【Linux驱动开发】I2C
Linux内核将I2C驱动分成两部分
- I2C总线驱动：SOC的I2C控制器驱动，也称为I2C适配器驱动。半导体厂商编写。
- I2C设备驱动：具体I2C设备的驱动。SOC使用者编写。
I2C总线驱动
Linux内核将SOC的I2C适配器抽象为i2c_adapter，include/linux/i2c.h。
struct i2c_adapter {
struct module *owner;
unsigned int class; /* classes to allow probing for */
const struct i2c_algorithm *algo; /* the algorithm to access the bus */
void *algo_data;
/* data fields that are valid for all devices */
struct rt_mutex bus_lock;
int timeout; /* in jiffies */
int retries;
struct device dev; /* the adapter device */
int nr;
char name[48];
struct completion dev_released;
struct mutex userspace_clients_lock;
struct list_head userspace_clients;
struct i2c_bus_recovery_info *bus_recovery_info;
const struct i2c_adapter_quirks *quirks;
};- i2c_algorithm类型的指针变量algo，是I2C适配器与I2C设备通信的方法，include/linux/i2c.h。
struct i2c_algorithm {
/* If an adapter algorithm can't do I2C-level access, set master_xfer
to NULL. If an adapter algorithm can do SMBus access, set
smbus_xfer. If set to NULL, the SMBus protocol is simulated
using common I2C messages */
/* master_xfer should return the number of messages successfully
processed, or a negative value on error */
int (*master_xfer)(struct i2c_adapter *adap, struct i2c_msg *msgs,
int num);
int (*smbus_xfer) (struct i2c_adapter *adap, u16 addr,
unsigned short flags, char read_write,
u8 command, int size, union i2c_smbus_data *data);
/* To determine what the adapter supports */
u32 (*functionality) (struct i2c_adapter *);
#if IS_ENABLED(CONFIG_I2C_SLAVE)
int (*reg_slave)(struct i2c_client *client);
int (*unreg_slave)(struct i2c_client *client);
#endif
};- master_xfer：I2C适配器传输函数，与I2C设备进行通信。
- smbus_xfer：SMBUS总线的传输函数。
I2C总线驱动首先初始化i2c_adapter结构体变量，然后设置i2c_algorithm中的master_xfer函数，最后通过i2c_add_adapter或i2c_add_numbered_adapter函数向Linux系统注册。
int i2c_add_adapter(struct i2c_adapter *adapter);
int i2c_add_numbered_adapter(struct i2c_adapter *adap);- adapter/adap：要注册的I2C适配器。
- 返回值：0，成功；负值，失败。
使用i2c_del_adapter删除I2C适配器。
void i2c_del_adapter(struct i2c_adapter *adap);- adap：要删除的I2C适配器。
- 返回值：无。
I2C设备驱动
Linux定义i2c_client结构体描述设备信息，include/linux/i2c.h。
/**
* 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.
*/
struct i2c_client {
unsigned short flags; /* 标志 */
unsigned short addr; /* 芯片地址，低7位 */
char name[I2C_NAME_SIZE]; /* 名字*/
struct i2c_adapter *adapter;/* I2C适配器 */
struct device dev; /* 设备结构体 */
int irq; /* 设备中断 */
struct list_head detected; /* 成员列表 */
#if IS_ENABLED(CONFIG_I2C_SLAVE)
i2c_slave_cb_t slave_cb; /* 回调 */
#endif
};一个设备对应一个i2c_client，每检测到一个I2C设备就给这个I2C设备分配一个i2c_client。
Linux定义i2c_driver结构体描述驱动信息，include/linux/i2c.h。
/**
* 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").
*/
void (*alert)(struct i2c_client *, 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;
};- probe和remove函数在I2C设备匹配成功和关闭驱动后执行。
- device_driver：驱动结构体，使用设备树时需要设置of_match_table成员变量。
- id_table：未使用设备树的匹配列表。
i2c_driver初始化完成后，使用i2c_register_driver向Linux内核注册。
int i2c_register_driver(struct module *owner,
struct i2c_driver *driver);- owner：THIS_MODULE。
- driver：要注册的i2c_driver。
- 返回值：0，成功；负值，失败。
也可使用宏i2c_add_driver注册，对i2c_register_driver进行封装，只有一个driver参数。
#define i2c_add_driver(driver) i2c_register_driver(THIS_MODULE, driver)使用i2c_del_driver注销I2C设备驱动。
void i2c_del_driver(struct i2c_driver *driver);- driver：要注销的i2c_driver。
- 返回值：无。
i2c_driver注册流程
static int xxx_probe(struct i2c_client *client,
const struct i2c_device_id *id)
{
/* ... */
return 0;
}
static int xxx_remove(struct i2c_client *client)
{
/* ... */
return 0;
}
/* 无设备树匹配ID列表 */
static const struct i2c_device_id xxx_id[] = {
{"xxx", 0},
{}
};
/* 设备树匹配列表 */
static const struct of_device_id xxx_of_match[] = {
{.compatible = "xxx"},
{}
};
/* I2C驱动结构体 */
static struct i2c_driver xxx_driver = {
.probe = xxx_probe,
.remove = xxx_remove,
.driver = {
.owner = THIS_MODULE,
.name = "xxx",
.of_match_table = xxx_of_match,
},
.id_table = xxx_id,
};
/* 驱动入口函数 */
static int __init xxx_init(void)
{
int ret = 0;
ret = i2c_add_driver(&xxx_driver);
return ret;
}
/* 驱动出口函数 */
static void __exit xxx_exit(void)
{
i2c_del_driver(&xxx_driver);
}
module_init(xxx_init);
module_exit(xxx_exit);
I2C设备信息描述
未使用设备树
在BSP里面使用i2c_board_info结构体描述一个具体的I2C设备。
/**
* struct i2c_board_info - template for device creation
* @type: chip type, to initialize i2c_client.name
* @flags: to initialize i2c_client.flags
* @addr: stored in i2c_client.addr
* @platform_data: stored in i2c_client.dev.platform_data
* @archdata: copied into i2c_client.dev.archdata
* @of_node: pointer to OpenFirmware device node
* @fwnode: device node supplied by the platform firmware
* @irq: stored in i2c_client.irq
*
* I2C doesn't actually support hardware probing, although controllers and
* devices may be able to use I2C_SMBUS_QUICK to tell whether or not there's
* a device at a given address. Drivers commonly need more information than
* that, such as chip type, configuration, associated IRQ, and so on.
*
* i2c_board_info is used to build tables of information listing I2C devices
* that are present. This information is used to grow the driver model tree.
* For mainboards this is done statically using i2c_register_board_info();
* bus numbers identify adapters that aren't yet available. For add-on boards,
* i2c_new_device() does this dynamically with the adapter already known.
*/
struct i2c_board_info {
char type[I2C_NAME_SIZE];
unsigned short flags;
unsigned short addr;
void *platform_data;
struct dev_archdata *archdata;
struct device_node *of_node;
struct fwnode_handle *fwnode;
int irq;
};- 两个必须设置的变量：type，I2C设备名字。addr，I2C器件地址。
例如：未使用设备树的OV2540的I2C设备信息描述，使用了I2C_BOARD_INFO宏。
/**
* I2C_BOARD_INFO - macro used to list an i2c device and its address
* @dev_type: identifies the device type
* @dev_addr: the device's address on the bus.
*
* This macro initializes essential fields of a struct i2c_board_info,
* declaring what has been provided on a particular board. Optional
* fields (such as associated irq, or device-specific platform_data)
* are provided using conventional syntax.
*/
#define I2C_BOARD_INFO(dev_type, dev_addr) \
.type = dev_type, .addr = (dev_addr)static struct i2c_board_info mx27_3ds_i2c_camera = {
I2C_BOARD_INFO("ov2640", 0x30);
};使用设备树
在设备树中创建对应I2C设备节点。
例如：在i2c1节点下创建mag3110磁力计节点和ap3216c三合一传感器，描述这个两个I2C设备信息。
&i2c1 {
clock-frequency = <100000>;
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_i2c1>;
status = "okay";
mag3110@0e {
compatible = "fsl,mag3110";
reg = <0x0e>;
position = <2>;
};
ap3216c@1e {
compatible = "ap3216c";
reg = <0x1e>;
};
};
&iomuxc {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_hog_1>;
imx6ul-evk {
pinctrl_i2c1: i2c1grp {
fsl,pins = <
MX6UL_PAD_UART4_TX_DATA__I2C1_SCL 0x4001b8b0
MX6UL_PAD_UART4_RX_DATA__I2C1_SDA 0x4001b8b0
>;
};
};
};- ap3216c@1e：ap3216c为子节点名字，1e为ap3216c的I2C器件地址。
- compatible属性：用于匹配驱动。
- reg属性：用于设置器件地址，此处为ap3216c的I2C器件地址。
I2C设备数据收发
使用i2c_transfer函数会调用I2C适配器中的i2c_algorithm里面的master_xfer函数。
int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)- adap：使用的I2C适配器，i2c_client保存对应的i2c_adapter。
- msgs：I2C要发送的一个或多个消息。
- num：msgs消息数量。
- 返回值：非负值，发送的msgs数量；负值，失败。
Linux内核定义i2c_msg结构体描述消息，include/uapi/linux/i2c.h。
/**
* struct i2c_msg - an I2C transaction segment beginning with START
* @addr: Slave address, either seven or ten bits. When this is a ten
* bit address, I2C_M_TEN must be set in @flags and the adapter
* must support I2C_FUNC_10BIT_ADDR.
* @flags: I2C_M_RD is handled by all adapters. No other flags may be
* provided unless the adapter exported the relevant I2C_FUNC_*
* flags through i2c_check_functionality().
* @len: Number of data bytes in @buf being read from or written to the
* I2C slave address. For read transactions where I2C_M_RECV_LEN
* is set, the caller guarantees that this buffer can hold up to
* 32 bytes in addition to the initial length byte sent by the
* slave (plus, if used, the SMBus PEC); and this value will be
* incremented by the number of block data bytes received.
* @buf: The buffer into which data is read, or from which it's written.
*/
struct i2c_msg {
__u16 addr; /* slave address */
__u16 flags;
#define I2C_M_TEN 0x0010 /* this is a ten bit chip address */
#define I2C_M_RD 0x0001 /* read data, from slave to master */
#define I2C_M_STOP 0x8000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_NOSTART 0x4000 /* if I2C_FUNC_NOSTART */
#define I2C_M_REV_DIR_ADDR 0x2000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_IGNORE_NAK 0x1000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_NO_RD_ACK 0x0800 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_RECV_LEN 0x0400 /* length will be first received byte */
__u16 len; /* msg length */
__u8 *buf; /* pointer to msg data */
};- addr：从机地址。
- flags：标志。
- len：消息长度
- buf：消息数据。
I2C数据收发
struct xxx_dev{
void *private_data; /* 私有数据 */
};
/* 读取I2C设备多个寄存器数据
* dev：I2C设备；reg：读取的寄存器地址；val：读取的数据；len：读取数据长度
*/
static int xxx_read_regs(struct xxx_dev *dev, u8 reg, void *val, int len)
{
int ret;
struct i2c_msg msg[2];
struct i2c_client *client = (struct i2c_client *)dev->private_data;
/* msg[0] 第一条写消息，发送要读取的寄存器首地址 */
msg[0].addr = client->addr; /* I2C器件地址 */
msg[0].flags = 0; /* 标记为发送数据 */
msg[0].buf = ® /* 读取的首地址 */
msg[0].len = 1; /* reg长度 */
/* msg[1] 第二条读消息，读取寄存器数据 */
msg[1].addr = client->addr; /* I2C器件地址 */
msg[1].flags = I2C_M_RD; /* 标记为读取数据 */
msg[1].buf = val; /* 读取数据缓冲区 */
msg[1].len = len; /* 要读取的数据长度*/
ret = i2c_transfer(client->adapter, msg, 2);
if(ret == 2) {
ret = 0;
} else {
ret = -EREMOTEIO;
}
return ret;
}
/* 向I2C设备多个寄存器写入数据
* dev：I2C设备；reg：写入的寄存器地址；val：写入的数据；len：写入的数据长度
*/
static int xxx_write_regs(struct xxx_dev *dev, u8 reg, u8 *buf, u8 len)
{
u8 b[256];
struct i2c_msg msg;
struct i2c_client *client = (struct i2c_client *)dev->private_data;
b[0] = reg; /* 寄存器首地址 */
memcpy(&b[1], buf, len); /* 发送的数据拷贝数组b中 */
msg.addr = client->addr; /* I2C器件地址 */
msg.flags = 0; /* 标记为写数据 */
msg.buf = b; /* 要发送的数据缓冲区 */
msg.len = len + 1; /* 要发送的数据长度 */
return i2c_transfer(client->adapter, &msg, 1);
}
API函数-发送数据i2c_master_send
int i2c_master_send(const struct i2c_client *client,
const char *buf,
int count);- client：i2c_client。
- buf：要发送的数据。
- count：要发送的数据字节数，小于64KB。
- 返回值：非负值，发送的字节数；负值，失败。
API函数-接收数据i2c_master_recv
int i2c_master_recv(const struct i2c_client *client,
char *buf,
int count)- client：i2c_client。
- buf：要接收的数据。
- count：要接收的数据字节数，小于64KB。
- 返回值：非负值，接收的字节数；负值，失败。