Linux I2C驱动分析.docx

1、Linux I2C驱动分析一:前言I2c是philips提出的外设总线.I2C只有两条线,一条串行数据线:SDA,一条是时钟线SCL.正因为这样,它方便了工程人员的布线.另外,I2C是一种多主机控制总线.它和USB总线不同,USB是基于master-slave机制,任何设备的通信必须由主机发起才可以.而I2C是基于multi master机制.一同总线上可允许多个master.关于I2C协议的知识,这里不再赘述.可自行下载spec阅读即可. 二:I2C架构概述在linux中,I2C驱动架构如下所示: 如上图所示,每一条I2C对应一个adapter.在kernel中,每一个adapter提供了一

2、个描述的结构(struct i2c_adapter),也定义了adapter支持的操作(struct i2c_adapter).再通过i2c core层将i2c设备与i2c adapter关联起来.这个图只是提供了一个大概的框架.在下面的代码分析中,从下至上的来分析这个框架图.以下的代码分析是基于linux 2.6.26.分析的代码基本位于: linux-2.6.26.3/drivers/i2c/位置. 三:adapter注册在kernel中提供了两个adapter注册接口,分别为i2c_add_adapter()和i2c_add_numbered_adapter().由于在系统中可能存在多个

3、adapter,因为将每一条I2C总线对应一个编号,下文中称为I2C总线号.这个总线号的PCI中的总线号不同.它和硬件无关,只是软件上便于区分而已.对于i2c_add_adapter()而言,它使用的是动态总线号,即由系统给其分析一个总线号,而i2c_add_numbered_adapter()则是自己指定总线号,如果这个总线号非法或者是被占用,就会注册失败.分别来看一下这两个函数的代码:int i2c_add_adapter(struct i2c_adapter *adapter) int id, res = 0; retry: if (idr_pre_get(&i2c_adapter_id

4、r, 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 nr = id; return i2c_register_adapter(adapter);在这里涉及到一个idr结构.idr结构本来是为了配合pa

5、ge cache中的radix tree而设计的.在这里我们只需要知道,它是一种高效的搜索树,且这个树预先存放了一些内存.避免在内存不够的时候出现问题.所在,在往idr中插入结构的时候,首先要调用idr_pre_get()为它预留足够的空闲内存,然后再调用idr_get_new_above()将结构插入idr中,该函数以参数的形式返回一个id.以后凭这个id就可以在idr中找到相对应的结构了.对这个数据结构操作不太理解的可以查阅本站中有关radix tree的分析.注意一下idr_get_new_above(&i2c_adapter_idr, adapter,_i2c_first_dynami

6、c_bus_num, &id)的参数的含义,它是将adapter结构插入到i2c_adapter_idr中,存放位置的id必须要大于或者等于_i2c_first_dynamic_bus_num,然后将对应的id号存放在adapter-nr中.调用i2c_register_adapter(adapter)对这个adapter进行进一步注册. 看一下另外一人注册函数: i2c_add_numbered_adapter( ),如下所示:int i2c_add_numbered_adapter(struct i2c_adapter *adap) int id; int status; if (adap

7、-nr & MAX_ID_MASK) return -EINVAL; retry: if (idr_pre_get(&i2c_adapter_idr, GFP_KERNEL) = 0) return -ENOMEM; mutex_lock(&core_lock); /* above here means above or equal to, sigh; * we need the equal to result to force the result */ status = idr_get_new_above(&i2c_adapter_idr, adap, adap-nr, &id); if

8、(status = 0 & id != adap-nr) status = -EBUSY; idr_remove(&i2c_adapter_idr, id); mutex_unlock(&core_lock); if (status = -EAGAIN) goto retry; if (status = 0) status = i2c_register_adapter(adap); return status;对比一下就知道差别了,在这里它已经指定好了adapter-nr了.如果分配的id不和指定的相等,便返回错误. 过一步跟踪i2c_register_adapter().代码如下:stati

9、c int i2c_register_adapter(struct i2c_adapter *adap) int res = 0, dummy; mutex_init(&adap-bus_lock); mutex_init(&adap-clist_lock); INIT_LIST_HEAD(&adap-clients); mutex_lock(&core_lock); /* Add the adapter to the driver core. * If the parent pointer is not set up, * we add this adapter to the host bu

10、s. */ if (adap-dev.parent = NULL) adap-dev.parent = &platform_bus; pr_debug(I2C adapter driver %s forgot to specify physical devicen, adap-name); sprintf(adap-dev.bus_id, i2c-%d, adap-nr); adap-dev.release = &i2c_adapter_dev_release; adap-dev.class = &i2c_adapter_class; res = device_register(&adap-d

11、ev); if (res) goto out_list; dev_dbg(&adap-dev, adapter %s registeredn, adap-name); /* create pre-declared device nodes for new-style drivers */ if (adap-nr nr); goto out_unlock;首先对adapter和adapter中内嵌的struct device结构进行必须的初始化.之后将adapter内嵌的struct device注册.在这里注意一下adapter-dev的初始化.它的类别为i2c_adapter_class,如

12、果没有父结点,则将其父结点设为platform_bus.adapter-dev的名字为i2c + 总线号.测试一下:ericmochow i2c$ cd /sys/class/i2c-adapter/ericmochow i2c-adapter$ lsi2c-0可以看到,在我的PC上,有一个I2C adapter,看下详细信息:ericmochow i2c-adapter$ tree.- i2c-0 |- device - ./././devices/pci0000:00/0000:00:1f.3/i2c-0 |- name |- subsystem - ./././class/i2c-ada

13、pter - uevent3 directories, 2 files可以看到,该adapter是一个PCI设备.继续往下看:之后,在注释中看到,有两种类型的driver,一种是new-style drivers,另外一种是legacy driversNew-style drivers是在2.6近版的kernel加入的.它们最主要的区别是在adapter和i2c driver的匹配上. 3.1: new-style 形式的adapter注册对于第一种,也就是new-style drivers,将相关代码再次列出如下: if (adap-nr nr 小于_i2c_first_dynamic_bu

14、s_num的话,就会进入到i2c_scan_static_board_info().结合我们之前分析的adapter的两种注册分式: i2c_add_adapter()所分得的总线号肯会不会小于_i2c_first_dynamic_bus_num.只有i2c_add_numbered_adapter()才有可能满足:(adap-nr = _i2c_first_dynamic_bus_num) _i2c_first_dynamic_bus_num = busnum + 1; for (status = 0; len; len-, info+) struct i2c_devinfo *devinf

15、o; devinfo = kzalloc(sizeof(*devinfo), GFP_KERNEL); if (!devinfo) pr_debug(i2c-core: cant register boardinfo!n); status = -ENOMEM; break; devinfo-busnum = busnum; devinfo-board_info = *info; list_add_tail(&devinfo-list, &_i2c_board_list); mutex_unlock(&_i2c_board_lock); return status;这个函数比较简单, struc

16、t i2c_board_info用来表示I2C设备的一些情况,比如所在的总线.名称,地址,中断号等.最后,这些信息会被存放到_i2c_board_list链表. 跟踪i2c_scan_static_board_info():代码如下:static void i2c_scan_static_board_info(struct i2c_adapter *adapter) struct i2c_devinfo *devinfo; mutex_lock(&_i2c_board_lock); list_for_each_entry(devinfo, &_i2c_board_list, list) if

17、(devinfo-busnum = adapter-nr & !i2c_new_device(adapter, &devinfo-board_info) printk(KERN_ERR i2c-core: cant create i2c%d-%04xn, i2c_adapter_id(adapter), devinfo-board_info.addr); mutex_unlock(&_i2c_board_lock);该函数遍历挂在_i2c_board_list链表上面的i2c设备的信息,也就是我们在启动的时候指出的i2c设备的信息.如果指定设备是位于adapter所在的I2C总线上,那么,就调

18、用i2c_new_device().代码如下:struct i2c_client *i2c_new_device(struct i2c_adapter *adap, struct i2c_board_info const *info) struct i2c_client *client; int status; client = kzalloc(sizeof *client, GFP_KERNEL); if (!client) return NULL; client-adapter = adap; client-dev.platform_data = info-platform_data; d

19、evice_init_wakeup(&client-dev, info-flags & I2C_CLIENT_WAKE); client-flags = info-flags & I2C_CLIENT_WAKE; client-addr = info-addr; client-irq = info-irq; strlcpy(client-name, info-type, sizeof(client-name); /* a new style driver may be bound to this device when we * return from this function, or an

20、y later moment (e.g. maybe * hotplugging will load the driver module). and the device * refcount model is the standard driver model one. */ status = i2c_attach_client(client); if (status adapter指向了它所在的adapter.特别的,clinet-name为info-name.也是指定好了的.一切初始化完成之后,便会调用i2c_attach_client( ).看这个函数的字面意思,是将clinet关联起

21、来.到底怎么样关联呢?继续往下看:int i2c_attach_client(struct i2c_client *client) struct i2c_adapter *adapter = client-adapter; int res = 0; /初始化client内嵌的dev结构 /父结点为所在的adapter,所在bus为i2c_bus_type client-dev.parent = &client-adapter-dev; client-dev.bus = &i2c_bus_type; /如果client已经指定了driver,将driver和内嵌的dev关联起来 if (clie

22、nt-driver) client-dev.driver = &client-driver-driver; /指定了driver, 但不是newstyle的 if (client-driver & !is_newstyle_driver(client-driver) client-dev.release = i2c_client_release; client-dev.uevent_suppress = 1; else client-dev.release = i2c_client_dev_release; /clinet-dev的名称 snprintf(&client-dev.bus_id0

23、, sizeof(client-dev.bus_id), %d-%04x, i2c_adapter_id(adapter), client-addr); /将内嵌的dev注册 res = device_register(&client-dev); if (res) goto out_err; /将clinet链到adapter-clients中 mutex_lock(&adapter-clist_lock); list_add_tail(&client-list, &adapter-clients); mutex_unlock(&adapter-clist_lock); dev_dbg(&ad

24、apter-dev, client %s registered with bus id %sn, client-name, client-dev.bus_id); /如果adapter-cleinet_reqister存在,就调用它 if (adapter-client_register) if (adapter-client_register(client) dev_dbg(&adapter-dev, client_register failed for client %s at 0x%02xn, client-name, client-addr); return 0; out_err: d

25、ev_err(&adapter-dev, Failed to attach i2c client %s at 0x%02x (%d)n, client-name, client-addr, res); return res; 参考上面添加的注释,应该很容易理解这段代码了,就不加详细分析了.这个函数的名字不是i2c_attach_client()么?怎么没看到它的关系过程呢?这是因为:在代码中设置了client-dev所在的bus为i2c_bus_type .以为只需要有bus为i2c_bus_type的driver注册,就会产生probe了.这个过程呆后面分析i2c driver的时候再来详细

26、分析.3.2: legacy形式的adapter注册Legacy形式的adapter注册代码片段如下: dummy = bus_for_each_drv(&i2c_bus_type, NULL, adap, i2c_do_add_adapter); 这段代码遍历挂在i2c_bus_type上的驱动,然后对每一个驱动和adapter调用i2c_do_add_adapter().代码如下:static int i2c_do_add_adapter(struct device_driver *d, void *data) struct i2c_driver *driver = to_i2c_driver(d); struct i2c_adapter *adap = data; if (driver-attach_adapter) /* We ignore the return code; if it fails, too bad */ driver-attach_adapter(adap); return 0; 该函数很简单,就是调用driver的attach_adapter(