Linux Kernel 设备驱动之I2C之client描述

前面我们已经了解到i2c的host描述，对于设备来说，其描述较为简单，数据结构实现如下：

/**
 * struct i2c_client - represent an I2C slave device
 * @flags: I2C_CLIENT_TEN indicates the device uses a ten bit chip address;
 * I2C_CLIENT_PEC indicates it uses SMBus Packet Error Checking
 * @addr: Address used on the I2C bus connected to the parent adapter.
 * @name: Indicates the type of the device, usually a chip name that's
 * generic enough to hide second-sourcing and compatible revisions.
 * @adapter: manages the bus segment hosting this I2C device
 * @dev: Driver model device node for the slave.
 * @irq: indicates the IRQ generated by this device (if any)
 * @detected: member of an i2c_driver.clients list or i2c-core's
 * userspace_devices list
 * @slave_cb: Callback when I2C slave mode of an adapter is used. The adapter
 * calls it to pass on slave events to the slave driver.
 *
 * An i2c_client identifies a single device (i.e. chip) connected to an
 * i2c bus. The behaviour exposed to Linux is defined by the driver
 * managing the device.
 */
struct i2c_client {
 unsigned short flags;  /* div., see below  */
 unsigned short addr;  /* chip address - NOTE: 7bit */
     /* addresses are stored in the */
     /* _LOWER_ 7 bits  */
 char name[I2C_NAME_SIZE];
 struct i2c_adapter *adapter; /* the adapter we sit on */
 struct device dev;  /* the device structure  */
 int irq;   /* irq issued by device  */
 struct list_head detected;
#if IS_ENABLED(CONFIG_I2C_SLAVE)
 i2c_slave_cb_t slave_cb; /* callback for slave mode */
#endif
};

显然，对于I2c设备来说，其最主要是提供的i2c地址，这里用addr描述。对于内核驱动模型来说，任何设备都需要内嵌

struct device dev，以能完全跟踪描述设备。

对于一个I2C设备来说，其驱动类型定义如下：

struct i2c_driver

/* Notifies the driver that a new bus has appeared. You should avoid
  * using this, it will be removed in a near future.
  */
 int (*attach_adapter)(struct i2c_adapter *) __deprecated;
 /* Standard driver model interfaces */
 int (*probe)(struct i2c_client *, const struct i2c_device_id *);
 int (*remove)(struct i2c_client *);
 /* driver model interfaces that don't relate to enumeration  */
 void (*shutdown)(struct i2c_client *);
 /* Alert callback, for example for the SMBus alert protocol.
  * The format and meaning of the data value depends on the protocol.
  * For the SMBus alert protocol, there is a single bit of data passed
  * as the alert response's low bit ("event flag").
  * For the SMBus Host Notify protocol, the data corresponds to the
  * 16-bit payload data reported by the slave device acting as master.
  */
 void (*alert)(struct i2c_client *, enum i2c_alert_protocol protocol,
        unsigned int data);
 /* a ioctl like command that can be used to perform specific functions
  * with the device.
  */
 int (*command)(struct i2c_client *client, unsigned int cmd, void *arg);
 struct device_driver driver;
 const struct i2c_device_id *id_table;
 /* Device detection callback for automatic device creation */
 int (*detect)(struct i2c_client *, struct i2c_board_info *);
 const unsigned short *address_list;
 struct list_head clients;
};
显然，设备驱动是完成对I2C设备的驱动。

需要注意里面struct device_driver driver的设置，其也是用于满足设备驱动模型要求。

需要注意，一般来说，i2c_client是静态定义或者DTS分析得到的一个内核对象，也就是说其是内核I2C框架层

分析得到的对象，一般不需要用户直接分配。而I2C设备的驱动则需要静态定义实现，并通过函数

i2c_register_driver()注册到I2C框架层，此函数对外提供i2c_add_driver().
#define i2c_add_driver(driver) \
 i2c_register_driver(THIS_MODULE, driver)


/*
 * An i2c_driver is used with one or more i2c_client (device) nodes to access
 * i2c slave chips, on a bus instance associated with some i2c_adapter.
 */
int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
{
 int res;
 /* Can't register until after driver model init */
 if (unlikely(WARN_ON(!i2c_bus_type.p)))
  return -EAGAIN;
 /* add the driver to the list of i2c drivers in the driver core */
 driver->driver.owner = owner;设备驱动
 driver->driver.bus = &i2c_bus_type;设备驱动所在总线类型
 /* When registration returns, the driver core
  * will have called probe() for all matching-but-unbound devices.
  */
 res = driver_register(&driver->driver);注册设备驱动，设备驱动模型要求
 if (res)
  return res;
 /* Drivers should switch to dev_pm_ops instead. */
 if (driver->suspend)
  pr_warn("i2c-core: driver [%s] using legacy suspend method\n",
   driver->driver.name);
 if (driver->resume)
  pr_warn("i2c-core: driver [%s] using legacy resume method\n",
   driver->driver.name);
 pr_debug("i2c-core: driver [%s] registered\n", driver->driver.name);
 INIT_LIST_HEAD(&driver->clients);
 /* Walk the adapters that are already present */
 i2c_for_each_dev(driver, __process_new_driver);驱动开始探测设备，如果有设备，则初始化它。
 return 0;
}

设备驱动定义形式如下：

static const struct i2c_device_id i2c_slave_eeprom_id[] = {
 { "slave-24c02", 2048 / 8 },
 { }
};
MODULE_DEVICE_TABLE(i2c, i2c_slave_eeprom_id);
static struct i2c_driver i2c_slave_eeprom_driver = {
 .driver = {
  .name = "i2c-slave-eeprom",
 },
 .probe = i2c_slave_eeprom_probe,
 .remove = i2c_slave_eeprom_remove,
 .id_table = i2c_slave_eeprom_id,
};
module_i2c_driver(i2c_slave_eeprom_driver);