i2cdrivers

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转载于：http://blog.csdn.net/liuhaoyutz

内核版本：3.10.1

编写一个I2C设备驱动程序的工作可分为两部分，一是定义和注册I2C设备，即i2c_client；二是定义和注册I2C设备驱动，即i2c_driver。下面我们就以mini2440的I2C设备at24c08 EEPROM为例，介绍如何完成这两个工作。

一、定义和注册I2C设备

步骤1：用i2c_board_info保存I2C设备相关信息

在Linux中，struct i2c_client代表一个I2C设备，该结构体定义在include/linux/i2c.h文件中：

[cpp] view plain copy

200/**
201 * struct i2c_client - represent an I2Cslave device
202 * @flags: I2C_CLIENT_TEN indicates thedevice uses a ten bit chip address;
203 * I2C_CLIENT_PEC indicates it uses SMBus Packet Error Checking
204 * @addr: Address used on the I2C busconnected to the parent adapter.
205 * @name: Indicates the type of thedevice, usually a chip name that's
206 * generic enough to hide second-sourcing and compatible revisions.
207 * @adapter: manages the bus segmenthosting this I2C device
208 * @driver: device's driver, hencepointer to access routines
209 * @dev: Driver model device node forthe slave.
210 * @irq: indicates the IRQ generated bythis device (if any)
211 * @detected: member of ani2c_driver.clients list or i2c-core's
212 * userspace_devices list
213 *
214 * An i2c_client identifies a singledevice (i.e. chip) connected to an
215 * i2c bus. The behaviour exposed to Linuxis defined by the driver
216 * managing the device.
217 */
218struct i2c_client {
219 unsigned short flags; /*div., see below */
220 unsigned short addr; /*chip address - NOTE: 7bit */
221 /* addresses are stored inthe */
222 /* _LOWER_ 7 bits */
223 char name[I2C_NAME_SIZE];
224 struct i2c_adapter *adapter; /*the adapter we sit on */
225 struct i2c_driver *driver; /* andour access routines */
226 struct device dev; /* thedevice structure */
227 int irq; /* irq issuedby device */
228 struct list_head detected;
229};

我们不用直接定义一个i2c_client结构，Linux会根据I2C设备的相关信息自动创建i2c_client。所以，我们需要提供I2C设备的相关信息。对于Mini2440的I2C设备at24c08 EEPROM，其相关信息保存在arch/arm/mach-s3c24xx/mach-mini2440.c文件中：

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485/*
486 * I2C devices
487 */
488static struct at24_platform_data at24c08= {
489 .byte_len = SZ_8K / 8,
490 .page_size = 16,
491};
492
493static struct i2c_board_infomini2440_i2c_devs[] __initdata = {
494 {
495 I2C_BOARD_INFO("24c08", 0x50),
496 .platform_data = &at24c08,
497 },
498};

struct i2c_board_info是创建i2c设备的模板，该结构体定义在include/linux/i2c.h文件中：

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251/**
252 * struct i2c_board_info - template fordevice creation
253 * @type: chip type, to initializei2c_client.name
254 * @flags: to initializei2c_client.flags
255 * @addr: stored in i2c_client.addr
256 * @platform_data: stored ini2c_client.dev.platform_data
257 * @archdata: copied intoi2c_client.dev.archdata
258 * @of_node: pointer to OpenFirmwaredevice node
259 * @acpi_node: ACPI device node
260 * @irq: stored in i2c_client.irq
261 *
262 * I2C doesn't actually support hardwareprobing, although controllers and
263 * devices may be able to useI2C_SMBUS_QUICK to tell whether or not there's
264 * a device at a given address. Drivers commonly need more information than
265 * that, such as chip type,configuration, associated IRQ, and so on.
266 *
267 * i2c_board_info is used to buildtables of information listing I2C devices
268 * that are present. This information is used to grow the drivermodel tree.
269 * For mainboards this is donestatically using i2c_register_board_info();
270 * bus numbers identify adapters thataren't yet available. For add-on boards,
271 * i2c_new_device() does thisdynamically with the adapter already known.
272 */
273struct i2c_board_info {
274 char type[I2C_NAME_SIZE];
275 unsigned short flags;
276 unsigned short addr;
277 void *platform_data;
278 struct dev_archdata *archdata;
279 struct device_node *of_node;
280 struct acpi_dev_node acpi_node;
281 int irq;
282};

从注释可以看到，i2c_board_info结构体用来保存I2C设备的相关信息，Linux根据这些信息创建I2C设备相关的设备模型树。对于mainboards，通过调用i2c_register_board_info()静态完成。对于add-on boards，通过调用i2c_new_device()动态完成。

i2c_board_info结构体有两个成员必须初始化，一个是type，用来初始化i2c_client.name；另一个是addr，用来初始化i2c_client.addr。其它i2c_board_info结构体成员根据需要赋值或保持为空。

宏I2C_BOARD_INFO定义在include/linux/i2c.h文件中，其内容如下：

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284/**
285 * I2C_BOARD_INFO - macro used to listan i2c device and its address
286 * @dev_type: identifies the device type
287 * @dev_addr: the device's address onthe bus.
288 *
289 * This macro initializes essentialfields of a struct i2c_board_info,
290 * declaring what has been provided on aparticular board. Optional
291 * fields (such as associated irq, ordevice-specific platform_data)
292 * are provided using conventionalsyntax.
293 */
294#define I2C_BOARD_INFO(dev_type,dev_addr) \
295 .type = dev_type, .addr = (dev_addr)

从注释可以看到，I2C_BOARD_INFO宏用来初始化i2c_board_info结构体的两个必须初始化的成员变量type和addr。i2c_board_info结构体的其它成员变量使用常规的初始化语法。

struct at24_platform_data定义在include/linux/i2c/at24.h文件中：

[cpp] view plain copy

4/**
15 * struct at24_platform_data - data toset up at24 (generic eeprom) driver
16 * @byte_len: size of eeprom in byte
17 * @page_size: number of byte which canbe written in one go
18 * @flags: tunable options, checkAT24_FLAG_* defines
19 * @setup: an optional callback invokedafter eeprom is probed; enables kernel
20 code to access eeprom via memory_accessor, see example
21 * @context: optional parameter passed tosetup()
22 *
23 * If you set up a custom eeprom type,please double-check the parameters.
24 * Especially page_size needs extra care,as you risk data loss if your value
25 * is bigger than what the chip actuallysupports!
26 *
27 * An example in pseudo code for asetup() callback:
28 *
29 * void get_mac_addr(structmemory_accessor *mem_acc, void *context)
30 * {
31 * u8 *mac_addr = ethernet_pdata->mac_addr;
32 * off_t offset = context;
33 *
34 * // Read MAC addr from EEPROM
35 * if (mem_acc->read(mem_acc, mac_addr, offset, ETH_ALEN) == ETH_ALEN)
36 * pr_info("Read MAC addr from EEPROM: %pM\n", mac_addr);
37 * }
38 *
39 * This function pointer and context cannow be set up in at24_platform_data.
40 */
41
42struct at24_platform_data {
43 u32 byte_len; /* size (sum of all addr) */
44 u16 page_size; /* for writes */
45 u8 flags;
46#define AT24_FLAG_ADDR16 0x80 /* address pointer is 16 bit */
47#define AT24_FLAG_READONLY 0x40 /* sysfs-entry will be read-only */
48#define AT24_FLAG_IRUGO 0x20 /* sysfs-entry will be world-readable */
49#define AT24_FLAG_TAKE8ADDR 0x10 /* take always 8 addresses (24c00) */
50
51 void (*setup)(structmemory_accessor *, void *context);
52 void *context;
53};

该结构体用来保存at24系列EEPROM的platform data。byte_len成员变量保存EEPROM的大小，以byte为单位。page_size成员变量用来指定一次最多能写多少个byte。对于Mini2440，定义at24_platform_data结构体变量at24c08：

[cpp] view plain copy

488static struct at24_platform_data at24c08= {
489 .byte_len = SZ_8K / 8,
490 .page_size = 16,
491};

SZ_8K宏即8K，定义在include/linux/sizes.h文件中：

[cpp] view plain copy

25#define SZ_8K 0x00002000

步骤2：调用i2c_register_board_info注册i2c设备相关信息

对于Mini2440的I2C设备at24c08 EEPROM，由arch/arm/mach-s3c24xx/mach-mini2440.c文件中的mini2440_init函数调用i2c_register_board_info注册i2c设备相关信息，mini2440_init函数内容如下：

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622static void __init mini2440_init(void)
623{
624 struct mini2440_features_t features = { 0 };
625 int i;
626
627 printk(KERN_INFO "MINI2440: Option string mini2440=%s\n",
628 mini2440_features_str);
629
630 /* Parse the feature string */
631 mini2440_parse_features(&features, mini2440_features_str);
632
633 /* turn LCD on */
634 s3c_gpio_cfgpin(S3C2410_GPC(0), S3C2410_GPC0_LEND);
635
636 /* Turn the backlight early on */
637 WARN_ON(gpio_request_one(S3C2410_GPG(4), GPIOF_OUT_INIT_HIGH, NULL));
638 gpio_free(S3C2410_GPG(4));
639
640 /* remove pullup on optional PWM backlight -- unused on 3.5 and 7"s*/
641 gpio_request_one(S3C2410_GPB(1), GPIOF_IN, NULL);
642 s3c_gpio_setpull(S3C2410_GPB(1), S3C_GPIO_PULL_UP);
643 gpio_free(S3C2410_GPB(1));
644
645 /* mark the key as input, without pullups (there is one on the board) */
646 for (i = 0; i < ARRAY_SIZE(mini2440_buttons); i++) {
647 s3c_gpio_setpull(mini2440_buttons[i].gpio, S3C_GPIO_PULL_UP);
648 s3c_gpio_cfgpin(mini2440_buttons[i].gpio, S3C2410_GPIO_INPUT);
649 }
650 if (features.lcd_index != -1) {
651 int li;
652
653 mini2440_fb_info.displays =
654 &mini2440_lcd_cfg[features.lcd_index];
655
656 printk(KERN_INFO "MINI2440: LCD");
657 for (li = 0; li < ARRAY_SIZE(mini2440_lcd_cfg); li++)
658 if (li == features.lcd_index)
659 printk(" [%d:%dx%d]",li,
660 mini2440_lcd_cfg[li].width,
661 mini2440_lcd_cfg[li].height);
662 else
663 printk(" %d:%dx%d",li,
664 mini2440_lcd_cfg[li].width,
665 mini2440_lcd_cfg[li].height);
666 printk("\n");
667 s3c24xx_fb_set_platdata(&mini2440_fb_info);
668 }
669
670 s3c24xx_udc_set_platdata(&mini2440_udc_cfg);
671 s3c24xx_mci_set_platdata(&mini2440_mmc_cfg);
672 s3c_nand_set_platdata(&mini2440_nand_info);
673 s3c_i2c0_set_platdata(NULL);
674
675 i2c_register_board_info(0, mini2440_i2c_devs,
676 ARRAY_SIZE(mini2440_i2c_devs));
677
678 platform_add_devices(mini2440_devices, ARRAY_SIZE(mini2440_devices));
679
680 if (features.count) /* the optional features */
681 platform_add_devices(features.optional, features.count);
682
683}

这个函数我们这里只需要关注675行，调用i2c_register_board_info注册mini2440_i2c_devs。mini2440_i2c_devs就是上面定义的i2c_board_info结构体数组，其中定义了at24c08相关信息。

i2c_register_board_info函数定义在drivers/i2c/i2c-boardinfo.c文件中，其内容如下：

[cpp] view plain copy

42/**
43 * i2c_register_board_info - staticallydeclare I2C devices
44 * @busnum: identifies the bus to whichthese devices belong
45 * @info: vector of i2c devicedescriptors
46 * @len: how many descriptors in the vector;may be zero to reserve
47 * the specified bus number.
48 *
49 * Systems using the Linux I2C driverstack can declare tables of board info
50 * while they initialize. This should be done in board-specific initcode
51 * near arch_initcall() time, orequivalent, before any I2C adapter driver is
52 * registered. For example, mainboard init code could defineseveral devices,
53 * as could the init code for eachdaughtercard in a board stack.
54 *
55 * The I2C devices will be created later,after the adapter for the relevant
56 * bus has been registered. After that moment, standard driver modeltools
57 * are used to bind "new style"I2C drivers to the devices. The busnumber
58 * for any device declared using thisroutine is not available for dynamic
59 * allocation.
60 *
61 * The board info passed can safely be__initdata, but be careful of embedded
62 * pointers (for platform_data,functions, etc) since that won't be copied.
63 */
64int __init
65i2c_register_board_info(int busnum,
66 struct i2c_board_info const *info, unsigned len)
67{
68 int status;
69
70 down_write(&__i2c_board_lock);
71
72 /* dynamic bus numbers will be assigned after the last static one */
73 if (busnum >= __i2c_first_dynamic_bus_num)
74 __i2c_first_dynamic_bus_num = busnum + 1;
75
76 for (status = 0; len; len--, info++) {
77 struct i2c_devinfo *devinfo;
78
79 devinfo = kzalloc(sizeof(*devinfo), GFP_KERNEL);
80 if (!devinfo) {
81 pr_debug("i2c-core: can'tregister boardinfo!\n");
82 status = -ENOMEM;
83 break;
84 }
85
86 devinfo->busnum = busnum;
87 devinfo->board_info = *info;
88 list_add_tail(&devinfo->list, &__i2c_board_list);
89 }
90
91 up_write(&__i2c_board_lock);
92
93 return status;
94}

第一个参数busnum表明I2C设备所依附的I2C总线的总线号。

72-74行，如果参数传递进来的busnum 大于等于__i2c_first_dynamic_bus_num，则将__i2c_first_dynamic_bus_num设置为busnum+1。__i2c_first_dynamic_bus_num代表第一个动态分配的I2C总线号，所以，动态分配的I2C总线号总是大于静态分配的I2C总线号。

__i2c_first_dynamic_bus_num定义在drivers/i2c/i2c-boardinfo.c文件中：

[cpp] view plain copy

38int __i2c_first_dynamic_bus_num;

因为__i2c_first_dynamic_bus_num是一个全局变量，所以其值被自动初始化为0。所以73行的if判断是成立的。

76-89行，循环遍历info数组，用i2c_board_info变量初始化structi2c_devinfo指针变量devinfo，然后将devinfo放入__i2c_board_list链表中。

i2c_devinfo变量定义在drivers/i2c/i2c-core.h文件中：

[cpp] view plain copy

22struct i2c_devinfo {
23 struct list_head list;
24 int busnum;
25 struct i2c_board_info board_info;
26};

可以看到i2c_devinfo结构体只有三个成员变量，busnum用来保存I2C设备所依附的I2C总线号。board_info用来保存I2C设备相关信息。list用于链接到全局链表__i2c_board_list中。

__i2c_board_list 链表定义在drivers/i2c/i2c-boardinfo.c文件中：

[cpp] view plain copy

35LIST_HEAD(__i2c_board_list);
36EXPORT_SYMBOL_GPL(__i2c_board_list);

全局变量__i2c_board_list上挂载着所有的I2C设备的信息，包括I2C设备所在的I2C总线的总线号。

所以，i2c_register_board_info函数并没有创建i2c_client，只是将i2c_devinfo变量放入__i2c_board_list链表中。那么，什么时候才会创建i2c_client呢？这个就与创建I2C设备驱动程序无关了，而是跟I2C adapter驱动程序有关：

注册一个I2C adapter有两种方法，一是调用i2c_add_adapter函数，二是调用i2c_add_numbered_adapter函数。

先来看i2c_add_adapter函数，它定义在drivers/i2c/i2c-core.c文件中：

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1099/**
1100 * i2c_add_adapter - declare i2cadapter, use dynamic bus number
1101 * @adapter: the adapter to add
1102 * Context: can sleep
1103 *
1104 * This routine is used to declare anI2C adapter when its bus number
1105 * doesn't matter or when its busnumber is specified by an dt alias.
1106 * Examples of bases when the busnumber doesn't matter: I2C adapters
1107 * dynamically added by USB links orPCI plugin cards.
1108 *
1109 * When this returns zero, a new busnumber was allocated and stored
1110 * in adap->nr, and the specifiedadapter became available for clients.
1111 * Otherwise, a negative errno value isreturned.
1112 */
1113int i2c_add_adapter(struct i2c_adapter*adapter)
1114{
1115 struct device *dev = &adapter->dev;
1116 int id;
1117
1118 if (dev->of_node) {
1119 id = of_alias_get_id(dev->of_node, "i2c");
1120 if (id >= 0) {
1121 adapter->nr = id;
1122 return__i2c_add_numbered_adapter(adapter);
1123 }
1124 }
1125
1126 mutex_lock(&core_lock);
1127 id = idr_alloc(&i2c_adapter_idr, adapter,
1128 __i2c_first_dynamic_bus_num, 0,GFP_KERNEL);
1129 mutex_unlock(&core_lock);
1130 if (id < 0)
1131 return id;
1132
1133 adapter->nr = id;
1134
1135 return i2c_register_adapter(adapter);
1136}

该函数为参数指定的i2c_adapter动态分配的个I2C总线号，并注册该i2c_adapter。

1118-1124行，忽略。

1127-1133行，调用idr_alloc，动态分配一个id号，并将该id号做为i2c_adapter的I2C总线号。

关于idr机制，我们不详细分析，只需要知道它是一种快速索引机制，它将一个整数ID与一个需要被索引的指针建立联系，方便进行查找。例如，这里idr_alloc返回的id与i2c_adapter建立了索引。idr_alloc的第三个参数指定返回ID的最小值（闭区间），第四个参数指定返回ID的最大值（开区间），即idr_alloc返回的ID大于等于第三个参数，而且必须小于第四个参数。在这个函数中，第三个参数为__i2c_first_dynamic_bus_num，所以返回的id必然是大于等于__i2c_first_dynamic_bus_num的，即动态分配的I2C总线号必然大于__i2c_first_dynamic_bus_num。

1135行，调用i2c_register_adapter注册i2c_adapter。

下面我们来看i2c_add_numbered_adapter，该函数定义在drivers/i2c/i2c-core.c文件中：

[cpp] view plain copy

1139/**
1140 * i2c_add_numbered_adapter - declarei2c adapter, use static bus number
1141 * @adap: the adapter to register (withadap->nr initialized)
1142 * Context: can sleep
1143 *
1144 * This routine is used to declare anI2C adapter when its bus number
1145 * matters. For example, use it for I2C adapters fromsystem-on-chip CPUs,
1146 * or otherwise built in to thesystem's mainboard, and where i2c_board_info
1147 * is used to properly configure I2Cdevices.
1148 *
1149 * If the requested bus number is setto -1, then this function will behave
1150 * identically to i2c_add_adapter, andwill dynamically assign a bus number.
1151 *
1152 * If no devices have pre-been declaredfor this bus, then be sure to
1153 * register the adapter before anydynamically allocated ones. Otherwise
1154 * the required bus ID may not beavailable.
1155 *
1156 * When this returns zero, thespecified adapter became available for
1157 * clients using the bus numberprovided in adap->nr. Also, the table
1158 * of I2C devices pre-declared usingi2c_register_board_info() is scanned,
1159 * and the appropriate driver modeldevice nodes are created. Otherwise, a
1160 * negative errno value is returned.
1161 */
1162int i2c_add_numbered_adapter(structi2c_adapter *adap)
1163{
1164 if (adap->nr == -1) /* -1 means dynamically assign bus id */
1165 return i2c_add_adapter(adap);
1166
1167 return __i2c_add_numbered_adapter(adap);
1168}

该函数用于注册参数指定的i2c_adapter，该i2c_adapter的I2C总线号即i2c_adapter.nr必须已经静态设置好了。如果adap->nr为-1，则调用i2c_add_adapter动态分配I2C总线号，再注册。否则，调用__i2c_add_numbered_adapter函数。

__i2c_add_numbered_adapter函数定义在drivers/i2c/i2c-core.c文件中：

[cpp] view plain copy

1078/**
1079 * __i2c_add_numbered_adapter -i2c_add_numbered_adapter where nr is never -1
1080 * @adap: the adapter to register (withadap->nr initialized)
1081 * Context: can sleep
1082 *
1083 * See i2c_add_numbered_adapter() fordetails.
1084 */
1085static int__i2c_add_numbered_adapter(struct i2c_adapter *adap)
1086{
1087 int id;
1088
1089 mutex_lock(&core_lock);
1090 id = idr_alloc(&i2c_adapter_idr, adap, adap->nr, adap->nr + 1,
1091 GFP_KERNEL);
1092 mutex_unlock(&core_lock);
1093 if (id < 0)
1094 return id == -ENOSPC ? -EBUSY : id;
1095
1096 return i2c_register_adapter(adap);
1097}

1090-1091行，调用idr_alloc函数，建立idr索引关系。返回的id必须大于等于第三个参数adap->nr，同时必须小于第四个参数adap->nr+1，所以返回的id必然等于adap->nr，即静态指定的I2C总线号。

1096行，调用i2c_register_adapter注册i2c_adapter。

到这里，我们就知道了注册一个i2c_adapter可以调用i2c_add_numbered_adapter函数静态指定一个I2C总线号，也可以调用i2c_add_adapter函数动态分配一个I2C总线号。但是不论哪种方法，最后的注册工作都必须通过调用i2c_register_adapter函数完成。

i2c_register_adapter函数定义在drivers/i2c/i2c-core.c文件中，其内容如下：

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980staticint i2c_register_adapter(struct i2c_adapter *adap)
981{
982 int res = 0;
983
984 /* Can't register until after driver model init */
985 if (unlikely(WARN_ON(!i2c_bus_type.p))) {
986 res = -EAGAIN;
987 goto out_list;
988 }
989
990 /* Sanity checks */
991 if (unlikely(adap->name[0] == '\0')) {
992 pr_err("i2c-core: Attempt to register an adapter with "
993 "no name!\n");
994 return -EINVAL;
995 }
996 if (unlikely(!adap->algo)) {
997 pr_err("i2c-core: Attempt to register adapter '%s' with "
998 "no algo!\n",adap->name);
999 return -EINVAL;
1000 }
1001
1002 rt_mutex_init(&adap->bus_lock);
1003 mutex_init(&adap->userspace_clients_lock);
1004 INIT_LIST_HEAD(&adap->userspace_clients);
1005
1006 /* Set default timeout to 1 second if not already set */
1007 if (adap->timeout == 0)
1008 adap->timeout = HZ;
1009
1010 dev_set_name(&adap->dev, "i2c-%d", adap->nr);
1011 adap->dev.bus = &i2c_bus_type;
1012 adap->dev.type = &i2c_adapter_type;
1013 res = device_register(&adap->dev);
1014 if (res)
1015 goto out_list;
1016
1017 dev_dbg(&adap->dev, "adapter [%s] registered\n",adap->name);
1018
1019#ifdef CONFIG_I2C_COMPAT
1020 res = class_compat_create_link(i2c_adapter_compat_class,&adap->dev,
1021 adap->dev.parent);
1022 if (res)
1023 dev_warn(&adap->dev,
1024 "Failed to createcompatibility class link\n");
1025#endif
1026
1027 /* bus recovery specific initialization */
1028 if (adap->bus_recovery_info) {
1029 struct i2c_bus_recovery_info*bri = adap->bus_recovery_info;
1030
1031 if (!bri->recover_bus) {
1032 dev_err(&adap->dev, "Norecover_bus() found, not using recovery\n");
1033 adap->bus_recovery_info = NULL;
1034 goto exit_recovery;
1035 }
1036
1037 /* Generic GPIO recovery */
1038 if (bri->recover_bus == i2c_generic_gpio_recovery) {
1039 if(!gpio_is_valid(bri->scl_gpio)) {
1040 dev_err(&adap->dev,"Invalid SCL gpio, not using recovery\n");
1041 adap->bus_recovery_info =NULL;
1042 goto exit_recovery;
1043 }
1044
1045 if(gpio_is_valid(bri->sda_gpio))
1046 bri->get_sda =get_sda_gpio_value;
1047 else
1048 bri->get_sda = NULL;
1049
1050 bri->get_scl =get_scl_gpio_value;
1051 bri->set_scl =set_scl_gpio_value;
1052 } else if (!bri->set_scl || !bri->get_scl) {
1053 /* Generic SCL recovery */
1054 dev_err(&adap->dev, "No{get|set}_gpio() found, not using recovery\n");
1055 adap->bus_recovery_info = NULL;
1056 }
1057 }
1058
1059exit_recovery:
1060 /* create pre-declared device nodes */
1061 if (adap->nr < __i2c_first_dynamic_bus_num)
1062 i2c_scan_static_board_info(adap);
1063
1064 /* Notify drivers */
1065 mutex_lock(&core_lock);
1066 bus_for_each_drv(&i2c_bus_type, NULL, adap, __process_new_adapter);
1067 mutex_unlock(&core_lock);
1068
1069 return 0;
1070
1071out_list:
1072 mutex_lock(&core_lock);
1073 idr_remove(&i2c_adapter_idr, adap->nr);
1074 mutex_unlock(&core_lock);
1075 return res;
1076}

984-1000行，做一些必要的检查工作。

1002-1008行，做一些简单的i2c_adapter成员变量初始化工作。

1010-1013行，初始化i2c_adapter.dev，并调用device_register注册i2c_adapter.dev。

1028-1057行，I2C总线恢复时相关的初始化工作。

1060-1062行，因为动态分析的I2C总线号必须大于或等于__i2c_first_dynamic_bus_num，所以，如果adap->nr< __i2c_first_dynamic_bus_num，说明是静态指定的I2C总线号，此时，要调用i2c_scan_static_board_info函数探测I2C总线上静态注册的I2C设备。

i2c_scan_static_board_info函数定义在drivers/i2c/i2c-core.c文件中，其内容如下：

[cpp] view plain copy

941staticvoid i2c_scan_static_board_info(struct i2c_adapter *adapter)
942{
943 struct i2c_devinfo *devinfo;
944
945 down_read(&__i2c_board_lock);
946 list_for_each_entry(devinfo, &__i2c_board_list, list) {
947 if (devinfo->busnum == adapter->nr
948 &&!i2c_new_device(adapter,
949 &devinfo->board_info))
950 dev_err(&adapter->dev,
951 "Can't create device at0x%02x\n",
952 devinfo->board_info.addr);
953 }
954 up_read(&__i2c_board_lock);
955}

946-953行，遍历__i2c_board_list链表，如果devinfo->busnum等于adapter->nr，即链表节点所代表的I2C设备的I2C总线号等于i2c_adapter的I2C总线号，则调用i2c_new_device创建并注册I2C设备对应的i2c_client结构体。

到这里，就和我们在本文开始部分介绍的静态注册的i2c_board_info信息联系起来了。回忆一下我们通过调用i2c_register_board_info函数将将包含所有I2C设备的i2c_board_info信息的i2c_devinfo变量加入到__i2c_board_list链表中。现在在注册i2c_adater时，又通过调用i2c_scan_static_board_info函数遍历__i2c_board_list链表，查找属于对应i2c_adapter的I2C设备，如果找到，调用i2c_new_device创建对应的i2c_client结构体。

i2c_new_device函数定义在drivers/i2c/i2c-core.c文件中，其内容如下：

[cpp] view plain copy

612/**
613* i2c_new_device - instantiate an i2c device
614* @adap: the adapter managing the device
615* @info: describes one I2C device; bus_num is ignored
616* Context: can sleep
617*
618* Create an i2c device. Binding is handled through driver model
619* probe()/remove() methods. A driver maybe bound to this device when we
620* return from this function, or any later moment (e.g. maybe hotplugging will
621* load the driver module). This call isnot appropriate for use by mainboard
622* initialization logic, which usually runs during an arch_initcall() long
623* before any i2c_adapter could exist.
624*
625* This returns the new i2c client, which may be saved for later use with
626* i2c_unregister_device(); or NULL to indicate an error.
627*/
628struct i2c_client *
629i2c_new_device(struct i2c_adapter *adap,struct i2c_board_info const *info)
630{
631 struct i2c_client *client;
632 int status;
633
634 client = kzalloc(sizeof *client, GFP_KERNEL);
635 if (!client)
636 return NULL;
637
638 client->adapter = adap;
639
640 client->dev.platform_data = info->platform_data;
641
642 if (info->archdata)
643 client->dev.archdata = *info->archdata;
644
645 client->flags = info->flags;
646 client->addr = info->addr;
647 client->irq = info->irq;
648
649 strlcpy(client->name, info->type, sizeof(client->name));
650
651 /* Check for address validity */
652 status = i2c_check_client_addr_validity(client);
653 if (status) {
654 dev_err(&adap->dev,"Invalid %d-bit I2C address 0x%02hx\n",
655 client->flags & I2C_CLIENT_TEN ?10 : 7, client->addr);
656 goto out_err_silent;
657 }
658
659 /* Check for address business */
660 status = i2c_check_addr_busy(adap, client->addr);
661 if (status)
662 goto out_err;
663
664 client->dev.parent = &client->adapter->dev;
665 client->dev.bus = &i2c_bus_type;
666 client->dev.type = &i2c_client_type;
667 client->dev.of_node = info->of_node;
668 ACPI_HANDLE_SET(&client->dev, info->acpi_node.handle);
669
670 /* For 10-bit clients, add an arbitrary offset to avoid collisions */
671 dev_set_name(&client->dev, "%d-%04x",i2c_adapter_id(adap),
672 client->addr | ((client->flags & I2C_CLIENT_TEN)
673 ? 0xa000 : 0));
674 status =device_register(&client->dev);
675 if (status)
676 goto out_err;
677
678 dev_dbg(&adap->dev, "client [%s] registered with bus id%s\n",
679 client->name, dev_name(&client->dev));
680
681 return client;
682
683out_err:
684 dev_err(&adap->dev, "Failed to register i2c client %s at0x%02x "
685 "(%d)\n", client->name, client->addr, status);
686out_err_silent:
687 kfree(client);
688 return NULL;