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 - represent an I2C device driver * @class: What kind of i2c device we instantiate (for detect) * @attach_adapter: Callback for bus addition (deprecated) * @probe: Callback for device binding * @remove: Callback for device unbinding * @shutdown: Callback for device shutdown * @alert: Alert callback, for example for the SMBus alert protocol * @command: Callback for bus-wide signaling (optional) * @driver: Device driver model driver * @id_table: List of I2C devices supported by this driver * @detect: Callback for device detection * @address_list: The I2C addresses to probe (for detect) * @clients: List of detected clients we created (for i2c-core use only) * * The driver.owner field should be set to the module owner of this driver. * The driver.name field should be set to the name of this driver. * * For automatic device detection, both @detect and @address_list must * be defined. @class should also be set, otherwise only devices forced * with module parameters will be created. The detect function must * fill at least the name field of the i2c_board_info structure it is * handed upon successful detection, and possibly also the flags field. * * If @detect is missing, the driver will still work fine for enumerated * devices. Detected devices simply won't be supported. This is expected * for the many I2C/SMBus devices which can't be detected reliably, and * the ones which can always be enumerated in practice. * * The i2c_client structure which is handed to the @detect callback is * not a real i2c_client. It is initialized just enough so that you can * call i2c_smbus_read_byte_data and friends on it. Don't do anything * else with it. In particular, calling dev_dbg and friends on it is * not allowed. */struct i2c_driver { unsigned int class;
 /* 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);