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:
[cpp]
- 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:
[cpp]
- 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:
[cpp]
- 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:
[cpp]
- struct i2c_devinfo {
- struct list_head list; //连接指针指向前后设备
- int busnum; //所在bus的编号
- struct i2c_board_info board_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 {
- char type[I2C_NAME_SIZE]; //名字
- unsigned short flags; //标志
- unsigned short addr; //地址
- void *platform_data; //私有特殊数据
- struct dev_archdata *archdata;
- #ifdef CONFIG_OF
- struct device_node *of_node; //节点
- #endi
- int irq; //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:
[cpp]
- 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_COMPAT
- class_compat_unregister(i2c_adapter_compat_class);
- bus_err:
- #endif
- bus_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:
[cpp]
- 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
- else
- dev_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 DEBUG
- for (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) ? “+” : “”);
- }
- #endif
- if (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;
- int status;
- /*
- * 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_OF
- client->dev.of_node = info->of_node;
- #endif
- dev_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[cpp]
- int i2c_add_adapter(struct i2c_adapter *adapter)
- {
- int id, 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_COMPAT
- res = 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:
[cpp]
- 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。
[cpp]
- /************************************
- * 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:
[cpp]
- 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:
[cpp]
- 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adapter
- if (!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adapter
- snprintf(client->name, I2C_NAME_SIZE, “i2c-dev %d”, adap->nr);
- //指定driver,代表创建他的driver
- client->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client
- file->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:
[cpp]
- 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client
- struct i2c_client *client = file->private_data;
- //大小不能超过8192
- if (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 ^_^