【嵌入式Linux学习七步曲之第五篇 Linux内核及驱动编程】PowerPC + Linux2.6.25平台下的I2C驱动架构分析
PowerPC + Linux2.6.25平臺下的I2C驅動架構分析
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http://blog.csdn.net/sailor_8318/archive/2010/09/25/5905988.aspx
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【摘要】本文以PowerPC+Linux 2.6.25 平臺為例，詳細分析了I2C總線的驅動架構。首先介紹了I2C的總體架構，從用戶的角度將其分為三個層面，不同的開發者只需要關注相應的層面即可。然后分析了主要數據結構及其之間的相互關系，接著分析了不同層的具體實現，最后以一款EEPEOM為例講述了如何在用戶空間訪問I2C驅動。對于ARM + Linux平臺，只有平臺依賴層即總線適配器驅動有差異。
【關鍵字】PowerPC, I2C, i2c-core, adapter , i2c_algorithm, RTC, EEPROM
目錄
1??? I2C概述??? 3
2??? I2C總體架構??? 3
2.1??? 硬件抽象層??? 3
2.2??? 平臺依賴層??? 3
2.3??? 用戶接口層??? 3
3??? 主要的數據結構??? 4
3.1??? Adapter??? 4
3.2??? I2c_algorithm??? 5
3.3??? i2c_driver??? 5
3.4??? Client??? 6
4??? 平臺依賴層-總線適配器驅動??? 7
4.1??? platform device??? 7
4.2??? platform driver??? 9
4.3??? Adapter及algorithm??? 12
5??? 硬件抽象層-I2C core??? 13
5.1??? 總線初始化??? 13
5.2??? Adapter注冊??? 15
5.3??? 驅動注冊??? 16
5.4??? 數據傳輸??? 17
6??? 用戶接口層-I2C設備驅動??? 18
6.1??? 統一的設備模型??? 18
6.1.1??? 關鍵數據結構??? 18
6.1.2??? 初始化??? 19
6.1.3??? Open及release??? 21
6.1.4??? 數據收發??? 22
6.2??? 特定的設備驅動??? 26
6.2.1??? 關鍵數據結構??? 26
6.2.2??? 初始化??? 27
6.2.3??? 數據收發??? 29
7??? 驅動訪問示例??? 29
7.1.1??? 寫操作??? 29
7.1.2??? 讀操作??? 31
8??? 參考鳴謝??? 33
1??? I2C概述
I2C只有兩條線，一條串行數據線：SDA，一條是時鐘線SCL。I2C是一種多主機控制總線，同一總線上可允許多個master，即總線上的設備都有主動發起數據傳輸的可能，依靠線與邏輯來實現無損仲裁。但通常情況是總線上有個帶CPU的master，其他設備被master訪問。
2??? I2C總體架構
在2.6的Linux內核中，I2C的驅動架構分為如下三個層次：硬件抽象層、平臺依賴層和用戶接口層。
2.1??? 硬件抽象層
i2c-core.h和i2c-core.c為其主體框架代碼，提供了核心數據結構的定義、i2c適配器驅動和設備驅動的注冊、注銷管理等API。其為硬件平臺無關層，向下屏蔽了物理總線適配器的差異，定義了統一的訪問策略和接口；其向上提供了統一的接口，以便I2C設備驅動通過總線適配器進行數據收發。
2.2??? 平臺依賴層
i2c總線適配器（adapter）就是一條i2c總線的控制器（所謂控制是相對于本CPU來說的），在物理上連接若干i2c設備。在Linux驅動中，每種處理器平臺有自己的適配器驅動，屬于平臺移植相關層。每一個特定的硬件平臺在i2c/busses/目錄下都有一個adapter的實現，對于PowerPC平臺來說，其是i2c-mpc.c。其按照核心層定義的接口實現了i2c_adapter，提供了具體的訪問方式i2c_algorithm。
2.3??? 用戶接口層
設備驅動層為用戶接口層，其為用戶提供了通過I2C總線訪問具體設備的接口。
??????????????????????
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3??? 主要的數據結構
3.1??? Adapter
Adapter是對某一條I2C總線的抽象，是特定總線的相關屬性的集合。
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;? /*該成員描述了總線號*/??
?333??????? struct list_head clients;?????? /* i2c_client結構鏈表，該結構包含device，driver和 adapter結構*/??
?334??????? char name[48];
?335??????? struct completion dev_released;
?336};?
Algo是和底層硬件的接口，標識了具體的物理總線傳輸的實現。
Clients為使用該總線的client鏈表。
Nr為該適配器也就是某條I2C總線占據的全局編號。
bus_lock總線的互斥鎖，防止總線沖突。
3.2??? I2c_algorithm
http://lxr.linux.no/#linux+v2.6.25/include/linux/i2c.h#L291
291struct i2c_algorithm {
?292??????? /* If an adapter algorithm can't 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，其和具體的總線控制器相關，不同的CPU在實現上可能有差異。
3.3??? i2c_driver
http://lxr.linux.no/#linux+v2.6.25/include/linux/i2c.h#L105
105struct 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???????? * it's 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 don't 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是為device服務的，i2c_driver注冊時會掃描i2c bus上的設備，進行驅動和設備的綁定。主要有兩種接口attach_adapter和probe，二者分別針對舊的和新式的驅動。
3.4??? Client
http://lxr.linux.no/#linux+v2.6.25/include/linux/i2c.h#L168
168struct 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 name[I2C_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_name[KOBJ_NAME_LEN];
?179??????? struct list_head list;????????? /* DEPRECATED */
?180??????? struct completion released;
?181};
通常來說i2c_client對應著I2C總線上某個特定的slave或者是user space的某個用戶對應，而此時的slave可以動態變化。
4??? 平臺依賴層-總線適配器驅動
總線適配器驅動，本質上就是實現了具體的總線傳輸算法并向核心層注冊了適配器。主要分為三個層面，platform device，platform driver及與I2C core的接口層。
Linux內核的所有適配器驅動程序都在driver/i2c/busses/目錄下， MPC8xxx驅動是i2c-mpc.c。
4.1??? platform device
2.6內核中硬件資源的注冊都采用了platform device的機制。對于PowerPC來說，其硬件資源是通過DTS來描述的。
i2c@3000 {
??? #address-cells = <1>;
??? #size-cells = <0>;
??? cell-index = <0>;
??? compatible = "fsl-i2c";
??? reg = <0x3000 0x100>;
??? interrupts = <14 0x8>;
??? interrupt-parent = <&ipic>;
??? dfsrr;
};
i2c@3100 {
??? #address-cells = <1>;
??? #size-cells = <0>;
??? cell-index = <1>;
??? compatible = "fsl-i2c";
??? reg = <0x3100 0x100>;
??? interrupts = <15 0x8>;
??? interrupt-parent = <&ipic>;
??? dfsrr;
??? rtc@51 {? //legacy I2C device，靜態定義
??????????????????????? device_type = "rtc";
??????????????????????? compatible = "Philips,8563"; //設備類型
??????????????????????? reg = <0x51>;? //I2C地址
??????????????? };
};
中斷號及寄存器的基地址等信息會在設備樹中描述了，此后只需利用platform_get_resource等標準接口自動獲取即可，實現了驅動和資源的分離。cell-index標識了總線編號，也就是adapter的編號。
隨后在系統啟動階段會解析DTB文件，將相關資源注冊到Platform bus上。
http://lxr.linux.no/#linux+v2.6.25/arch/powerpc/sysdev/fsl_soc.c#L454
458static 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 < sizeof(int) || *addr > (1 << 10) - 1) {
?441??????????????????????? printk(KERN_WARNING "fsl_soc.c: invalid i2c device entry/n");
?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傳統的I2C驅動的設備列表。同時DTS文件中也需要描述，二者會利用of_find_i2c_driver進行匹配。
?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 < ARRAY_SIZE(i2c_devices); i++) {
?417??????????????? if (!of_device_is_compatible(node, i2c_devices[i].of_device))
?418??????????????????????? continue;
?419??????????????? if (strlcpy(info->driver_name, i2c_devices[i].i2c_driver,
?420??????????????????????????? KOBJ_NAME_LEN) >= KOBJ_NAME_LEN ||
?421??????????????????? strlcpy(info->type, i2c_devices[i].i2c_type,
?422??????????????????????????? I2C_NAME_SIZE) >= I2C_NAME_SIZE)
?423??????????????????????? return -ENOMEM;
?424??????????????? return 0;
?425??????? }
?426??????? return -ENODEV;
?427}
4.2??? platform driver
394
?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注冊時會掃描platform bus上的所有設備，匹配因子是fsl-i2c，匹配成功后調用fsl_i2c_probe將設備和驅動綁定起來，具體過程參加《詳解Linux2.6內核中基于platform機制的驅動模型》，隨后向系統注冊一個adapter。
http://blog.csdn.net/sailor_8318/archive/2010/01/29/5267698.aspx
318static 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 < 0) {
?333??????????????? result = -ENXIO;
?334??????????????? goto fail_get_irq;
?335??????? }
?336??????? i2c->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 controller/n");
?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)) < 0) {
?350??????????????????????? printk(KERN_ERR
?351?????????????????????????????? "i2c-mpc - failed to attach interrupt/n");
?352??????????????????????? goto fail_irq;
?353??????????????? }
?354
?355??????? mpc_i2c_setclock(i2c);
?356??????? platform_set_drvdata(pdev, i2c);
?357
?358??????? 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)) < 0) {
?363??????????????? printk(KERN_ERR "i2c-mpc - failed to add adapter/n");
?364??????????????? goto fail_add;
?365??????? }
?366
?367??????? return result;
?368
?369????? fail_add:
?370??????? if (i2c->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為platform data中的devid，為I2C的總線編號，其在設備樹文件中描述。
PowerPC的adapter驅動使用了i2c_add_numbered_adapter()注冊，總線號最初保存在 platform_data中。
4.3??? Adapter及algorithm
這一層主要是定義了關鍵的數據結構adapter和algorithm。
http://lxr.linux.no/#linux+v2.6.25/drivers/i2c/busses/i2c-mpc.c#L309
309static 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};
?308
http://lxr.linux.no/#linux+v2.6.25/drivers/i2c/busses/i2c-mpc.c#L256
256static 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 */? //一定程度上避免總線沖突，收發數據前先查詢總線狀態
?267??????? while (readb(i2c->base + MPC_I2C_SR) & CSR_MBB) {
?268??????????????? if (signal_pending(current)) {
?269??????????????????????? pr_debug("I2C: Interrupted/n");
?270??????????????????????? writeccr(i2c, 0);
?271??????????????????????? return -EINTR;
?272??????????????? }
?273??????????????? if (time_after(jiffies, orig_jiffies + HZ)) {
?274??????????????????????? pr_debug("I2C: timeout/n");
?275??????????????????????? if (readb(i2c->base + MPC_I2C_SR) ==
?276??????????????????????????? (CSR_MCF | CSR_MBB | CSR_RXAK))
?277??????????????????????????????? mpc_i2c_fixup(i2c);
?278??????????????????????? return -EIO;
?279??????????????? }
?280??????????????? schedule();
?281??????? }
?282
?283??????? for (i = 0; ret >= 0 && i < num; i++) {
?284??????????????? pmsg = &msgs[i];
?285??????????????? pr_debug("Doing %s %d bytes to 0x%02x - %d of %d messages/n",
?286???????????????????????? pmsg->flags & I2C_M_RD ? "read" : "write",
?287???????????????????????? pmsg->len, pmsg->addr, i + 1, num);
?288??????????????? if (pmsg->flags & I2C_M_RD)
?289??????????????????????? ret =
?290??????????????????????????? mpc_read(i2c, pmsg->addr, pmsg->buf, pmsg->len, i);
?291??????????????? else
?292??????????????????????? ret =
?293??????????????????????????? mpc_write(i2c, pmsg->addr, pmsg->buf, pmsg->len, i);
?294??????? }
?295??????? mpc_i2c_stop(i2c);
?296??????? return (ret < 0) ? ret : num;
?297}
5??? 硬件抽象層-I2C core
5.1??? 總線初始化?
http://lxr.linux.no/#linux+v2.6.25/drivers/i2c/i2c-core.c#L914
?885static int __init i2c_init(void)
?886{
?887??????? int retval;
?888
?889??????? retval = bus_register(&i2c_bus_type);
?890??????? if (retval)
?891??????????????? return retval;
?892??????? retval = class_register(&i2c_adapter_class);
?893??????? if (retval)
?894??????????????? goto bus_err;
?895??????? retval = i2c_add_driver(&dummy_driver);
?896??????? if (retval)
?897??????????????? goto class_err;
?898??????? return 0;
?899
?900class_err:
?901??????? class_unregister(&i2c_adapter_class);
?902bus_err:
?903??????? bus_unregister(&i2c_bus_type);
?904??????? return retval;
?905}
?906
?907static void __exit i2c_exit(void)
?908{
?909??????? i2c_del_driver(&dummy_driver);
?910??????? class_unregister(&i2c_adapter_class);
?911??????? bus_unregister(&i2c_bus_type);
?912}
?913
?914subsys_initcall(i2c_init);
?915module_exit(i2c_exit);
關于被subsys_initcall修飾的i2c_init何時初始化，請參考下文《詳解Linux2.6內核中基于platform機制的驅動模型》
http://blog.csdn.net/sailor_8318/archive/2010/01/29/5267698.aspx
此時platform bus及platform device已經注冊完畢，因此I2C控制器的相關資源已經就緒。
該過程主要完成了sysfs總線結構，最終形成如下結構：
/sys/bus/i2c/
|-- devices
|-- drivers
|?? |-- dummy
|????? |-- bind
|????? |-- uevent
|????? `-- unbind
|-- drivers_autoprobe
|-- drivers_probe
`-- uevent
和
/sys/class/i2c-adapter/
dummy_driver 僅僅是注冊了一個空的設備驅動，注冊驅動時會遍歷加載/sys/class/i2c-adapter/中的所有設備，該過程在初始化總線過程中完成， /sys/class/i2c-adapter/基本為空，所以我認為這里的驅動注冊只是驗證i2c總線結構的完整性考慮的。
5.2??? Adapter注冊
在 kernel中提供了兩個adapter注冊接口，分別為i2c_add_adapter()和i2c_add_numbered_adapter()。 由于在系統中可能存在多個adapter，因此每一條I2C總線對應一個編號，下文中稱為I2C總線號。對于i2c_add_adapter()而言， 它使用的是動態總線號，即由系統給其分配一個總線號，而i2c_add_numbered_adapter()則是自己指定總線號，如果這個總線號非法或者是被占用，就會注冊失敗。
http://lxr.linux.no/#linux+v2.6.25/drivers/i2c/i2c-core.c#L403
403static int i2c_register_adapter(struct i2c_adapter *adap)
?404{
?405??????? int res = 0, dummy;
?406
?407??????? mutex_init(&adap->bus_lock);
?408??????? mutex_init(&adap->clist_lock);
?409??????? INIT_LIST_HEAD(&adap->clients);
?410
?411??????? mutex_lock(&core_lock);
?412
?413??????? /* Add the adapter to the driver core.
?414???????? * If the parent pointer is not set up,
?415???????? * we add this adapter to the host bus.
?416???????? */
?417??????? if (adap->dev.parent == NULL) {
?418??????????????? adap->dev.parent = &platform_bus;
?419??????????????? pr_debug("I2C adapter driver [%s] forgot to specify "
?420???????????????????????? "physical device/n", adap->name);
?421??????? }
?422??????? sprintf(adap->dev.bus_id, "i2c-%d", adap->nr);
?423??????? adap->dev.release = &i2c_adapter_dev_release;
?424??????? adap->dev.class = &i2c_adapter_class;
?425??????? res = device_register(&adap->dev);
?426??????? if (res)
?427??????????????? goto out_list;
?428
?429??????? dev_dbg(&adap->dev, "adapter [%s] registered/n", adap->name);
?430
?431??????? /* create pre-declared device nodes for new-style drivers */
?432??????? if (adap->nr < __i2c_first_dynamic_bus_num)
?433??????????????? i2c_scan_static_board_info(adap); //完成靜態定義的I2C設備的掃描，將設備和adapter掛上鉤，即將設備掛在總線上
?434
?435??????? /* let legacy drivers scan this bus for matching devices */
?436??????? dummy = bus_for_each_drv(&i2c_bus_type, NULL, adap,
?437???????????????????????????????? i2c_do_add_adapter); /*探測總線上的所有i2c設備驅動，如果匹配則完成client、driver、device、adapter的綁定*/??
?438
?439out_unlock:
?440??????? mutex_unlock(&core_lock);
?441??????? return res;
?442
?443out_list:
?444??????? idr_remove(&i2c_adapter_idr, adap->nr);
?445??????? goto out_unlock;
?446}
5.3??? 驅動注冊
http://lxr.linux.no/#linux+v2.6.25/drivers/i2c/i2c-core.c#L635
635int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
?636{
?637??????? int res;
?638
?639??????? /* new style driver methods can't mix with legacy ones */
?640??????? if (is_newstyle_driver(driver)) {
?641??????????????? if (driver->attach_adapter || driver->detach_adapter
?642??????????????????????????????? || driver->detach_client) {
?643??????????????????????? printk(KERN_WARNING
?644??????????????????????????????????????? "i2c-core: driver [%s] is confused/n",
?645??????????????????????????????????????? driver->driver.name);
?646??????????????????????? return -EINVAL;
?647??????????????? }
?648??????? }
?649
?650??????? /* add the driver to the list of i2c drivers in the driver core */
?651??????? driver->driver.owner = owner;
?652??????? driver->driver.bus = &i2c_bus_type;
?653
?654??????? /* for new style drivers, when registration returns the driver core
?655???????? * will have called probe() for all matching-but-unbound devices.
?656???????? */
?657??????? res = driver_register(&driver->driver);
?658??????? if (res)
?659??????????????? return res;
?660
?661??????? mutex_lock(&core_lock);
?662
?663??????? pr_debug("i2c-core: driver [%s] registered/n", driver->driver.name);
?664
?665??????? /* legacy drivers scan i2c busses directly */
?666??????? if (driver->attach_adapter) {
?667??????????????? struct i2c_adapter *adapter;
?668
?669??????????????? down(&i2c_adapter_class.sem);
?670??????????????? list_for_each_entry(adapter, &i2c_adapter_class.devices,
?671??????????????????????????????????? dev.node) {
?672??????????????????????? driver->attach_adapter(adapter);
?673??????????????? }
?674??????????????? up(&i2c_adapter_class.sem);
?675??????? }
?676
?677??????? mutex_unlock(&core_lock);
?678??????? return 0;
?679}
?680EXPORT_SYMBOL(i2c_register_driver);
兩種注冊方式。對于new style驅動，將采用內核通用的驅動模型，其流程和platform driver的注冊過程類似，請請參考下文《詳解Linux2.6內核中基于platform機制的驅動模型》
http://blog.csdn.net/sailor_8318/archive/2010/01/29/5267698.aspx
而對于legacy driver，是如何匹配注冊的呢？TBD
5.4??? 數據傳輸
917/* ----------------------------------------------------
?918 * the functional interface to the i2c busses.
?919 * ----------------------------------------------------
?920 */
?921
?922int i2c_transfer(struct i2c_adapter * adap, struct i2c_msg *msgs, int num)
?923{
?924??????? int ret;
?925
?926??????? if (adap->algo->master_xfer) {
?927#ifdef DEBUG
?928??????????????? for (ret = 0; ret < num; ret++) {
?929??????????????????????? dev_dbg(&adap->dev, "master_xfer[%d] %c, addr=0x%02x, "
?930??????????????????????????????? "len=%d%s/n", ret, (msgs[ret].flags & I2C_M_RD)
?931??????????????????????????????? ? 'R' : 'W', msgs[ret].addr, msgs[ret].len,
?932??????????????????????????????? (msgs[ret].flags & I2C_M_RECV_LEN) ? "+" : "");
?933??????????????? }
?934#endif
?935
?936??????????????? if (in_atomic() || irqs_disabled()) { //原子上下文或者中斷禁止時不能獲取自旋鎖，防止休眠死鎖，只能試探鎖
?937??????????????????????? ret = mutex_trylock(&adap->bus_lock);
?938??????????????????????? if (!ret)
?939??????????????????????????????? /* I2C activity is ongoing. */
?940??????????????????????????????? return -EAGAIN;
?941??????????????? } else {
?942??????????????????????? mutex_lock_nested(&adap->bus_lock, adap->level);
?943??????????????? }
?944
?945??????????????? ret = adap->algo->master_xfer(adap,msgs,num);
?946??????????????? mutex_unlock(&adap->bus_lock);
?947
?948??????????????? return ret;
?949??????? } else {
?950??????????????? dev_dbg(&adap->dev, "I2C level transfers not supported/n");
?951??????????????? return -ENOSYS;
?952??????? }
?953}
?954EXPORT_SYMBOL(i2c_transfer);
核心層提供的通用數據收發接口，屏蔽了底層差異。利用adapter進行數據傳輸前先獲得互斥鎖，因此保證只有一個調用者占用總線，這樣數據傳輸才是原子的。多個msgs可以一次傳輸完畢，因此對于讀操作，兩次I2C總線的訪問（先寫后讀）需要在一個io ctrl中處理完畢
6??? 用戶接口層-I2C設備驅動
6.1??? 統一的設備模型
此驅動模型是針對I2C控制器的，因為對I2C slave的尋址是通過報文的內容來實現的，而對于I2C控制器來說，slave的地址僅僅是某個具體的報文而已，對控制器來說是透明的，因此用戶空間訪問的設備本質上就是I2C控制器。
6.1.1??? 關鍵數據結構
550static struct i2c_driver i2cdev_driver = {
?551??????? .driver = {
?552??????????????? .name?? = "dev_driver",
?553??????? },
?554??????? .id???????????? = I2C_DRIVERID_I2CDEV,
?555??????? .attach_adapter = i2cdev_attach_adapter,
?556??????? .detach_adapter = i2cdev_detach_adapter,
?557??????? .detach_client? = i2cdev_detach_client,
?558};
定義了一個標準的i2c_driver。
? 41/*
? 42 * An i2c_dev represents an i2c_adapter ... an I2C or SMBus master, not a
? 43 * slave (i2c_client) with which messages will be exchanged.? It's coupled
? 44 * with a character special file which is accessed by user mode drivers.
? 45 *
? 46 * The list of i2c_dev structures is parallel to the i2c_adapter lists
? 47 * maintained by the driver model, and is updated using notifications
? 48 * delivered to the i2cdev_driver.
? 49 */
? 50struct i2c_dev {
? 51??????? struct list_head list;
? 52??????? struct i2c_adapter *adap;
? 53??????? struct device *dev;
? 54};
? 55
? 56#define I2C_MINORS????? 256
? 57static LIST_HEAD(i2c_dev_list);
? 58static DEFINE_SPINLOCK(i2c_dev_list_lock);
定義了一個i2c_dev列表，每個adapter對應一個i2c_dev。
478static const struct file_operations i2cdev_fops = {
?479??????? .owner????????? = THIS_MODULE,
?480??????? .llseek???????? = no_llseek,
?481??????? .read?????????? = i2cdev_read,
?482??????? .write????????? = i2cdev_write,
?483??????? .ioctl????????? = i2cdev_ioctl,
?484??????? .open?????????? = i2cdev_open,
?485??????? .release??????? = i2cdev_release,
?486};
?487
任意一個需要和用戶空間通信的驅動必備的數據結構，其定義了具體的讀寫操作方法。
6.1.2??? 初始化
http://lxr.linux.no/#linux+v2.6.25/drivers/i2c/i2c-dev.c#L607
566static int __init i2c_dev_init(void)
?567{
?568??????? int res;
?569
?570??????? printk(KERN_INFO "i2c /dev entries driver/n");
?571
?572??????? res = register_chrdev(I2C_MAJOR, "i2c", &i2cdev_fops);
?573??????? if (res)
?574??????????????? goto out;
?575
?576??????? i2c_dev_class = class_create(THIS_MODULE, "i2c-dev");
?577??????? if (IS_ERR(i2c_dev_class))
?578??????????????? goto out_unreg_chrdev;
?579
?580??????? res = i2c_add_driver(&i2cdev_driver);
?581??????? if (res)
?582??????????????? goto out_unreg_class;
?583
?584??????? return 0;
?585
?586out_unreg_class:
?587??????? class_destroy(i2c_dev_class);
?588out_unreg_chrdev:
?589??????? unregister_chrdev(I2C_MAJOR, "i2c");
?590out:
?591??????? printk(KERN_ERR "%s: Driver Initialisation failed/n", __FILE__);
?592??????? return res;
?593}
?594
?595static void __exit i2c_dev_exit(void)
?596{
?597??????? i2c_del_driver(&i2cdev_driver);
?598??????? class_destroy(i2c_dev_class);
?599??????? unregister_chrdev(I2C_MAJOR,"i2c");
?600}
首先注冊了一個字符型設備驅動，然后注冊i2c_driver，將驅動和adapter綁定起來，匹配成功后將調用i2c_driver 的attach_adapter 方法，即i2cdev_attach_adapter， 建立dev設備節點，并維護了一個i2c_dev鏈表保存設備節點和adapter的關系。
http://lxr.linux.no/#linux+v2.6.25/drivers/i2c/i2c-dev.c#L498
498static int i2cdev_attach_adapter(struct i2c_adapter *adap)
?499{
?500??????? struct i2c_dev *i2c_dev;
?501??????? int res;
?502
?503??????? i2c_dev = get_free_i2c_dev(adap);? //添加一個adapter到i2c_dev列表中
?504??????? if (IS_ERR(i2c_dev))
?505??????????????? return PTR_ERR(i2c_dev);
?506
?507??????? /* register this i2c device with the driver core */
?508??????? i2c_dev->dev = device_create(i2c_dev_class, &adap->dev,
?509???????????????????????????????????? MKDEV(I2C_MAJOR, adap->nr),
?510???????????????????????????????????? "i2c-%d", adap->nr);
?511??????? if (IS_ERR(i2c_dev->dev)) {
?512??????????????? res = PTR_ERR(i2c_dev->dev);
?513??????????????? goto error;
?514??????? }
?515??????? res = device_create_file(i2c_dev->dev, &dev_attr_name);
?516??????? if (res)
?517??????????????? goto error_destroy;
?518
?519??????? pr_debug("i2c-dev: adapter [%s] registered as minor %d/n",
?520???????????????? adap->name, adap->nr);
?521??????? return 0;
?522error_destroy:
?523??????? device_destroy(i2c_dev_class, MKDEV(I2C_MAJOR, adap->nr));
?524error:
?525??????? return_i2c_dev(i2c_dev);
?526??????? return res;
?527}
以I2C_MAJOR和adap->nr為主從設備號注冊設備節點，如果系統有udev或者是hotplug，那么就么在/dev下自動創建相關的設備節點了
6.1.3??? Open及release
431static int i2cdev_open(struct inode *inode, struct file *file)
?432{
?433??????? unsigned int minor = iminor(inode);
?434??????? struct i2c_client *client;
?435??????? struct i2c_adapter *adap;
?436??????? struct i2c_dev *i2c_dev;
?437
?438??????? i2c_dev = i2c_dev_get_by_minor(minor); //由次設備號獲得i2c_dev即可獲得對應的adapter
?439??????? if (!i2c_dev)
?440??????????????? return -ENODEV;
?441
?442??????? adap = i2c_get_adapter(i2c_dev->adap->nr);? //對module引用進行計數
?443??????? if (!adap)
?444??????????????? return -ENODEV;
?445
?446??????? /* This creates an anonymous i2c_client, which may later be
?447???????? * pointed to some address using I2C_SLAVE or I2C_SLAVE_FORCE.
?448???????? *
?449???????? * This client is ** NEVER REGISTERED ** with the driver model
?450???????? * or I2C core code!!? It just holds private copies of addressing
?451???????? * information and maybe a PEC flag.
?452???????? */
?453??????? client = kzalloc(sizeof(*client), GFP_KERNEL);
?454??????? if (!client) {
?455??????????????? i2c_put_adapter(adap);
?456??????????????? return -ENOMEM;
?457??????? }
?458??????? snprintf(client->name, I2C_NAME_SIZE, "i2c-dev %d", adap->nr);
?459??????? client->driver = &i2cdev_driver;
?460
?461??????? client->adapter = adap;
?462??????? file->private_data = client;
?463
?464??????? return 0;
?465}
Open操作是用戶空間程序和內核驅動交換的第一步，最終返回給用戶空間的就是struct file結構體。對于I2C 驅動來說，用戶空間所獲得的就是client這個關鍵信息，在其中可以找到所有有關的信息如client所在的adapter及i2c_driver。此i2c_client并沒有遵循設備模型的方式注冊進系統，在sys下面沒有任何信息。
6.1.4??? 數據收發
對于I2C驅動來說，數據收發有兩種途徑，read/write或者ioctl方式。
對于read/write方式來說，必須先通過ioctl的I2C_SLAVE設置從設備的地址。隨后再通過read/write對相應的slave直接進行數據收發。
117/*
?118 * After opening an instance of this character special file, a file
?119 * descriptor starts out associated only with an i2c_adapter (and bus).
?120 *
?121 * Using the I2C_RDWR ioctl(), you can then *immediately* issue i2c_msg
?122 * traffic to any devices on the bus used by that adapter.? That's because
?123 * the i2c_msg vectors embed all the addressing information they need, and
?124 * are submitted directly to an i2c_adapter.? However, SMBus-only adapters
?125 * don't support that interface.
?126 *
?127 * To use read()/write() system calls on that file descriptor, or to use
?128 * SMBus interfaces (and work with SMBus-only hosts!), you must first issue
?129 * an I2C_SLAVE (or I2C_SLAVE_FORCE) ioctl.? That configures an anonymous
?130 * (never registered) i2c_client so it holds the addressing information
?131 * needed by those system calls and by this SMBus interface.
?132 */
?133
?134static ssize_t i2cdev_read (struct file *file, char __user *buf, size_t count,
?135??????????????????????????? loff_t *offset)
?136{
read/write與用戶空間的接口是buf和count，為收發的相應數據指針和數據長度。
SMBus只能利用read/write方式和用戶空間通信？？
對于ioctl方式，相關的cmd是I2C_RDWR
203static int i2cdev_ioctl(struct inode *inode, struct file *file,
?204??????????????? unsigned int cmd, unsigned long arg)
?205{
?206??????? struct i2c_client *client = (struct i2c_client *)file->private_data;
?207??????? struct i2c_rdwr_ioctl_data rdwr_arg;
?208??????? struct i2c_smbus_ioctl_data data_arg;
?209??????? union i2c_smbus_data temp;
?210??????? struct i2c_msg *rdwr_pa;
?211??????? u8 __user **data_ptrs;
?212??????? int i,datasize,res;
?213??????? unsigned long funcs;
255??????? case I2C_RDWR:
?256??????????????? if (copy_from_user(&rdwr_arg,
?257?????????????????????????????????? (struct i2c_rdwr_ioctl_data __user *)arg,
?258?????????????????????????????????? sizeof(rdwr_arg)))
?259??????????????????????? return -EFAULT;
?260
?261??????????????? /* Put an arbitrary limit on the number of messages that can
?262???????????????? * be sent at once */
?263??????????????? if (rdwr_arg.nmsgs > I2C_RDRW_IOCTL_MAX_MSGS)
?264??????????????????????? return -EINVAL;
?265
?266??????????????? rdwr_pa = (struct i2c_msg *)
?267??????????????????????? kmalloc(rdwr_arg.nmsgs * sizeof(struct i2c_msg),
?268??????????????????????? GFP_KERNEL);
?269
?270??????????????? if (rdwr_pa == NULL) return -ENOMEM;
?271
?272??????????????? if (copy_from_user(rdwr_pa, rdwr_arg.msgs,
?273?????????????????????????????????? rdwr_arg.nmsgs * sizeof(struct i2c_msg))) {
?274??????????????????????? kfree(rdwr_pa);
?275??????????????????????? return -EFAULT;
?276??????????????? }
?277
?278??????????????? data_ptrs = kmalloc(rdwr_arg.nmsgs * sizeof(u8 __user *), GFP_KERNEL);
?279??????????????? if (data_ptrs == NULL) {
?280??????????????????????? kfree(rdwr_pa);
?281??????????????????????? return -ENOMEM;
?282??????????????? }
?283
?284??????????????? res = 0;
?285??????????????? for( i=0; i<rdwr_arg.nmsgs; i++ ) {
?286??????????????????????? /* Limit the size of the message to a sane amount;
?287???????????????????????? * and don't let length change either. */
?288??????????????????????? if ((rdwr_pa[i].len > 8192) ||
?289??????????????????????????? (rdwr_pa[i].flags & I2C_M_RECV_LEN)) {
?290??????????????????????????????? res = -EINVAL;
?291??????????????????????????????? break;
?292??????????????????????? }
?293??????????????????????? data_ptrs[i] = (u8 __user *)rdwr_pa[i].buf;
?294??????????????????????? rdwr_pa[i].buf = kmalloc(rdwr_pa[i].len, GFP_KERNEL);
?295??????????????????????? if(rdwr_pa[i].buf == NULL) {
?296??????????????????????????????? res = -ENOMEM;
?297??????????????????????????????? break;
?298??????????????????????? }
?299??????????????????????? if(copy_from_user(rdwr_pa[i].buf,
?300??????????????????????????????? data_ptrs[i],
?301??????????????????????????????? rdwr_pa[i].len)) {
?302??????????????????????????????????????? ++i; /* Needs to be kfreed too */
?303??????????????????????????????????????? res = -EFAULT;
?304??????????????????????????????? break;
?305??????????????????????? }
?306??????????????? }
?307??????????????? if (res < 0) {
?308??????????????????????? int j;
?309??????????????????????? for (j = 0; j < i; ++j)
?310??????????????????????????????? kfree(rdwr_pa[j].buf);
?311??????????????????????? kfree(data_ptrs);
?312??????????????????????? kfree(rdwr_pa);
?313??????????????????????? return res;
?314??????????????? }
?315
//上述所有操作就是將用戶空間的數據拷貝到內核空間。組織成以rdwr_pa為首地址的nmsgs個msg
?316??????????????? res = i2c_transfer(client->adapter,
?317??????????????????????? rdwr_pa,
?318??????????????????????? rdwr_arg.nmsgs);
?319??????????????? while(i-- > 0) {
?320??????????????????????? if( res>=0 && (rdwr_pa[i].flags & I2C_M_RD)) {
?321??????????????????????????????? if(copy_to_user(? //如果是讀操作，再將內核空間中緩存的數據拷貝到用戶空間
?322??????????????????????????????????????? data_ptrs[i],
?323??????????????????????????????????????? rdwr_pa[i].buf,
?324??????????????????????????????????????? rdwr_pa[i].len)) {
?325??????????????????????????????????????? res = -EFAULT;
?326??????????????????????????????? }
?327??????????????????????? }
?328??????????????????????? kfree(rdwr_pa[i].buf);
?329??????????????? }
?330??????????????? kfree(data_ptrs);
?331??????????????? kfree(rdwr_pa);
?332??????????????? return res;
與用戶空間的接口是i2c_rdwr_ioctl_data
/* This is the structure as used in the I2C_RDWR ioctl call */
struct i2c_rdwr_ioctl_data {
??? struct i2c_msg __user *msgs;??? /* pointers to i2c_msgs */
??? __u32 nmsgs;??? ??? ??? /* number of i2c_msgs */
};
所有待收發的數據都已經由用戶空間組織好了
/**
?* struct i2c_msg - an I2C transaction segment beginning with START
?* @addr: Slave address, either seven or ten bits.? When this is a ten
?*??? bit address, I2C_M_TEN must be set in @flags and the adapter
?*??? must support I2C_FUNC_10BIT_ADDR.
?* @flags: I2C_M_RD is handled by all adapters.? No other flags may be
?*??? provided unless the adapter exported the relevant I2C_FUNC_*
?*??? flags through i2c_check_functionality().
?* @len: Number of data bytes in @buf being read from or written to the
?*??? I2C slave address.? For read transactions where I2C_M_RECV_LEN
?*??? is set, the caller guarantees that this buffer can hold up to
?*??? 32 bytes in addition to the initial length byte sent by the
?*??? slave (plus, if used, the SMBus PEC); and this value will be
?*??? incremented by the number of block data bytes received.
?* @buf: The buffer into which data is read, or from which it's written.
?*
?* An i2c_msg is the low level representation of one segment of an I2C
?* transaction.? It is visible to drivers in the @i2c_transfer() procedure,
?* to userspace from i2c-dev, and to I2C adapter drivers through the
?* @i2c_adapter.@master_xfer() method.
?*
?* Except when I2C "protocol mangling" is used, all I2C adapters implement
?* the standard rules for I2C transactions.? Each transaction begins with a
?* START.? That is followed by the slave address, and a bit encoding read
?* versus write.? Then follow all the data bytes, possibly including a byte
?* with SMBus PEC.? The transfer terminates with a NAK, or when all those
?* bytes have been transferred and ACKed.? If this is the last message in a
?* group, it is followed by a STOP.? Otherwise it is followed by the next
?* @i2c_msg transaction segment, beginning with a (repeated) START.
?*
?* Alternatively, when the adapter supports I2C_FUNC_PROTOCOL_MANGLING then
?* passing certain @flags may have changed those standard protocol behaviors.
?* Those flags are only for use with broken/nonconforming slaves, and with
?* adapters which are known to support the specific mangling options they
?* need (one or more of IGNORE_NAK, NO_RD_ACK, NOSTART, and REV_DIR_ADDR).
?*/
struct i2c_msg {
??? __u16 addr;??? /* slave address??? ??? ??? */
??? __u16 flags;
#define I2C_M_TEN??? ??? 0x0010??? /* this is a ten bit chip address */
#define I2C_M_RD??? ??? 0x0001??? /* read data, from slave to master */
。。。
#define I2C_M_RECV_LEN??? ??? 0x0400??? /* length will be first received byte */
??? __u16 len;??? ??? /* msg length??? ??? ??? ??? */
??? __u8 *buf;??? ??? /* pointer to msg data??? ??? ??? */
};
6.2??? 特定的設備驅動
原則上所有的I2C從設備的方法都可以通過上述統一的設備模型I2c-dev來訪問，但I2c-dev上傳輸的是透明的數據，而對于某些I2C從設備，其數據傳輸遵循一定的格式，如果用I2c-dev來訪問，則用戶需要組織好所有的i2c_msg，對一般用戶來說可能比較復雜。為了提供更加user friendly的接口，可以對特定I2C從設備的訪問進行再次封裝。
如I2C的RTC，其數據的轉換較為復雜，為了減少用戶空間的轉換，提供了專用的RTC驅動供用戶程序訪問，其向上屏蔽了具體RTC芯片的差異。
下面以drivers/rtc/rtc-pcf8563.c為例來進行講述。
6.2.1??? 關鍵數據結構
struct pcf8563 {
??? struct i2c_client client;
??? /*
??? ?* The meaning of MO_C bit varies by the chip type.
??? ?* From PCF8563 datasheet: this bit is toggled when the years
??? ?* register overflows from 99 to 00
??? ?*?? 0 indicates the century is 20xx
??? ?*?? 1 indicates the century is 19xx
??? ?* From RTC8564 datasheet: this bit indicates change of
??? ?* century. When the year digit data overflows from 99 to 00,
??? ?* this bit is set. By presetting it to 0 while still in the
??? ?* 20th century, it will be set in year 2000, ...
??? ?* There seems no reliable way to know how the system use this
??? ?* bit.? So let's do it heuristically, assuming we are live in
??? ?* 1970...2069.
??? ?*/
??? int c_polarity;??? /* 0: MO_C=1 means 19xx, otherwise MO_C=1 means 20xx */
};
pcf8563關鍵信息的全局表示。
static struct i2c_driver pcf8563_driver = {
??? .driver??? ??? = {
??? ??? .name??? = "pcf8563",
??? },
??? .id??? ??? = I2C_DRIVERID_PCF8563,
??? .attach_adapter = &pcf8563_attach,
??? .detach_client??? = &pcf8563_detach,
};
特定的pcf8563_driver，有自己特定的pcf8563_attach方法。
static const struct rtc_class_ops pcf8563_rtc_ops = {
??? .read_time??? = pcf8563_rtc_read_time,
??? .set_time??? = pcf8563_rtc_set_time,
};
向RTC子系統注冊的讀寫方法。
6.2.2??? 初始化
static int __init pcf8563_init(void)
{
??? return i2c_add_driver(&pcf8563_driver);
}
static void __exit pcf8563_exit(void)
{
??? i2c_del_driver(&pcf8563_driver);
}
調用i2c_add_driver向I2C總線上注冊pcf8563_driver的I2C驅動，根據pcf8563這個driver的name進行匹配，匹配成功后將自動調用pcf8563_attach。
static int pcf8563_probe(struct i2c_adapter *adapter, int address, int kind)
{
??? struct pcf8563 *pcf8563;
??? struct i2c_client *client;
??? struct rtc_device *rtc;
??? int err = 0;
??? dev_dbg(&adapter->dev, "%s/n", __FUNCTION__);
??? if (!i2c_check_functionality(adapter, I2C_FUNC_I2C)) {
??? ??? err = -ENODEV;
??? ??? goto exit;
??? }
??? if (!(pcf8563 = kzalloc(sizeof(struct pcf8563), GFP_KERNEL))) {
??? ??? err = -ENOMEM;
??? ??? goto exit;
??? }
??? client = &pcf8563->client;
??? client->addr = address;? //此address即為該slave的I2C設備地址
??? client->driver = &pcf8563_driver;
??? client->adapter??? = adapter;
//上述幾步和統一的I2C設備模型的client一樣
??? strlcpy(client->name, pcf8563_driver.driver.name, I2C_NAME_SIZE);
??? /* Verify the chip is really an PCF8563 */
??? if (kind < 0) {
??? ??? if (pcf8563_validate_client(client) < 0) {? //探測相關slave是否存在，簡單的收發數據進行驗證
??? ??? ??? err = -ENODEV;
??? ??? ??? goto exit_kfree;
??? ??? }
??? }
??? /* Inform the i2c layer */
??? if ((err = i2c_attach_client(client)))? //將本client掛接到依附的adapter上??? ??? goto exit_kfree;
??? dev_info(&client->dev, "chip found, driver version " DRV_VERSION "/n");
??? rtc = rtc_device_register(pcf8563_driver.driver.name, &client->dev,
??? ??? ??? ??? &pcf8563_rtc_ops, THIS_MODULE);
//向RTC子系統注冊pcf8563設備
??? if (IS_ERR(rtc)) {
??? ??? err = PTR_ERR(rtc);
??? ??? goto exit_detach;
??? }
??? i2c_set_clientdata(client, rtc);
??? return 0;
exit_detach:
??? i2c_detach_client(client);
exit_kfree:
??? kfree(pcf8563);
exit:
??? return err;
}
6.2.3??? 數據收發
RTC設備的數據收發是通過drivers/rtc/rtc-dev.c進行的。
static const struct file_operations rtc_dev_fops = {
??? .owner??? ??? = THIS_MODULE,
??? .llseek??? ??? = no_llseek,
??? .read??? ??? = rtc_dev_read,
??? .poll??? ??? = rtc_dev_poll,
??? .ioctl??? ??? = rtc_dev_ioctl,
??? .open??? ??? = rtc_dev_open,
??? .release??? = rtc_dev_release,
??? .fasync??? ??? = rtc_dev_fasync,
};
該file_operations向用戶空間提供了統一接口。
7??? 驅動訪問示例
下面以一款EEPOM AT24C64AN為例來講述用戶空間如何訪問I2C設備。
7.1.1??? 寫操作
I2C總線的寫操作通常比較簡單，分為byte write和page write
?
但兩種方式對于SW來說沒有區別，SW只需要指定發送的數據長度即可。
/**********
i2cBus為總線編號，也就是adapter編號，應該是本I2C設備所掛接的I2C總線
devAddr，為待訪問的I2C設備地址
bTwoByteAddr，為待訪問的從設備內部寄存器偏移量地址的寬度，即8位或16位，對應1或2個字節
offAddr，為待訪問的從設備內部寄存器偏移量起始地址
byteLen，待寫的數據長度，不包括總線協議上的dev addr及word address
i2cBuff1，待發送到有效數據即DATA
********/
int i2c_write(BYTE i2cBus, BYTE devAddr, BOOL bTwoByteAddr,
?????????????????????????? WORD offAddr, WORD byteLen, BYTE* i2cBuff1)
{
? char?? fileName[20];
? BYTE?? i2cBuff0[256];?? /* buffer to send offset address & data*/
? int??? file, iRealDataStart;
??
? sprintf(fileName, "/dev/i2c-%d", i2cBus);? //打開相應的I2C總線設備
??
? file = open(fileName, O_RDWR);
? if (file < 0)
? {
??? fprintf(stderr, "Fail: Could not open file `/dev/i2c-%d': %s/n", /
??? i2cBus, strerror(ENOENT));
??? return -1;
? }
??
? if(!bTwoByteAddr)
? {
??? i2cBuff0[0] = (BYTE)(offAddr & 0x00FF);
??? iRealDataStart = 1;
? }
? else
? {
??? i2cBuff0[0] = (BYTE)((offAddr & 0xFF00)>>8);
??? i2cBuff0[1] = (BYTE)(offAddr & 0x00FF);
??? iRealDataStart = 2;
? }
??
? /* Build write buffer */
? memcpy(&i2cBuff0[iRealDataStart], i2cBuff1, byteLen);? //構造i2c_msg中的buf
??
? sI2ccMessages[0].addr = devAddr;
? sI2ccMessages[0].flags = 0; /* Write flag = 0 */
? sI2ccMessages[0].len = byteLen + iRealDataStart;? //此長度為DATA和WORD ADDRESS
? sI2ccMessages[0].buf = i2cBuff0;
??
? sI2ccIoctData.msgs = sI2ccMessages;
? sI2ccIoctData.nmsgs = 1;
??
? if (ioctl(file, I2C_RDWR, &sI2ccIoctData) < 0)
? {
??? fprintf(stderr, "Fail: fails to write to I2C device 0x%x at address 0x%x/n", devAddr, offAddr);
??? close(file);
??? return -1;
? }
??
? close(file);
??
? return 0;
}
7.1.2??? 讀操作
I2C設備的讀操作較復雜，需要先寫待讀的內部寄存器地址，然后再發起總線的讀操作。時序如下：
?
因此需要在總線上連續進行兩次數據傳輸，即兩個i2c_msg。
/**********
i2cBus為總線編號，也就是adapter編號，應該是本I2C設備所掛接的I2C總線
devAddr，為待訪問的I2C設備地址
bTwoByteAddr，為待訪問的從設備內部寄存器偏移量地址的寬度，即8位或16位，對應1或2個字節
offAddr，為待訪問的從設備內部寄存器偏移量起始地址
byteLen，待讀的數據長度
i2cBuff1，待讀的有效數據即DATA
********/
int i2c_read(BYTE i2cBus, BYTE devAddr, BOOL bTwoByteAddr,
?????????????????????????? WORD offAddr, WORD byteLen, BYTE* i2cBuff1)
{
? char?? fileName[20];
? BYTE?? i2cBuff0[2];???? /* buffer to send offset address */
? int??? file= 0;
??
? sprintf(fileName, "/dev/i2c-%d", i2cBus);
??
? file = open(fileName, O_RDWR);
? if (file < 0)
? {
??? fprintf(stderr, "Fail: Could not open file `/dev/i2c-%d': %s/n", /
??????????? i2cBus, strerror(ENOENT));
????
??? return -1;
? }
??
? sI2ccMessages[0].addr = devAddr;
? sI2ccMessages[0].flags = 0; /* write flag = 0 */
??
? if(!bTwoByteAddr)
? {
??? i2cBuff0[0] = (BYTE)(offAddr & 0x00FF);
??? sI2ccMessages[0].len = 1;??
? }
? else
? {
??? i2cBuff0[0] = (BYTE)((offAddr& 0xFF00)>>8);
??? i2cBuff0[1] = (BYTE)(offAddr& 0x00FF);
??? sI2ccMessages[0].len = 2;
? }
? sI2ccMessages[0].buf = i2cBuff0;? //第一個msg只是一個默認的寫操作
??
? sI2ccMessages[1].addr = devAddr;
? sI2ccMessages[1].flags = I2C_M_RD; /* read flag */
? sI2ccMessages[1].len = byteLen;
? sI2ccMessages[1].buf = i2cBuff1;? //此僅僅為DATA域
??
? sI2ccIoctData.msgs = sI2ccMessages;
? sI2ccIoctData.nmsgs = 2;
??
? if (ioctl(file, I2C_RDWR, &sI2ccIoctData) < 0)? //一個ioctl必須連續發送兩個msg
? {
??? fprintf(stderr, "Fail: fails to read from I2C device 0x%x at address 0x%x/n", /
??????????? devAddr, offAddr);
??? close(file);
??? return -1;
? }
??
? close(file);
? return 0;
}
8??? 參考鳴謝
http：//blog.chinaunix.net/u1/51562/showart_1403925.html
http：//blog.csdn.net/tjd0227/archive/2010/07/21/5753606.aspx
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