问题：pcf8563 RTC设备驱动不能被正常的加载！问题分析过程。问题在下午得到解决，虽然解决的办法比较笨，采用的是不断的使用printk来跟踪rtc-8563驱动的加载的过程，以及iic模块的工作过程。曾经想过将内核的DEBUG打开，打开的方法在/linux2.6.21/include/linux/device.h文件中搜索DEBUG，这样的话，设备的所有的操作的debug信息都会输出，你会受不了，因为输出的无用的信息会掩盖你需要的真正的信息。所以就改为在i2c-core.c和rtc-8563文件中加入printk调试信息来跟踪系统的信息输出。我们来分析一下rtc驱动的加载过程。Linux驱动的i2c文件夹下有algos，busses，chips三个文件夹，另外还有i2c-core.c和i2c-dev.c两个文件。其中 i2c-core.c文件实现了I2C core框架，是Linux内核用来维护和管理的I2C的核心部分，其中维护了两个静态的List，分别记录系统中的I2C driver结构和I2C adapter结构。I2C core提供接口函数，允许一个I2C adatper，I2C driver和I2C client初始化时在I2C core中进行注册，以及退出时进行注销。同时还提供了I2C总线读写访问的一般接口，主要应用在I2C设备驱动中。在rtc-8563文件中：static int __init pcf8563_init(void){    return i2c_add_driver(&pcf8563_driver);}static void __exit pcf8563_exit(void){    i2c_del_driver(&pcf8563_driver);}MODULE_AUTHOR("Alessandro Zummo <a.zummo@towertech.it>");MODULE_DESCRIPTION("Philips PCF8563/Epson RTC8564 RTC driver");MODULE_LICENSE("GPL");MODULE_VERSION(DRV_VERSION);module_init(pcf8563_init);module_exit(pcf8563_exit);从这里我们可以知道模块加载的初始化函数和卸载函数都是使用的i2c的框架函数i2c_add_driver和i2c_del_driver。i2c_add_driver被定义在 include/linux/i2c.h文件中。其实质是i2c-core.c文件中的i2c_register_driver函数该函数的原型如下：int i2c_register_driver(struct module *owner, struct i2c_driver *driver){    struct list_head   *item;    struct i2c_adapter *adapter;    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;    res = driver_register(&driver->driver);    if (res)        return res;    mutex_lock(&core_lists);    //将该driver的list成员加入到全局的drivers链表尾部，linux中大量存在这种链表的结构体    list_add_tail(&driver->list,&drivers);    pr_debug("i2c-core: driver [%s] registered\n", driver->driver.name);    /* now look for instances of driver on our adapters */    if (driver->attach_adapter) {//该函数搜索整个adapters链表，item指向每一个链表中的成员，这里实际是一个for循环。//      #define list_for_each(pos, head) //        for (pos = (head)->next; prefetch(pos->next), pos //!=(head); pos = pos->next)        list_for_each(item,&adapters) {  //获得一个适配器结构体            adapter = list_entry(item, struct i2c_adapter, list);            driver->attach_adapter(adapter);        }    }    mutex_unlock(&core_lists);    return 0;}EXPORT_SYMBOL(i2c_register_driver);在这个函数中，首先向内核中注册你的驱动，然后锁信号量。。最关键的一步是：driver->attach_adapter(adapter);而attach_adapter就是在rtc-pcf8563.c文件中定义的重要的驱动结构体，定义如下。static struct i2c_driver pcf8563_driver = {    .driver        = {        .name    = "pcf8563",    },    .id        = I2C_DRIVERID_PCF8563,    .attach_adapter = &pcf8563_attach,    .detach_client    = &pcf8563_detach,};所以也就是说i2c框架函数会回调你写的适配器加载函数，我们的适配器加载函数是pcf8563_attach函数。该函数定义如下：static int pcf8563_attach(struct i2c_adapter *adapter){    return i2c_probe(adapter, &addr_data, pcf8563_probe);}调用i2c框架函数i2c_probe来进行适配器的加载。在下面这个函数中传递参数为适配器变量：adapter。i2c_client_address_data结构体原型static struct i2c_client_address_data addr_data =http://www.mamicode.com/ {                .normal_i2c    = normal_i2c,                        .probe        = probe,                        .ignore        = ignore,                        .forces        = forces,                    }注意，在我们的rtc-8563.c文件中只定义了normal_i2c数组。static unsigned short normal_i2c[] = { 0x51,I2C_CLIENT_END };而出错的地方就在这里，原来的定义没有0x51这个成员，所以根本不去加载pcf8563这个器件。int i2c_probe(struct i2c_adapter *adapter,          struct i2c_client_address_data *address_data,          int (*found_proc) (struct i2c_adapter *, int, int)){    int i, err;    int adap_id = i2c_adapter_id(adapter);    /* Force entries are done first, and are not affected by ignore       entries *///为空，不执行    if (address_data->forces) {        unsigned short **forces = address_data->forces;        int kind;        for (kind = 0; forces[kind]; kind++) {            for (i = 0; forces[kind][i] != I2C_CLIENT_END;                 i += 2) {                if (forces[kind][i] == adap_id                 || forces[kind][i] == ANY_I2C_BUS) {                    dev_dbg(&adapter->dev, "found force "                        "parameter for adapter %d, "                        "addr 0x%02x, kind %d\n",                        adap_id, forces[kind][i + 1],                        kind);                    err = i2c_probe_address(adapter,                        forces[kind][i + 1],                        kind, found_proc);                    if (err)                        return err;                }            }        }    }    /* Stop here if we can‘t use SMBUS_QUICK */    if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_QUICK)) {        if (address_data->probe[0] == I2C_CLIENT_END         && address_data->normal_i2c[0] == I2C_CLIENT_END)            return 0;        dev_warn(&adapter->dev, "SMBus Quick command not supported, "             "can‘t probe for chips\n");        return -1;    }    /* Probe entries are done second, and are not affected by ignore       entries either */    for (i = 0; address_data->probe[i] != I2C_CLIENT_END; i += 2) {        if (address_data->probe[i] == adap_id         || address_data->probe[i] == ANY_I2C_BUS) {            dev_dbg(&adapter->dev, "found probe parameter for "                "adapter %d, addr 0x%02x\n", adap_id,                address_data->probe[i + 1]);            err = i2c_probe_address(adapter,                        address_data->probe[i + 1],                        -1, found_proc);            if (err)                return err;        }    }    /* Normal entries are done last, unless shadowed by an ignore entry *///执行这部！通过i2c_probe_address函数来回调你编写的pcf8563_probe加载函数。    for (i = 0; address_data->normal_i2c[i] != I2C_CLIENT_END; i += 1) {        int j, ignore;        ignore = 0;        for (j = 0; address_data->ignore[j] != I2C_CLIENT_END;             j += 2) {            if ((address_data->ignore[j] == adap_id ||                 address_data->ignore[j] == ANY_I2C_BUS)             && address_data->ignore[j + 1]                == address_data->normal_i2c[i]) {                dev_printk(KERN_ERR ,&adapter->dev, "found ignore "                    "parameter for adapter %d, "                    "addr 0x%02x\n", adap_id,                    address_data->ignore[j + 1]);                ignore = 1;                break;            }        }        if (ignore)            continue;        dev_dbg(&adapter->dev, "found normal entry for adapter %d, "            "addr 0x%02x\n", adap_id,            address_data->normal_i2c[i]);        err = i2c_probe_address(adapter, address_data->normal_i2c[i],                    -1, found_proc);        if (err)            return err;    }    return 0;}i2c_probe_address的原型存在于i2c-core.c文件中：static int i2c_probe_address(struct i2c_adapter *adapter, int addr, int kind,                 int (*found_proc) (struct i2c_adapter *, int, int)){    int err;    /* Make sure the address is valid */    if (addr < 0x03 || addr > 0x77) {        dev_warn(&adapter->dev, "Invalid probe address 0x%02x\n",             addr);        return -EINVAL;    }    /* Skip if already in use */    if (i2c_check_addr(adapter, addr))        return 0;    /* Make sure there is something at this address, unless forced */    if (kind < 0) {        if (i2c_smbus_xfer(adapter, addr, 0, 0, 0,                   I2C_SMBUS_QUICK, NULL) < 0)            return 0;        /* prevent 24RF08 corruption */        if ((addr & ~0x0f) == 0x50)            i2c_smbus_xfer(adapter, addr, 0, 0, 0,                       I2C_SMBUS_QUICK, NULL);    }    /* Finally call the custom detection function *///这里回调你写的适配器加载函数pcf8563_probe，完成一个iic适配器的加载    err = found_proc(adapter, addr, kind);    /* -ENODEV can be returned if there is a chip at the given address       but it isn‘t supported by this chip driver. We catch it here as       this isn‘t an error. */    if (err == -ENODEV)        err = 0;    if (err)        dev_warn(&adapter->dev, "Client creation failed at 0x%x (%d)\n",             addr, err);    return err;}