RTC设备驱动

时间：2010-04-07 来源：cao5170

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 <[email protected]>");
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 = {            \
    .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;
}