linux设备模型之i2c子系统

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      I2c子系统将i2c控制器(i2c寄存器所在的那块电路)抽象出来，用adapter（适配器）这个结构来描述，可以说一个适配器就代表一条i2c总线，而挂接在i2c总线上的设备是用client这个结构体来表述，另外i2c_bus上的设备链表挂接的不单单是连接的这条i2c上的client，同样adapter也作为一个设备挂在其所在的i2c_bus，也就是说控制器和设备都作为i2c_bus上的设备连接在设备链表，他们用内嵌的device的type这个成员来区分，适配器的类型为i2c_adapter_type，client的类型为i2c_client_type。

一、i2c相关的描述结构

     首先看一下i2c子系统给adapter定义的描述结构：

struct i2c_adapter {struct module *owner;unsigned int id;unsigned int class； // 适配器支持的类型，如传感器，eeprom等const struct i2c_algorithm *algo; //该适配器的通信函数void *algo_data;/* data fields that are valid for all devices*/struct rt_mutex bus_lock;int timeout; //超时时间限定int retries; //通信重复次数限定/* * 内嵌的标准device，其中dev->type标识该设备 * 是个adapter，其值为i2c_adapter_type */struct device dev;int nr; //适配器编号也是bus编号，第几条i2c总线char name[48]; //名字struct completion dev_released;struct mutex userspace_clients_lock;struct list_head userspace_clients;};

   再来看一下client的描述结构：

struct i2c_client {unsigned short flags; //设备的标志，如唤醒标志等等/* chip address - NOTE: 7bit*//* addresses are stored in the*//* _LOWER_ 7 bits*/unsigned short addr; //设备的地址char name[I2C_NAME_SIZE]; //设备的名字struct i2c_adapter *adapter; //设备所属的适配器struct i2c_driver *driver; //设备的driver/* * 内嵌的标准device模型，其中dev->type标识该设备 * 是个client，其值为i2c_client_type */struct device dev;/* the device structure*/int irq; //中断号struct list_head detected; //挂接点，挂接在adapter};

    下面是driver的表述结构i2c_driver：

struct i2c_driver {unsigned int class; //支持的类型，与adapter的class相对/* Notifies the driver that a new bus has appeared or is about to be * removed. You should avoid using this if you can, it will probably * be removed in a near future. */ int (*attach_adapter)(struct i2c_adapter *); //旧式探测函数int (*detach_adapter)(struct i2c_adapter *);/* 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 *);int (*suspend)(struct i2c_client *, pm_message_t mesg);int (*resume)(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); /* * 内嵌的标准driver，driver的of_match_table成员也用于标识其支持 * 的设备，并且优先级高于id_table */struct device_driver driver;const struct i2c_device_id *id_table; //支持的client信息表/* Device detection callback for automatic device creation */int (*detect)(struct i2c_client *, struct i2c_board_info *); //探测函数const unsigned short *address_list; //driver支持的client地址struct list_head clients; //挂接其探测到的支持的设备};

      另外client端有一条全局链表，用于串联所有i2c的client设备，为__i2c_board_list，也就是说client可以静态注册亦可动态
被探测，静态注册挂接在该链表上的结构为：

struct i2c_devinfo {struct list_headlist; //连接指针指向前后设备intbusnum; //所在bus的编号struct i2c_board_infoboard_info; //板级平台信息相关的结构体};//其中 i2c_board_info结构的源码为： struct i2c_board_info {chartype[I2C_NAME_SIZE]; //名字unsigned shortflags; //标志unsigned shortaddr; //地址void*platform_data; //私有特殊数据struct dev_archdata*archdata;#ifdef CONFIG_OFstruct device_node *of_node; //节点#endiintirq; //中断号};

    i2c_devinfo结构静态注册的信息最后都会被整合集成到client中，形成一个标准的i2c_client设备并注册。

二、i2c核心初始化代码分析

    首先看一下i2c平台无关的核心初始化，代码位于drivers/i2c/i2c-core.c下：

static int __init i2c_init(void){int retval; /* * 注册i2c_bus */retval = bus_register(&i2c_bus_type); if (retval)return retval;#ifdef CONFIG_I2C_COMPAT /* * 在sys/class下创建适配器目录 */i2c_adapter_compat_class = class_compat_register("i2c-adapter");if (!i2c_adapter_compat_class) {retval = -ENOMEM;goto bus_err;}#endif /* * 增加一个虚拟的driver */retval = i2c_add_driver(&dummy_driver); if (retval)goto class_err;return 0;class_err:#ifdef CONFIG_I2C_COMPATclass_compat_unregister(i2c_adapter_compat_class); bus_err:#endifbus_unregister(&i2c_bus_type);return retval;}//其中的i2c_bus_type原型为：struct bus_type i2c_bus_type = {.name= "i2c",.match= i2c_device_match,.probe= i2c_device_probe,.remove= i2c_device_remove,.shutdown= i2c_device_shutdown,.pm= &i2c_device_pm_ops,};

三、i2c_add_driver分析

    驱动端的统一接口为i2c_add_driver：

static inline int i2c_add_driver(struct i2c_driver *driver){/* *注册i2c driver，可能是adapter的，也可能是client的 */return i2c_register_driver(THIS_MODULE, driver);}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 *//* * i2c_driver内嵌的标准driver赋值，其bus指定为i2c_bus_type */driver->driver.owner = owner;driver->driver.bus = &i2c_bus_type; /* When registration returns, the driver core * will have called probe() for all matching-but-unbound devices. */ /*注册标准的driver，driver注册后会去i2c_bus_type的设备链表上匹配 *设备，匹配函数用的是bus端的，也就是i2c_device_match，如果匹配成功 *将建立标准关联，并且将调用bus端的probe函数初始化这个设备，即 *函数i2c_device_probe，下面会逐个分析 */res = driver_register(&driver->driver);if (res)return res;pr_debug("i2c-core: driver [%s] registered/n", driver->driver.name); /* * 把该driver的clients初始化，该成员连接着这个driver可以操作的具 * 体设备 */INIT_LIST_HEAD(&driver->clients);/* Walk the adapters that are already present */mutex_lock(&core_lock); /* * 遍历挂接在该i2c设备链表上的设备，并对其都调用__process_new_driver * 函数 */bus_for_each_dev(&i2c_bus_type, NULL, driver, __process_new_driver);mutex_unlock(&core_lock);return 0;}/***************************** 匹配函数i2c_device_match *****************************/static int i2c_device_match(struct device *dev, struct device_driver *drv){/* * i2c_verify_client检查匹配的这个设备是否为i2c_client_type * 类型，如果不是则返回NULL，此处的匹配只是针对i2c设备的 * 不是适配器 */struct i2c_client*client = i2c_verify_client(dev);struct i2c_driver*driver; /* * 如果不是i2c设备类型就返回 */if (!client)return 0;/* Attempt an OF style match *//* * 如果定义了CONFIG_OF_DEVICE，那么就利用 * drv.of_match_table成员表进行匹配 */if (of_driver_match_device(dev, drv))return 1; /* * 由内嵌的driver得到外面封装的i2c_driver */driver = to_i2c_driver(drv);/* match on an id table if there is one *//* * 如果i2c_driver->id_table存在，也就是支持的设备信息表 * 存在，那么利用这个表进行匹配 */if (driver->id_table)return i2c_match_id(driver->id_table, client) != NULL;return 0;}/*********************************** 初始化设备函数i2c_device_probe ***********************************/static int i2c_device_probe(struct device *dev){/* * 检查如果设备类型不是client则返回 */struct i2c_client*client = i2c_verify_client(dev);struct i2c_driver*driver;int status;if (!client)return 0; /* * dev->driver指向匹配完成的driver，根据该标准 * driver得到其外围封装的i2c_driver */driver = to_i2c_driver(dev->driver);/* * 如果该i2c_driver的probe成员或者id_table成员为 * NULL则退出 */if (!driver->probe || !driver->id_table)return -ENODEV;/* * client的driver成员赋值为该i2c_driver */client->driver = driver;/* * 唤醒该设备 */if (!device_can_wakeup(&client->dev))device_init_wakeup(&client->dev,client->flags & I2C_CLIENT_WAKE);dev_dbg(dev, "probe/n"); /* * 利用i2c_driver的probe成员初始化该设备，此部分为实际平台相关 */status = driver->probe(client, i2c_match_id(driver->id_table, client));/* * 失败则清除client指定的driver */if (status) {client->driver = NULL;i2c_set_clientdata(client, NULL);}return status;}/************************************************************** 下面看一下当找到一个dev后调用的__process_new_driver函数 **************************************************************/static int __process_new_driver(struct device *dev, void *data){/* * 设备的类型如果不是i2c_adapter类型就推出 * 下面的代码是针对i2c适配器的代码 */if (dev->type != &i2c_adapter_type) return 0;/* * 如果这个设备代表i2c适配器，则调用i2c_do_add_adapter * 此时的data类型为i2c_driver */return i2c_do_add_adapter(data, to_i2c_adapter(dev));//根据设备得到他的适配器 //i2c_driver。第一个是i2c_driver}/************************** i2c_do_add_adapter函数 **************************/static int i2c_do_add_adapter(struct i2c_driver *driver, struct i2c_adapter *adap){/* Detect supported devices on that bus, and instantiate them *//* * 利用该适配器和该i2c_driver探测该适配器所在的这条i2c总线 * 找到该driver支持的设备并实例化它 */i2c_detect(adap, driver); /* Let legacy drivers scan this bus for matching devices *//* * 老版本的探测利用i2c_driver的attach_adapter函数 */if (driver->attach_adapter) {/* We ignore the return code; if it fails, too bad */driver->attach_adapter(adap);}return 0;}/***************************** 重点看一下i2c_detect函数 *****************************/static int i2c_detect(struct i2c_adapter *adapter, struct i2c_driver *driver){const unsigned short *address_list;struct i2c_client *temp_client;int i, err = 0;int adap_id = i2c_adapter_id(adapter); /* * 得到该i2c_driver指定的client地址范围 */address_list = driver->address_list; /* * driver平台相关的detect函数和client地址范围不能为NULL */if (!driver->detect || !address_list) return 0;/* Set up a temporary client to help detect callback */ /* * 申请一块client内存 */temp_client = kzalloc(sizeof(struct i2c_client), GFP_KERNEL);if (!temp_client)return -ENOMEM; /* * 申请的client结构的adapter成员设置为当前的adapter */temp_client->adapter = adapter; /* Stop here if the classes do not match *//* * 当前adapter的类型如果和driver的类型不一样，则退出 * 例如：适配器的类型可以为传感器，eeprom，driver类型必须 * 与其匹配 */if (!(adapter->class & driver->class)) goto exit_free; /* * 根据指定的支持的地址范围开始逐一探测 */for (i = 0; address_list[i] != I2C_CLIENT_END; i += 1) {dev_dbg(&adapter->dev, "found normal entry for adapter %d, ""addr 0x%02x/n", adap_id, address_list[i]); /* * 临时申请的client的地址设置为这次要探测的地址 */temp_client->addr = address_list[i];err = i2c_detect_address(temp_client, driver); if (err)goto exit_free;} exit_free:kfree(temp_client);return err;}/*********************************** 继续跟进i2c_detect_address函数 ***********************************/static int i2c_detect_address(struct i2c_client *temp_client, struct i2c_driver *driver){struct i2c_board_info info;struct i2c_adapter *adapter = temp_client->adapter;int addr = temp_client->addr;int err;/* Make sure the address is valid */ /* * 检查该地址是否有效，小于0x08或者大于0x77都是无效 * 地址，该函数在后面介绍 */err = i2c_check_addr_validity(addr);if (err) {dev_warn(&adapter->dev, "Invalid probe address 0x%02x/n", addr);return err;}/* Skip if already in use */ /* * 如果地址在使用中则跳过 */if (i2c_check_addr_busy(adapter, addr))return 0;/* Make sure there is something at this address */ /* * 默认初始化探测，确定该地址上有设备存在 */if (!i2c_default_probe(adapter, addr))return 0;/* Finally call the custom detection function */ /* * 走到这里将调用平台相关的自定义探测函数去探测该地址 * 上是否设备，并填充i2c_board_info结构体 */memset(&info, 0, sizeof(struct i2c_board_info));info.addr = addr;err = driver->detect(temp_client, &info);if (err) {/* -ENODEV is returned if the detection fails. We catch it here as this isn't an error. */return err == -ENODEV ? 0 : err;}/* Consistency check *//* * 填充的info名字为空，则结束否则实例化这个设备 */if (info.type[0] == '/0') {dev_err(&adapter->dev, "%s detection function provided ""no name for 0x%x/n", driver->driver.name,addr);} else {struct i2c_client *client;/* Detection succeeded, instantiate the device */dev_dbg(&adapter->dev, "Creating %s at 0x%02x/n",info.type, info.addr);/* * 根据当前适配器和填充的info实例化该地址上探测到的设备 */client = i2c_new_device(adapter, &info);/* * 实例化成功将该client挂到该driver的clients链表上 */if (client)list_add_tail(&client->detected, &driver->clients); //驱动挂到driver下elsedev_err(&adapter->dev, "Failed creating %s at 0x%02x/n",info.type, info.addr);}return 0;}/******************************* i2c_check_addr_validity函数 *******************************/static int i2c_check_addr_validity(unsigned short addr){/* * Reserved addresses per I2C specification: * 0x00 General call address / START byte * 0x01 CBUS address * 0x02 Reserved for different bus format * 0x03 Reserved for future purposes * 0x04-0x07 Hs-mode master code * 0x78-0x7b 10-bit slave addressing * 0x7c-0x7f Reserved for future purposes */if (addr < 0x08 || addr > 0x77)return -EINVAL;return 0;}/********************************** 再看一下i2c_default_probe函数 **********************************/static int i2c_default_probe(struct i2c_adapter *adap, unsigned short addr){int err;union i2c_smbus_data dummy;#ifdef CONFIG_X86 /* * 这里是对intel特殊设备的检查，就不深入看下去了 */if (addr == 0x73 && (adap->class & I2C_CLASS_HWMON) && i2c_check_functionality(adap, I2C_FUNC_SMBUS_READ_BYTE_DATA))err = i2c_smbus_xfer(adap, addr, 0, I2C_SMBUS_READ, 0, I2C_SMBUS_BYTE_DATA, &dummy);else#endif /* * 对特殊设备的检查 */if (!((addr & ~0x07) == 0x30 || (addr & ~0x0f) == 0x50) && i2c_check_functionality(adap, I2C_FUNC_SMBUS_QUICK))err = i2c_smbus_xfer(adap, addr, 0, I2C_SMBUS_WRITE, 0, I2C_SMBUS_QUICK, NULL); /* * i2c_check_functionality函数确定该i2c适配器所支持的通信方式 * 如果支持该方式则调用i2c_smbus_xfer函数 */else if (i2c_check_functionality(adap, I2C_FUNC_SMBUS_READ_BYTE))err = i2c_smbus_xfer(adap, addr, 0, I2C_SMBUS_READ, 0, I2C_SMBUS_BYTE, &dummy);else {dev_warn(&adap->dev, "No suitable probing method supported/n");err = -EOPNOTSUPP;}return err >= 0;}/******************************* i2c_check_functionality函数 *******************************/static inline int i2c_check_functionality(struct i2c_adapter *adap, u32 func){return (func & i2c_get_functionality(adap)) == func;}static inline u32 i2c_get_functionality(struct i2c_adapter *adap){ /* * 最终会调用adapter通信函数里面的functionality函数确定支持的 * 通信方式 */return adap->algo->functionality(adap);}/********************** i2c_smbus_xfer函数 **********************/s32 i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr, unsigned short flags, char read_write, u8 command, int protocol, union i2c_smbus_data *data){unsigned long orig_jiffies;int try;s32 res;flags &= I2C_M_TEN | I2C_CLIENT_PEC; /* * 如果适配器通信函数中的smbus_xfer函数存在，则直接利用它进行发送 */if (adapter->algo->smbus_xfer) {i2c_lock_adapter(adapter);/* Retry automatically on arbitration loss */orig_jiffies = jiffies;for (res = 0, try = 0; try <= adapter->retries; try++) {res = adapter->algo->smbus_xfer(adapter, addr, flags,read_write, command,protocol, data);if (res != -EAGAIN)break;if (time_after(jiffies, orig_jiffies + adapter->timeout))break;}i2c_unlock_adapter(adapter);} else /* * 否则利用i2c_smbus_xfer_emulated处理,此处也就是不支持smbus， * 则得利用i2c模拟smbus命令 */res = i2c_smbus_xfer_emulated(adapter, addr, flags, read_write, command, protocol, data);return res;}/******************************* i2c_smbus_xfer_emulated函数 *******************************/static s32 i2c_smbus_xfer_emulated(struct i2c_adapter *adapter, u16 addr, unsigned short flags, char read_write, u8 command, int size, union i2c_smbus_data *data){/* So we need to generate a series of msgs. In the case of writing, we need to use only one message; when reading, we need two. We initialize most things with sane defaults, to keep the code below somewhat simpler. */ /* * 为了进行通信我们必须创建msgs结构，当写时，我们需要一个这样的结构就 * 够了，当读的时候，我们需要两个 */unsigned char msgbuf0[I2C_SMBUS_BLOCK_MAX+3];unsigned char msgbuf1[I2C_SMBUS_BLOCK_MAX+2]; /* * 读的时候需要两次 */int num = read_write == I2C_SMBUS_READ ? 2 : 1; /* * 填充需要的两个msg结构 */struct i2c_msg msg[2] = { { addr, flags, 1, msgbuf0 }, { addr, flags | I2C_M_RD, 0, msgbuf1 } };int i;u8 partial_pec = 0;int status; /* * 将要发送的命令填充到msg0 */msgbuf0[0] = command;switch (size) { /* * 快速传输，多用于确定该地址有应答 */case I2C_SMBUS_QUICK:msg[0].len = 0;/* Special case: The read/write field is used as data */msg[0].flags = flags | (read_write == I2C_SMBUS_READ ?I2C_M_RD : 0);num = 1;break; /* * 字节传输，一次读写一个字节 */case I2C_SMBUS_BYTE:if (read_write == I2C_SMBUS_READ) {/* Special case: only a read! */msg[0].flags = I2C_M_RD | flags;num = 1;}break; /* * 命令+单字节形式传输 */case I2C_SMBUS_BYTE_DATA:if (read_write == I2C_SMBUS_READ)msg[1].len = 1;else {msg[0].len = 2;msgbuf0[1] = data->byte;}break; /* * 命令+字形式传输 */case I2C_SMBUS_WORD_DATA:if (read_write == I2C_SMBUS_READ)msg[1].len = 2;else {msg[0].len = 3;msgbuf0[1] = data->word & 0xff;msgbuf0[2] = data->word >> 8;}break; /* * 命令+字形式，需要应答 */case I2C_SMBUS_PROC_CALL:num = 2; /* Special case */read_write = I2C_SMBUS_READ;msg[0].len = 3;msg[1].len = 2;msgbuf0[1] = data->word & 0xff;msgbuf0[2] = data->word >> 8;break; /* * 多字节数据模式，字节数传输中不确定 */case I2C_SMBUS_BLOCK_DATA:if (read_write == I2C_SMBUS_READ) {msg[1].flags |= I2C_M_RECV_LEN;msg[1].len = 1; /* block length will be added by the underlying bus driver */} else {msg[0].len = data->block[0] + 2;if (msg[0].len > I2C_SMBUS_BLOCK_MAX + 2) {dev_err(&adapter->dev,"Invalid block write size %d/n",data->block[0]);return -EINVAL;}for (i = 1; i < msg[0].len; i++)msgbuf0[i] = data->block[i-1];}break; /* * 多字节数据传输，需要应答 */case I2C_SMBUS_BLOCK_PROC_CALL:num = 2; /* Another special case */read_write = I2C_SMBUS_READ;if (data->block[0] > I2C_SMBUS_BLOCK_MAX) {dev_err(&adapter->dev,"Invalid block write size %d/n",data->block[0]);return -EINVAL;}msg[0].len = data->block[0] + 2;for (i = 1; i < msg[0].len; i++)msgbuf0[i] = data->block[i-1];msg[1].flags |= I2C_M_RECV_LEN;msg[1].len = 1; /* block length will be added by the underlying bus driver */break; /* * 多字节数据传输，传输字节数确定 */case I2C_SMBUS_I2C_BLOCK_DATA:if (read_write == I2C_SMBUS_READ) {msg[1].len = data->block[0];} else {msg[0].len = data->block[0] + 1;if (msg[0].len > I2C_SMBUS_BLOCK_MAX + 1) {dev_err(&adapter->dev,"Invalid block write size %d/n",data->block[0]);return -EINVAL;}for (i = 1; i <= data->block[0]; i++)msgbuf0[i] = data->block[i];}break;default:dev_err(&adapter->dev, "Unsupported transaction %d/n", size);return -EOPNOTSUPP;}i = ((flags & I2C_CLIENT_PEC) && size != I2C_SMBUS_QUICK && size != I2C_SMBUS_I2C_BLOCK_DATA);if (i) {/* Compute PEC if first message is a write */if (!(msg[0].flags & I2C_M_RD)) {if (num == 1) /* Write only */i2c_smbus_add_pec(&msg[0]);else /* Write followed by read */partial_pec = i2c_smbus_msg_pec(0, &msg[0]);}/* Ask for PEC if last message is a read */if (msg[num-1].flags & I2C_M_RD)msg[num-1].len++;} /* * 调用i2c_transfer传输 */status = i2c_transfer(adapter, msg, num);if (status < 0)return status;/* Check PEC if last message is a read */if (i && (msg[num-1].flags & I2C_M_RD)) {status = i2c_smbus_check_pec(partial_pec, &msg[num-1]);if (status < 0)return status;} /* * 将得到的数据回传给data */if (read_write == I2C_SMBUS_READ)switch (size) {case I2C_SMBUS_BYTE:data->byte = msgbuf0[0];break;case I2C_SMBUS_BYTE_DATA:data->byte = msgbuf1[0];break;case I2C_SMBUS_WORD_DATA:case I2C_SMBUS_PROC_CALL:data->word = msgbuf1[0] | (msgbuf1[1] << 8);break;case I2C_SMBUS_I2C_BLOCK_DATA:for (i = 0; i < data->block[0]; i++)data->block[i+1] = msgbuf1[i];break;case I2C_SMBUS_BLOCK_DATA:case I2C_SMBUS_BLOCK_PROC_CALL:for (i = 0; i < msgbuf1[0] + 1; i++)data->block[i] = msgbuf1[i];break;}return 0;}/******************** i2c_transfer函数 ********************/int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num){unsigned long orig_jiffies;int ret, try;/* REVISIT the fault reporting model here is weak: * * - When we get an error after receiving N bytes from a slave, * there is no way to report "N". * * - When we get a NAK after transmitting N bytes to a slave, * there is no way to report "N" ... or to let the master * continue executing the rest of this combined message, if * that's the appropriate response. * * - When for example "num" is two and we successfully complete * the first message but get an error part way through the * second, it's unclear whether that should be reported as * one (discarding status on the second message) or errno * (discarding status on the first one). */ /* * 如果适配器的adap->algo->master_xfer函数存在，则调用它把 * 该信息发送出去 */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_adapter(adap);if (!ret)/* I2C activity is ongoing. */return -EAGAIN;} else {i2c_lock_adapter(adap);}/* Retry automatically on arbitration loss */orig_jiffies = jiffies;for (ret = 0, try = 0; try <= adap->retries; try++) {ret = adap->algo->master_xfer(adap, msgs, num);if (ret != -EAGAIN)break;if (time_after(jiffies, orig_jiffies + adap->timeout))break;}i2c_unlock_adapter(adap);return ret;} else {dev_dbg(&adap->dev, "I2C level transfers not supported/n");return -EOPNOTSUPP;}}/*********************************************** 回过头来看一下i2c_new_device这个实例化函数***********************************************/struct i2c_client *i2c_new_device(struct i2c_adapter *adap, struct i2c_board_info const *info){struct i2c_client*client;intstatus; /* * 为需要实例化的设备申请内存 */client = kzalloc(sizeof *client, GFP_KERNEL);if (!client)return NULL; /* * 指定适配器以及platform_data */client->adapter = adap;client->dev.platform_data = info->platform_data; /* * info->archdata存在将其赋值给client */if (info->archdata)client->dev.archdata = *info->archdata; /* * 标志、地址、中断号、名字 */client->flags = info->flags;client->addr = info->addr;client->irq = info->irq;strlcpy(client->name, info->type, sizeof(client->name));/* Check for address validity */ /* * 检查地址有效性 */status = i2c_check_client_addr_validity(client);if (status) {dev_err(&adap->dev, "Invalid %d-bit I2C address 0x%02hx/n",client->flags & I2C_CLIENT_TEN ? 10 : 7, client->addr);goto out_err_silent;}/* Check for address business */ /* * 检查地址是否被使用 */status = i2c_check_addr_busy(adap, client->addr);if (status)goto out_err; /* * 内嵌标准device的赋值 */client->dev.parent = &client->adapter->dev;client->dev.bus = &i2c_bus_type;client->dev.type = &i2c_client_type;#ifdef CONFIG_OFclient->dev.of_node = info->of_node;#endifdev_set_name(&client->dev, "%d-%04x", i2c_adapter_id(adap), client->addr); /* * 注册内嵌的标准device */status = device_register(&client->dev); if (status)goto out_err;dev_dbg(&adap->dev, "client [%s] registered with bus id %s/n",client->name, dev_name(&client->dev));return client;out_err:dev_err(&adap->dev, "Failed to register i2c client %s at 0x%02x ""(%d)/n", client->name, client->addr, status);out_err_silent:kfree(client);return NULL;}

     以上就是i2c通用driver添加的流程，下面看一下设备端，适配器的流程
四、i2c_add_adapter分析

int i2c_add_adapter(struct i2c_adapter *adapter){intid, res = 0;retry: /* * 得到bus号并将其插入搜索树，便于高效查找 * 此处不做深入分析 */if (idr_pre_get(&i2c_adapter_idr, GFP_KERNEL) == 0)return -ENOMEM;mutex_lock(&core_lock);/* "above" here means "above or equal to", sigh */res = idr_get_new_above(&i2c_adapter_idr, adapter,__i2c_first_dynamic_bus_num, &id);mutex_unlock(&core_lock);if (res < 0) {if (res == -EAGAIN)goto retry;return res;} /* * 适配器号赋值，代表i2c的编号 */adapter->nr = id;return i2c_register_adapter(adapter);}/************************************************ 来看一下适配器的注册函数i2c_register_adapter************************************************/static int i2c_register_adapter(struct i2c_adapter *adap){int res = 0;/* Can't register until after driver model init */ /* * bus私有属性结构不能为NULL */if (unlikely(WARN_ON(!i2c_bus_type.p))) {res = -EAGAIN;goto out_list;}rt_mutex_init(&adap->bus_lock);mutex_init(&adap->userspace_clients_lock);INIT_LIST_HEAD(&adap->userspace_clients);/* Set default timeout to 1 second if not already set */ /* * 超时时间设置为1s */if (adap->timeout == 0)adap->timeout = HZ; /* * 设置内嵌device的名字，指定bus，指定自身类型为适配器 */dev_set_name(&adap->dev, "i2c-%d", adap->nr);adap->dev.bus = &i2c_bus_type; adap->dev.type = &i2c_adapter_type; /* * 注册内嵌的标准device，此时将会出现在i2c_bus目录下 */res = device_register(&adap->dev); if (res)goto out_list;dev_dbg(&adap->dev, "adapter [%s] registered/n", adap->name);#ifdef CONFIG_I2C_COMPATres = class_compat_create_link(i2c_adapter_compat_class, &adap->dev, adap->dev.parent);if (res)dev_warn(&adap->dev, "Failed to create compatibility class link/n");#endif/* create pre-declared device nodes */ /* * client可以静态的添加，如果发现适配器号也就是i2c号 * 小于动态bus号，说明设备静态添加，则进行扫描 */if (adap->nr < __i2c_first_dynamic_bus_num)i2c_scan_static_board_info(adap); /* Notify drivers */mutex_lock(&core_lock); /* * 遍历bus的驱动端，对于每一个driver都调用__process_new_adapter */bus_for_each_drv(&i2c_bus_type, NULL, adap, __process_new_adapter);mutex_unlock(&core_lock);return 0;out_list:mutex_lock(&core_lock);idr_remove(&i2c_adapter_idr, adap->nr);mutex_unlock(&core_lock);return res;}/******************************************** 先来看一下i2c_scan_static_board_info函数********************************************/static void i2c_scan_static_board_info(struct i2c_adapter *adapter){struct i2c_devinfo*devinfo;down_read(&__i2c_board_lock); /* * 遍历全局的i2c的client链表，找到该适配器器所代表 * 总线上挂接的设备，用i2c_new_device实例化它， * i2c_new_device在前面已经分析过了，不在赘述 */list_for_each_entry(devinfo, &__i2c_board_list, list) {if (devinfo->busnum == adapter->nr&& !i2c_new_device(adapter,&devinfo->board_info))dev_err(&adapter->dev,"Can't create device at 0x%02x/n",devinfo->board_info.addr);}up_read(&__i2c_board_lock);}/*************************************** 再来看一下__process_new_adapter函数***************************************/static int __process_new_adapter(struct device_driver *d, void *data){ /* * 同样的归宿到了i2c_do_add_adapter下面，与前面分析的 * __process_new_driver相似，只是driver是针对适配器， * 而这次没有这个限制 */return i2c_do_add_adapter(to_i2c_driver(d), data);}

  依据以上的分析画出流程图如下:

 

      i2c_driver依据内部成员的设定，会走不同的分支，产生不同的作用，下面根据流程前后顺序总结一下：
当发现的是i2c_bus上的一个client时（发生在标准driver注册的匹配）：
 1、首先会进入到bus定义的匹配函数i2c_device_match如果定义了CONFIG_OF_DEVICE宏并且内部的标准
    driver结构定义了of_match_table成员，则利用其进行匹配；
 2、否则如果driver->id_table成员设定，则利用其进行匹配，否则匹配失败。
 3、如果匹配成功会调用i2c_bus的i2c_device_probe函数，该函数会判断，如果该i2c_driver的probe成员
    或者id_table成员为NULL，则返回，否则利用i2c_driver->probe初始化这个client。
当发现的是代表该i2c_bus的上的adapter时（发生在bus的遍历）:
 1、如果该driver的driver->detect或者address_list为NULL退出
 2、如果该adapter->class和driver->class不匹配也退出
 3、如果以上都成立最终会调用driver->detect函数，实例化支持的client
 4、如果driver->attach_adapter也被设定，含会走旧式的路线，直接利用driver->attach_adapter进行探测
      不过，一般不会让3&&4这种结果出现
  可见，i2c_driver的设置非常灵活，抓住关键成员就不难掌握其流程。

五、i2c关于dev下节点的产生及其操作

  该部分的代码位于rivers/i2c/i2c-dev.c下，我们从头看起：

 static int __init i2c_dev_init(void){int res;printk(KERN_INFO "i2c /dev entries driver/n"); /* * 注册名称为i2c主设备号为89的一个字符设备 */res = register_chrdev(I2C_MAJOR, "i2c", &i2cdev_fops);if (res)goto out; /* * 在class下产生i2c-dev节点，用于自动产生设备文件 */i2c_dev_class = class_create(THIS_MODULE, "i2c-dev");if (IS_ERR(i2c_dev_class)) {res = PTR_ERR(i2c_dev_class);goto out_unreg_chrdev;} /* * i2c_add_driver在上面已经分析过了 */res = i2c_add_driver(&i2cdev_driver);if (res)goto out_unreg_class;return 0;out_unreg_class:class_destroy(i2c_dev_class);out_unreg_chrdev:unregister_chrdev(I2C_MAJOR, "i2c");out:printk(KERN_ERR "%s: Driver Initialisation failed/n", __FILE__);return res;}//其中i2cdev_driver结构为：static struct i2c_driver i2cdev_driver = {.driver = {.name= "dev_driver",},.attach_adapter= i2cdev_attach_adapter,.detach_adapter= i2cdev_detach_adapter,};

     由于没有关于client的支持表的定义，因此匹配client时就会直接返回， 由于存在成员attach_adapter，因此当匹配adapter时会进入该函数。

/************************************* 来看一下i2cdev_attach_adapter函数*************************************/static int i2cdev_attach_adapter(struct i2c_adapter *adap){struct i2c_dev *i2c_dev;int res;i2c_dev = get_free_i2c_dev(adap);if (IS_ERR(i2c_dev))return PTR_ERR(i2c_dev);/* register this i2c device with the driver core *//* * 以上面注册的i2c_dev_class为父节点在目录class/i2c-dev下 * 产生i2c-0之类的节点，这样上层udev会根据该节点在dev目录下 * 自动创建对应的设备文件 */i2c_dev->dev = device_create(i2c_dev_class, &adap->dev, MKDEV(I2C_MAJOR, adap->nr), NULL, "i2c-%d", adap->nr);if (IS_ERR(i2c_dev->dev)) {res = PTR_ERR(i2c_dev->dev);goto error;} /* * 产生相关属性文件 */res = device_create_file(i2c_dev->dev, &dev_attr_name);if (res)goto error_destroy;pr_debug("i2c-dev: adapter [%s] registered as minor %d/n", adap->name, adap->nr);return 0;error_destroy:device_destroy(i2c_dev_class, MKDEV(I2C_MAJOR, adap->nr));error:return_i2c_dev(i2c_dev);return res;}

    通过以上分析可以看到i2c-dev层，找到一个adapter就会自动为其创建设备节点，形式类似于i2c-*,那么当应用层open对应的设备节点的时候，内核会自动调用刚才注册的字符设备的操作函数， 我们先来看一下刚才注册的字符设备的操作集：

static const struct file_operations i2cdev_fops = {.owner= THIS_MODULE,.llseek= no_llseek,.read= i2cdev_read,.write= i2cdev_write,.unlocked_ioctl= i2cdev_ioctl,.open= i2cdev_open,.release= i2cdev_release,};

    按照用户层的流程先看一下open函数i2cdev_open:

static int i2cdev_open(struct inode *inode, struct file *file){unsigned int minor = iminor(inode); //得到次设备号struct i2c_client *client;struct i2c_adapter *adap;struct i2c_dev *i2c_dev; /* * 次设备号其实是对应i2c总线号，下面函数遍历由次设备构成的链表 * i2c_dev_list，找到上面挂接的号码对应的i2c_dev结构 */i2c_dev = i2c_dev_get_by_minor(minor);if (!i2c_dev) //没找到，出错return -ENODEV;adap = i2c_get_adapter(i2c_dev->adap->nr); //得到绑定的adapterif (!adap)return -ENODEV;/* This creates an anonymous i2c_client, which may later be * pointed to some address using I2C_SLAVE or I2C_SLAVE_FORCE. * * This client is ** NEVER REGISTERED ** with the driver model * or I2C core code!! It just holds private copies of addressing * information and maybe a PEC flag. */client = kzalloc(sizeof(*client), GFP_KERNEL); //申请个client内存if (!client) {i2c_put_adapter(adap);return -ENOMEM;}//命名，依据adaptersnprintf(client->name, I2C_NAME_SIZE, "i2c-dev %d", adap->nr);//指定driver，代表创建他的driverclient->driver = &i2cdev_driver; //指定适配器client->adapter = adap;//通过file的私有成员传递创建的这个clientfile->private_data = client;return 0;}

      由open可见，我们要操作i2c下的设备，始终是需要通过adapter，物理上也是如此，操作设备都是通过控制器进行读写的，因此我们打开的始终是adapter而open过程中会创建client，来表述我们主观上是要操作设备。下面在看一下read函数：

static ssize_t i2cdev_read(struct file *file, char __user *buf, size_t count,loff_t *offset){char *tmp;int ret; //得到由open传递过来的创建的clientstruct i2c_client *client = file->private_data; //大小不能超过8192if (count > 8192)count = 8192; //申请count大小内存tmp = kmalloc(count, GFP_KERNEL);if (tmp == NULL)return -ENOMEM;pr_debug("i2c-dev: i2c-%d reading %zu bytes./n",iminor(file->f_path.dentry->d_inode), count); //调用i2c_master_recv进行进一步传送ret = i2c_master_recv(client, tmp, count);if (ret >= 0)//read的信息反馈给用户ret = copy_to_user(buf, tmp, count) ? -EFAULT : ret;kfree(tmp);return ret;}/***************************** 其中i2c_master_recv函数为*****************************/int i2c_master_recv(struct i2c_client *client, char *buf, int count){struct i2c_adapter *adap = client->adapter;struct i2c_msg msg;int ret; //利用msg组织信息结构msg.addr = client->addr;msg.flags = client->flags & I2C_M_TEN;msg.flags |= I2C_M_RD;msg.len = count;msg.buf = buf; //调用i2c_transfer发送ret = i2c_transfer(adap, &msg, 1);/* If everything went ok (i.e. 1 msg transmitted), return #bytes transmitted, else error code. */return (ret == 1) ? count : ret;}

    i2c_transfer函数上面已经分析过了，其会最终调用client所在adapter的adap->algo->master_xfer函数发送。

六、总结

    分析了linux下i2c子系统模型及其关键点，针对核心的平台无关代码进行了描述，以上为个人观点，如有不妥，还望指正 ^_^