linux的I2C驱动——ID匹配

以下基于3.0内核版本的源码进行讲解，驱动代码路径为drivers/misc/eeprom/at24.c。I2C核心代码路径为drivers/I2C

模块入口

module_init(at24_init);

module_init()是一个宏定义，位于include/linux/init.h。
如果将驱动编译入内核，定义如下：

#define device_initcall(fn)     __define_initcall("6",fn,6)#define __initcall(fn) device_initcall(fn)#define module_init(x)  __initcall(x);

这样在内核初始化的时候就会直接对该驱动进行初始化了。关于内核初始化部分，后续再讲述。
如果以模块方式编译，定义如下：

#define module_init(initfn)                 \    static inline initcall_t __inittest(void)       \    { return initfn; }                  \    int init_module(void) __attribute__((alias(#initfn)));

__inittest仅仅是为了检测定义的函数是否符合initcall_t类型，如果不是__inittest类型在编译时将会报错

模块初始化

/*drivers/misc/eeprom/at24.c*/static int __init at24_init(void){    if (!io_limit) {        pr_err("at24: io_limit must not be 0!\n");        return -EINVAL;    }    io_limit = rounddown_pow_of_two(io_limit);    return i2c_add_driver(&at24_driver);}

/*include/linux/i2c.h*/static inline int i2c_add_driver(struct i2c_driver *driver){    return i2c_register_driver(THIS_MODULE, driver);}

注册函数

/*drivers/i2c/i2c-core.c*/int i2c_register_driver(struct module *owner, struct i2c_driver *driver){    int res;    /* add the driver to the list of i2c drivers in the driver core */    driver->driver.owner = owner;    driver->driver.bus = &i2c_bus_type;    /* When registration returns, the driver core     * will have called probe() for all matching-but-unbound devices.     */    res = driver_register(&driver->driver);    ……    INIT_LIST_HEAD(&driver->clients);    /* Walk the adapters that are already present */    i2c_for_each_dev(driver, __process_new_driver);    return 0;}EXPORT_SYMBOL(i2c_register_driver);

调用driver_register函数在总线上注册驱动

/*drivers/base/driver.c*/int driver_register(struct device_driver *drv){    int ret;    struct device_driver *other;    ……    ret = bus_add_driver(drv);    if (ret)        return ret;    ret = driver_add_groups(drv, drv->groups);    if (ret)        bus_remove_driver(drv);    return ret;}EXPORT_SYMBOL_GPL(driver_register);

/*drivers/base/bus.c*/int bus_add_driver(struct device_driver *drv){    struct bus_type *bus;    struct driver_private *priv;    int error = 0;    bus = bus_get(drv->bus);    if (!bus)        return -EINVAL;    pr_debug("bus: '%s': add driver %s\n", bus->name, drv->name);    priv = kzalloc(sizeof(*priv), GFP_KERNEL);    if (!priv) {        error = -ENOMEM;        goto out_put_bus;    }    klist_init(&priv->klist_devices, NULL, NULL);    priv->driver = drv;    drv->p = priv;    priv->kobj.kset = bus->p->drivers_kset;    error = kobject_init_and_add(&priv->kobj, &driver_ktype, NULL,                     "%s", drv->name);//添加到总线链表    if (error)        goto out_unregister;    if (drv->bus->p->drivers_autoprobe) {        error = driver_attach(drv);        if (error)            goto out_unregister;    }    klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);    module_add_driver(drv->owner, drv);}

设备和驱动开始匹配

/*drivers/base/dd.c*/int driver_attach(struct device_driver *drv){    return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);}EXPORT_SYMBOL_GPL(driver_attach);

通过next_device函数进行设备搜索，然后再通过__driver_attach函数进行匹配。直到next_device函数搜索到匹配设备，或者到链表尾端。

/*drivers/base/bus.c*/int bus_for_each_dev(struct bus_type *bus, struct device *start,             void *data, int (*fn)(struct device *, void *)){    struct klist_iter i;    struct device *dev;    int error = 0;    if (!bus)        return -EINVAL;    klist_iter_init_node(&bus->p->klist_devices, &i,                 (start ? &start->p->knode_bus : NULL));    while ((dev = next_device(&i)) && !error)        error = fn(dev, data);    klist_iter_exit(&i);    return error;}

next_device通过链表查询设备

/*drivers/base/bus.c*/static struct device *next_device(struct klist_iter *i){    struct klist_node *n = klist_next(i);    struct device *dev = NULL;    struct device_private *dev_prv;    if (n) {        dev_prv = to_device_private_bus(n);        dev = dev_prv->device;    }    return dev;}

匹配函数，通过driver_match_device函数去匹配。匹配完会通过driver_probe_device函数去调用probe函数。

/*drivers/base/dd.c*/static int __driver_attach(struct device *dev, void *data){    struct device_driver *drv = data;    if (!driver_match_device(drv, dev))        return 0;    if (dev->parent)    /* Needed for USB */        device_lock(dev->parent);    device_lock(dev);    if (!dev->driver)        driver_probe_device(drv, dev);    device_unlock(dev);    if (dev->parent)        device_unlock(dev->parent);    return 0;}

这里来讲解一下，匹配对象。
主要涉及到以下几个参数：

/*drivers/misc/eeprom/at24.c*/static const struct i2c_device_id at24_ids[] = {    { "24c02", AT24_DEVICE_MAGIC(2048 / 8, 0) },    { "at24", 0 },    { /* END OF LIST */ }};MODULE_DEVICE_TABLE(i2c, at24_ids);static struct i2c_driver at24_driver = {    .driver = {        .name = "at24",        .owner = THIS_MODULE,    },    .probe = at24_probe,    .remove = __devexit_p(at24_remove),    .id_table = at24_ids,};

/*arch/arm/mach-xxx/mach_xxx.c*/static struct i2c_board_info at24xx[]={    {        I2C_BOARD_INFO("at24c02",0x50);    },};i2c_register_board_info(0,at24xx,ARRAY_SIZE(at24xx));

所谓的匹配是将i2c_driver和i2c_client进行匹配，主要是将at24_ids与at24xx进行匹配。接着回到上面的匹配函数。

/*drivers/base/base.h*/static inline int driver_match_device(struct device_driver *drv,                      struct device *dev){    return drv->bus->match ? drv->bus->match(dev, drv) : 1;}

在这里调用了总线的match函数。在i2c_register_driver函数中，已经定义了总线参数 driver->driver.bus = &i2c_bus_type
我们来看一下这个结构体，对应的函数。

/*drivers/I2C/i2c_core.c*/struct bus_type i2c_bus_type = {    .name       = "i2c",    .match      = i2c_device_match,    .probe      = i2c_device_probe,    .remove     = i2c_device_remove,    .shutdown   = i2c_device_shutdown,    .pm     = &i2c_device_pm_ops,};

具体代码如下

/*drivers/I2C/i2c-core.c*/static int i2c_device_match(struct device *dev, struct device_driver *drv){    struct i2c_client   *client = i2c_verify_client(dev);    struct i2c_driver   *driver;    if (!client)        return 0;    /* Attempt an OF style match */    if (of_driver_match_device(dev, drv))        return 1;    driver = to_i2c_driver(drv);    /* match on an id table if there is one */    if (driver->id_table)        return i2c_match_id(driver->id_table, client) != NULL;    return 0;}

通过i2c_match_id函数进行最后的匹配

/*drivers/I2C/i2c-core.c*/static const struct i2c_device_id *i2c_match_id(const struct i2c_device_id *id,                        const struct i2c_client *client){    while (id->name[0]) {        if (strcmp(client->name, id->name) == 0)            return id;        id++;    }    return NULL;}

主要匹配设备的名字。到此就设备和驱动就匹配上了。