timer Driver Core kernel API.

===============================================

Last reviewed: 12-Feb-2013

​

Wim Van Sebroeck <wim@iguana.be>

​

Introduction

------------

This document does not describe what a WatchDog Timer (WDT) Driver or Device is.

It also does not describe the API which can be used by user space to communicate

with a WatchDog Timer. If you want to know this then please read the following

file: Documentation/watchdog/watchdog-api.txt .

​

So what does this document describe? It describes the API that can be used by

WatchDog Timer Drivers that want to use the WatchDog Timer Driver Core

Framework. This framework provides all interfacing towards user space so that

the same code does not have to be reproduced each time. This also means that

a watchdog timer driver then only needs to provide the different routines

(operations) that control the watchdog timer (WDT).

​

The API

-------

Each watchdog timer driver that wants to use the WatchDog Timer Driver Core

must #include <linux/watchdog.h> (you would have to do this anyway when

writing a watchdog device driver). This include file contains following

register/unregister routines:

​

extern int watchdog_register_device(struct watchdog_device *);

extern void watchdog_unregister_device(struct watchdog_device *);

​

The watchdog_register_device routine registers a watchdog timer device.

The parameter of this routine is a pointer to a watchdog_device structure.

This routine returns zero on success and a negative errno code for failure.

​

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 {

    int id;

    struct device *parent;

    const struct attribute_group **groups;

    const struct watchdog_info *info;

    const struct watchdog_ops *ops;

    const struct watchdog_governor *gov;

    unsigned int bootstatus;

    unsigned int timeout;

    unsigned int pretimeout;

    unsigned int min_timeout;

    unsigned int max_timeout;

    unsigned int min_hw_heartbeat_ms;

    unsigned int max_hw_heartbeat_ms;

    struct notifier_block reboot_nb;

    struct notifier_block restart_nb;

    void *driver_data;

    struct watchdog_core_data *wd_data;

    unsigned long status;