I2C子系统

Linux的总线基本都遵循分层分离原则。

I2C子系统体系结构

可以看到I2C子系统也是分层分离。

在STM32的I2C驱动中，一般要编写两部分代码，一部分是STM32的I2C控制器代码，一部分跟具体芯片相关的代码。 跟I2C控制器驱动的代码一旦写好，后续使用就不用修改

Linux中的I2C驱动也是这样做的，抽象出了两部分 ： I2C适配器驱动 和 I2C设备驱动

I2C适配器驱动是跟芯片控制器相关的驱动，一般是由芯片厂商实现添加进linux内核源码中。

而一般工程师要实现的就是I2C设备驱动

核心数据结构

include\linux\i2c.h

structi2c_adapter {structmodule *owner;unsignedintclass;/* classes to allow probing for */conststructi2c_algorithm *algo;/* the algorithm to access the bus */void *algo_data;/* data fields that are valid for all devices    */conststructi2c_lock_operations *lock_ops;structrt_mutexbus_lock;structrt_mutexmux_lock;int timeout;            /* in jiffies */int retries;structdevicedev;/* the adapter device */int nr;char name[48];structcompletiondev_released;structmutexuserspace_clients_lock;structlist_headuserspace_clients;structi2c_bus_recovery_info *bus_recovery_info;conststructi2c_adapter_quirks *quirks;structirq_domain *host_notify_domain;};#define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)

• linux中使用struct i2c_adapter描述I2C适配器驱动
• 对应一个I2C适配器驱动需要向外收发数据的能力，跟数据收发相关的成员 ：适配器算法 struct i2c_algorithm *algo

这是imx6ull的I2C适配器驱动实现：drivers\i2c\busses\i2c-imx.c

staticstructplatform_driveri2c_imx_driver = {    .probe = i2c_imx_probe,    .remove = i2c_imx_remove,    .driver = {        .name = DRIVER_NAME,        .pm = I2C_IMX_PM_OPS,        .of_match_table = i2c_imx_dt_ids,    },    .id_table = imx_i2c_devtype,};staticint __init i2c_adap_imx_init(void){return platform_driver_register(&i2c_imx_driver);}subsys_initcall(i2c_adap_imx_init);staticvoid __exit i2c_adap_imx_exit(void){    platform_driver_unregister(&i2c_imx_driver);}module_exit(i2c_adap_imx_exit);

可以看到i2c适配器驱动也是使用platform总线实现的。

适配器算法：

structi2c_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,unsignedshort 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};

• I2C总线最终则是会调用master_xfer完成
• 类似的I2c的SMBUS总线在会调用smbus_xfer进行传输

I2C设备驱动则主要关注以下数据结构：

structi2c_client {unsignedshort flags;        /* div., see below        */unsignedshort addr;        /* chip address - NOTE: 7bit    *//* addresses are stored in the    *//* _LOWER_ 7 bits        */char name[I2C_NAME_SIZE];structi2c_adapter *adapter;/* the adapter we sit on    */structdevicedev;/* the device structure        */int irq;            /* irq issued by device        */structlist_headdetected;#if IS_ENABLED(CONFIG_I2C_SLAVE)i2c_slave_cb_t slave_cb;    /* callback for slave mode    */#endif};

• 使用struct i2c_client描述设备信息（硬件信息），类型platform平台总线的platform_device

structi2c_driver {unsignedintclass;/* Standard driver model interfaces */int (*probe)(struct i2c_client *, conststruct i2c_device_id *);int (*remove)(struct i2c_client *);/* New driver model interface to aid the seamless removal of the     * current probe()'s, more commonly unused than used second parameter.     */int (*probe_new)(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,unsignedint data);/* a ioctl like command that can be used to perform specific functions     * with the device.     */int (*command)(struct i2c_client *client, unsignedint cmd, void *arg);structdevice_driverdriver;conststructi2c_device_id *id_table;/* Device detection callback for automatic device creation */int (*detect)(struct i2c_client *, struct i2c_board_info *);constunsignedshort *address_list;structlist_headclients;bool disable_i2c_core_irq_mapping;};

• 使用struct i2c_driver来描述驱动，实现用户驱动重点关注该数据结构

注册/注销I2C驱动：

inti2c_add_driver(struct i2c_driver *driver)voidi2c_del_driver(struct i2c_driver *driver)

内核提供的I2C传输接口：

inti2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num){int ret;if (adap->algo->master_xfer) {#ifdef DEBUGfor (ret = 0; ret < num; ret++) {            dev_dbg(&adap->dev,"master_xfer[%d] %c, addr=0x%02x, len=%d%s\n",                ret, (msgs[ret].flags & I2C_M_RD) ? 'R' : 'W',                msgs[ret].addr, msgs[ret].len,                (msgs[ret].flags & I2C_M_RECV_LEN) ? "+" : "");        }#endifif (in_atomic() || irqs_disabled()) {            ret = i2c_trylock_bus(adap, I2C_LOCK_SEGMENT);if (!ret)/* I2C activity is ongoing. */return -EAGAIN;        } else {            i2c_lock_bus(adap, I2C_LOCK_SEGMENT);        }        ret = __i2c_transfer(adap, msgs, num);        i2c_unlock_bus(adap, I2C_LOCK_SEGMENT);return ret;    } else {        dev_dbg(&adap->dev, "I2C level transfers not supported\n");return -EOPNOTSUPP;    }}

• if (adap->algo->master_xfer)
   ，可以看到发送最终调用的就是适配器中算法成员的master_xfer函数i2c读写关键数据结构：

structi2c_msg {    __u16 addr;    /* slave address            */    __u16 flags;#define I2C_M_RD        0x0001    /* read data, from slave to master *//* I2C_M_RD is guaranteed to be 0x0001! */#define I2C_M_TEN        0x0010    /* this is a ten bit chip address */#define I2C_M_DMA_SAFE        0x0200    /* the buffer of this message is DMA safe *//* makes only sense in kernelspace *//* userspace buffers are copied anyway */#define I2C_M_RECV_LEN        0x0400    /* length will be first received byte */#define I2C_M_NO_RD_ACK        0x0800    /* if I2C_FUNC_PROTOCOL_MANGLING */#define I2C_M_IGNORE_NAK    0x1000    /* if I2C_FUNC_PROTOCOL_MANGLING */#define I2C_M_REV_DIR_ADDR    0x2000    /* if I2C_FUNC_PROTOCOL_MANGLING */#define I2C_M_NOSTART        0x4000    /* if I2C_FUNC_NOSTART */#define I2C_M_STOP        0x8000    /* if I2C_FUNC_PROTOCOL_MANGLING */    __u16 len;        /* msg length                */    __u8 *buf;        /* pointer to msg data            */};

注释很清楚解析了成员是干什么用的。

I2C读写模板：

staticintap3216c_i2c_write_reg(struct i2c_client *client, uint8_t reg_addr, uint8_t data){int ret = 0;#if 0    structi2c_msgmsgs[2];    msgs[0].addr = client->addr;        msgs[0].buf = ®_addr;           /* 发送寄存器地址 */    msgs[0].flags = 0;                  /* I2C方向 ：写数据 */    msgs[0].len = sizeof(reg_addr);    msgs[1].addr = client->addr;    msgs[1].buf = &data;                /* 写数据 */    msgs[1].flags = 0;                  /* I2C方向 ：写数据 */    msgs[1].len = sizeof(data);#elseuint8_t buf[2];structi2c_msgmsg;    buf[0] = reg_addr;    buf[1] = data;    msg.addr = client->addr;        msg.buf = buf;           /* 发送寄存器地址 */    msg.flags = 0;                  /* I2C方向 ：写数据 */    msg.len = 2;#endif    ret = i2c_transfer(client->adapter, &msg, 1);if (ret < 0)return ret;elseif (ret != 1)return -EIO;return0;}staticintap3216c_i2c_read_reg(struct i2c_client *client, uint8_t reg_addr, uint8_t *data){int ret = 0;structi2c_msgmsgs[2];    msgs[0].addr = client->addr;    msgs[0].buf = ®_addr;              /* 发送寄存器地址 */    msgs[0].flags = 0;                    /* I2C方向 ：写数据 */    msgs[0].len = sizeof(reg_addr);    msgs[1].addr = client->addr;    msgs[1].buf = data;                    /* 读取寄存器数据 */    msgs[1].flags = I2C_M_RD;              /* I2C方向 ：读数据 */    msgs[1].len = 1;    ret = i2c_transfer(client->adapter, msgs, 2);if (ret < 0)return ret;elseif (ret != 2)return -EIO;return0;}

imx6ull设备树中对I2C的描述

arch\arm\boot\dts\imx6ull.dtsi

适配器驱动描述：