Linux2.6.25平台下的I2C驱动架构分析.doc

Linux2.6.25平台下的I2C驱动架构分析【摘要】本文以PowerPC+Linux 2.6.25 平台为例，详细分析了I2C总线的驱动架构。首先介绍了I2C的总体架构，从用户的角度将其分为三个层面，不同的开发者只需要关注相应的层面即可。然后分析了主要数据结构及其之间的相互关系，接着分析了不同层的具体实现，最后以一款EEPEOM为例讲述了如何在用户空间访问I2C驱动。对于ARM + Linux平台，只有平台依赖层即总线适配器驱动有差异。【关键字】PowerPC, I2C, i2c-core, adapter , i2c_algorithm, RTC, EEPROM目录1 I2C概述 32 I2C总体架构 32.1 硬件抽象层 32.2 平台依赖层 32.3 用户接口层 33 主要的数据结构 43.1 Adapter 43.2 I2c_algorithm 53.3 i2c_driver 53.4 Client 64 平台依赖层-总线适配器驱动 74.1 platform device 74.2 platform driver 94.3 Adapter及algorithm 125 硬件抽象层-I2C core 135.1 总线初始化 135.2 Adapter注册 155.3 驱动注册 165.4 数据传输 176 用户接口层-I2C设备驱动 186.1 统一的设备模型 186.1.1 关键数据结构 186.1.2 初始化 196.1.3 Open及release 216.1.4 数据收发 226.2 特定的设备驱动 266.2.1 关键数据结构 266.2.2 初始化 276.2.3 数据收发 297 驱动访问示例 297.1.1 写操作 297.1.2 读操作 318 参考鸣谢 33 1 I2C概述I2C只有两条线，一条串行数据线：SDA，一条是时钟线SCL。I2C是一种多主机控制总线，同一总线上可允许多个master，即总线上的设备都有主动发起数据传输的可能，依靠线与逻辑来实现无损仲裁。但通常情况是总线上有个带CPU的master，其他设备被master访问。2 I2C总体架构在2.6的Linux内核中，I2C的驱动架构分为如下三个层次：硬件抽象层、平台依赖层和用户接口层。2.1 硬件抽象层i2c-core.h和i2c-core.c为其主体框架代码，提供了核心数据结构的定义、i2c适配器驱动和设备驱动的注册、注销管理等API。其为硬件平台无关层，向下屏蔽了物理总线适配器的差异，定义了统一的访问策略和接口；其向上提供了统一的接口，以便I2C设备驱动通过总线适配器进行数据收发。2.2 平台依赖层i2c总线适配器（adapter）就是一条i2c总线的控制器（所谓控制是相对于本CPU来说的），在物理上连接若干i2c设备。在Linux驱动中，每种处理器平台有自己的适配器驱动，属于平台移植相关层。每一个特定的硬件平台在i2c/busses/目录下都有一个adapter的实现，对于PowerPC平台来说，其是i2c-mpc.c。其按照核心层定义的接口实现了i2c_adapter，提供了具体的访问方式i2c_algorithm。2.3 用户接口层设备驱动层为用户接口层，其为用户提供了通过I2C总线访问具体设备的接口。 3 主要的数据结构3.1 AdapterAdapter是对某一条I2C总线的抽象，是特定总线的相关属性的集合。http:/lxr.linux.no/#linux+v2.6.25/include/linux/i2c.h#L312 312struct i2c_adapter 313 struct module *owner; 314 unsigned int id; 315 unsigned int class; 316 const struct i2c_algorithm *algo; /* the algorithm to access the bus */ 317 void *algo_data; 318 319 /* - administration stuff. */ 320 int (*client_register)(struct i2c_client *); 321 int (*client_unregister)(struct i2c_client *); 322 323 /* data fields that are valid for all devices */ 324 u8 level; /* nesting level for lockdep */ 325 struct mutex bus_lock; / 326 struct mutex clist_lock; 327 328 int timeout; 329 int retries; 330 struct device dev; /* the adapter device */ 331 332 int nr; /*该成员描述了总线号*/ 333 struct list_head clients; /* i2c_client结构链表，该结构包含device，driver和 adapter结构*/ 334 char name48; 335 struct completion dev_released; 336; Algo是和底层硬件的接口，标识了具体的物理总线传输的实现。Clients为使用该总线的client链表。Nr为该适配器也就是某条I2C总线占据的全局编号。bus_lock总线的互斥锁，防止总线冲突。3.2 I2c_algorithmhttp:/lxr.linux.no/#linux+v2.6.25/include/linux/i2c.h#L291291struct i2c_algorithm 292 /* If an adapter algorithm cant do I2C-level access, set master_xfer 293 to NULL. If an adapter algorithm can do SMBus access, set 294 smbus_xfer. If set to NULL, the SMBus protocol is simulated 295 using common I2C messages */ 296 /* master_xfer should return the number of messages successfully 297 processed, or a negative value on error */ 298 int (*master_xfer)(struct i2c_adapter *adap,struct i2c_msg *msgs, 299 int num); 300 int (*smbus_xfer) (struct i2c_adapter *adap, u16 addr, 301 unsigned short flags, char read_write, 302 u8 command, int size, union i2c_smbus_data * data); 303 304 /* To determine what the adapter supports */ 305 u32 (*functionality) (struct i2c_adapter *); 306;主要就是master_xfer方法，其和具体的总线控制器相关，不同的CPU在实现上可能有差异。3.3 i2c_driverhttp:/lxr.linux.no/#linux+v2.6.25/include/linux/i2c.h#L105105struct i2c_driver 106 int id; 107 unsigned int class; 108 109 /* Notifies the driver that a new bus has appeared. This routine 110 * can be used by the driver to test if the bus meets its conditions 111 * & seek for the presence of the chip(s) it supports. If found, it 112 * registers the client(s) that are on the bus to the i2c admin. via 113 * i2c_attach_client. (LEGACY I2C DRIVERS ONLY) 114 */ 115 int (*attach_adapter)(struct i2c_adapter *); 116 int (*detach_adapter)(struct i2c_adapter *); 117 118 /* tells the driver that a client is about to be deleted & gives it 119 * the chance to remove its private data. Also, if the client struct 120 * has been dynamically allocated by the driver in the function above, 121 * it must be freed here. (LEGACY I2C DRIVERS ONLY) 122 */ 123 int (*detach_client)(struct i2c_client *); 124 125 /* Standard driver model interfaces, for new style i2c drivers. 126 * With the driver model, device enumeration is NEVER done by drivers; 127 * its done by infrastructure. (NEW STYLE DRIVERS ONLY) 128 */ 129 int (*probe)(struct i2c_client *); 130 int (*remove)(struct i2c_client *); 131 132 /* driver model interfaces that dont relate to enumeration */ 133 void (*shutdown)(struct i2c_client *); 134 int (*suspend)(struct i2c_client *, pm_message_t mesg); 135 int (*resume)(struct i2c_client *); 136 137 /* a ioctl like command that can be used to perform specific functions 138 * with the device. 139 */ 140 int (*command)(struct i2c_client *client,unsigned int cmd, void *arg); 141 142 struct device_driver driver; 143;Driver是为device服务的，i2c_driver注册时会扫描i2c bus上的设备，进行驱动和设备的绑定。主要有两种接口attach_adapter和probe，二者分别针对旧的和新式的驱动。3.4 Clienthttp:/lxr.linux.no/#linux+v2.6.25/include/linux/i2c.h#L168168struct i2c_client 169 unsigned short flags; /* div., see below */ 170 unsigned short addr; /* chip address - NOTE: 7bit */ 171 /* addresses are stored in the */ 172 /* _LOWER_ 7 bits */ 173 char nameI2C_NAME_SIZE; 174 struct i2c_adapter *adapter; /* the adapter we sit on */ 175 struct i2c_driver *driver; /* and our access routines */ 176 struct device dev; /* the device structure */ 177 int irq; /* irq issued by device (or -1) */ 178 char driver_nameKOBJ_NAME_LEN; 179 struct list_head list; /* DEPRECATED */ 180 struct completion released; 181;通常来说i2c_client对应着I2C总线上某个特定的slave或者是user space的某个用户对应，而此时的slave可以动态变化。4 平台依赖层-总线适配器驱动总线适配器驱动，本质上就是实现了具体的总线传输算法并向核心层注册了适配器。主要分为三个层面，platform device，platform driver及与I2C core的接口层。Linux内核的所有适配器驱动程序都在driver/i2c/busses/目录下， MPC8xxx驱动是i2c-mpc.c。4.1 platform device2.6内核中硬件资源的注册都采用了platform device的机制。对于PowerPC来说，其硬件资源是通过DTS来描述的。i2c3000 #address-cells = ; #size-cells = ; cell-index = ; compatible = fsl-i2c; reg = ; interrupts = ; interrupt-parent = ; dfsrr;i2c3100 #address-cells = ; #size-cells = ; cell-index = ; compatible = fsl-i2c; reg = ; interrupts = ; interrupt-parent = ; dfsrr; rtc51 /legacy I2C device，静态定义 device_type = rtc; compatible = Philips,8563; /设备类型 reg = ; /I2C地址 ;中断号及寄存器的基地址等信息会在设备树中描述了，此后只需利用platform_get_resource等标准接口自动获取即可，实现了驱动和资源的分离。cell-index标识了总线编号，也就是adapter的编号。随后在系统启动阶段会解析DTB文件，将相关资源注册到Platform bus上。http:/lxr.linux.no/#linux+v2.6.25/arch/powerpc/sysdev/fsl_soc.c#L454458static int _init fsl_i2c_of_init(void) 501 of_register_i2c_devices(np, i+); 429static void _init of_register_i2c_devices(struct device_node *adap_node, 430 int bus_num) 431 432 struct device_node *node = NULL; 433 434 while (node = of_get_next_child(adap_node, node) 435 struct i2c_board_info info = ; 436 const u32 *addr; 437 int len; 438 439 addr = of_get_property(node, reg, &len); 440 if (!addr | len (1 10) - 1) 441 printk(KERN_WARNING fsl_soc.c: invalid i2c device entryn); 442 continue; 443 444 445 info.irq = irq_of_parse_and_map(node, 0); 446 if (info.irq = NO_IRQ) 447 info.irq = -1; 448 449 if (of_find_i2c_driver(node, &info) 0) 450 continue; 451 452 info.addr = *addr; 453 454 i2c_register_board_info(bus_num, &info, 1); 455 456 397static struct i2c_driver_device i2c_devices _initdata = 398 ricoh,rs5c372a, rtc-rs5c372, rs5c372a, 399 ricoh,rs5c372b, rtc-rs5c372, rs5c372b, 400 ricoh,rv5c386, rtc-rs5c372, rv5c386, 401 ricoh,rv5c387a, rtc-rs5c372, rv5c387a, 402 dallas,ds1307, rtc-ds1307, ds1307, 403 dallas,ds1337, rtc-ds1307, ds1337, 404 dallas,ds1338, rtc-ds1307, ds1338, 405 dallas,ds1339, rtc-ds1307, ds1339, 406 dallas,ds1340, rtc-ds1307, ds1340, 407 stm,m41t00, rtc-ds1307, m41t00, 408 dallas,ds1374, rtc-ds1374, rtc-ds1374, 409; 410在i2c_devices列表里描述了那些采用传统的I2C驱动的设备列表。同时DTS文件中也需要描述，二者会利用of_find_i2c_driver进行匹配。 411static int _init of_find_i2c_driver(struct device_node *node, 412 struct i2c_board_info *info) 413 414 int i; 415 416 for (i = 0; i driver_name, i2c_devicesi.i2c_driver, 420 KOBJ_NAME_LEN) = KOBJ_NAME_LEN | 421 strlcpy(info-type, i2c_devicesi.i2c_type, 422 I2C_NAME_SIZE) = I2C_NAME_SIZE) 423 return -ENOMEM; 424 return 0; 425 426 return -ENODEV; 4274.2 platform driver394 395/* Structure for a device driver */ 396static struct platform_driver fsl_i2c_driver = 397 .probe = fsl_i2c_probe, 398 .remove = fsl_i2c_remove, 399 .driver = 400 .owner = THIS_MODULE, 401 .name = fsl-i2c, /匹配因子 402 , 403; 404 405static int _init fsl_i2c_init(void) 406 407 return platform_driver_register(&fsl_i2c_driver); 408 409 410static void _exit fsl_i2c_exit(void) 411 412 platform_driver_unregister(&fsl_i2c_driver); 413 414 415module_init(fsl_i2c_init); 416module_exit(fsl_i2c_exit);fsl_i2c_driver注册时会扫描platform bus上的所有设备，匹配因子是fsl-i2c，匹配成功后调用fsl_i2c_probe将设备和驱动绑定起来，具体过程参加详解Linux2.6内核中基于platform机制的驱动模型，随后向系统注册一个adapter。/sailor_8318/archive/2010/01/29/5267698.aspx318static int fsl_i2c_probe(struct platform_device *pdev) 319 320 int result = 0; 321 struct mpc_i2c *i2c; 322 struct fsl_i2c_platform_data *pdata; 323 struct resource *r = platform_get_resource(pdev, IORESOURCE_MEM, 0); 324 325 pdata = (struct fsl_i2c_platform_data *) pdev-dev.platform_data; 326 327 i2c = kzalloc(sizeof(*i2c), GFP_KERNEL); 328 if (!i2c) 329 return -ENOMEM; 330 331 i2c-irq = platform_get_irq(pdev, 0); 332 if (i2c-irq flags = pdata-device_flags; 337 init_waitqueue_head(&i2c-queue); 338 339 i2c-base = ioremap(phys_addr_t)r-start, MPC_I2C_REGION); 340 341 if (!i2c-base) 342 printk(KERN_ERR i2c-mpc - failed to map controllern); 343 result = -ENOMEM; 344 goto fail_map; 345 346 347 if (i2c-irq != 0) 348 if (result = request_irq(i2c-irq, mpc_i2c_isr, 349 IRQF_SHARED, i2c-mpc, i2c) adap = mpc_ops; 359 i2c-adap.nr = pdev-id; 360 i2c_set_adapdata(&i2c-adap, i2c); 361 i2c-adap.dev.parent = &pdev-dev; 362 if (result = i2c_add_numbered_adapter(&i2c-adap) irq != 0) 371 free_irq(i2c-irq, i2c); 372 fail_irq: 373 iounmap(i2c-base); 374 fail_map: 375 fail_get_irq: 376 kfree(i2c); 377 return result; 378; 379 380static int fsl_i2c_remove(struct platform_device *pdev) 381 382 struct mpc_i2c *i2c = platform_get_drvdata(pdev); 383 384 i2c_del_adapter(&i2c-adap); 385 platform_set_drvdata(pdev, NULL); 386 387 if (i2c-irq != 0) 388 free_irq(i2c-irq, i2c); 389 390 iounmap(i2c-base); 391 kfree(i2c); 392 return 0; 393;pdev-id为platform data中的devid，为I2C的总线编号，其在设备树文件中描述。PowerPC的adapter驱动使用了i2c_add_numbered_adapter()注册，总线号最初保存在 platform_data中。4.3 Adapter及algorithm这一层主要是定义了关键的数据结构adapter和algorithm。http:/lxr.linux.no/#linux+v2.6.25/drivers/i2c/busses/i2c-mpc.c#L309309static struct i2c_adapter mpc_ops = 310 .owner = THIS_MODULE, 311 .name = MPC adapter, 312 .id = I2C_HW_MPC107, 313 .algo = &mpc_algo, 314 .class = I2C_CLASS_HWMON, 315 .timeout = 1, 316;304static const struct i2c_algorithm mpc_algo = 305 .master_xfer = mpc_xfer, 306 .functionality = mpc_functionality, 307; 308http:/lxr.linux.no/#linux+v2.6.25/drivers/i2c/busses/i2c-mpc.c#L256256static int mpc_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num) 257 258 struct i2c_msg *pmsg; 259 int i; 260 int ret = 0; 261 unsigned long orig_jiffies = jiffies; 262 struct mpc_i2c *i2c = i2c_get_adapdata(adap); 263 264 mpc_i2c_start(i2c); 265 266 /* Allow bus up to 1s to become not busy */ /一定程度上避免总线冲突，收发数据前先查询总线状态 267 while (readb(i2c-base + MPC_I2C_SR) & CSR_MBB) 268 if (signal_pending(current) 269 p