第一个驱动程序之i2c驱动架构介绍
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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:
200/**201 * struct i2c_client - represent an I2Cslave device202 * @flags: I2C_CLIENT_TEN indicates thedevice uses a ten bit chip address;203 * I2C_CLIENT_PEC indicates it uses SMBus Packet Error Checking204 * @addr: Address used on the I2C busconnected to the parent adapter.205 * @name: Indicates the type of thedevice, usually a chip name that's206 * generic enough to hide second-sourcing and compatible revisions.207 * @adapter: manages the bus segmenthosting this I2C device208 * @driver: device's driver, hencepointer to access routines209 * @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's212 * userspace_devices list213 *214 * An i2c_client identifies a singledevice (i.e. chip) connected to an215 * i2c bus. The behaviour exposed to Linuxis defined by the driver216 * 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:
485/*486 * I2C devices487 */488static struct at24_platform_data at24c08= {489 .byte_len = SZ_8K / 8,490 .page_size = 16,491};492493static 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:
251/**252 * struct i2c_board_info - template fordevice creation253 * @type: chip type, to initializei2c_client.name254 * @flags: to initializei2c_client.flags255 * @addr: stored in i2c_client.addr256 * @platform_data: stored ini2c_client.dev.platform_data257 * @archdata: copied intoi2c_client.dev.archdata258 * @of_node: pointer to OpenFirmwaredevice node259 * @acpi_node: ACPI device node260 * @irq: stored in i2c_client.irq261 *262 * I2C doesn't actually support hardwareprobing, although controllers and263 * devices may be able to useI2C_SMBUS_QUICK to tell whether or not there's264 * a device at a given address. Drivers commonly need more information than265 * that, such as chip type,configuration, associated IRQ, and so on.266 *267 * i2c_board_info is used to buildtables of information listing I2C devices268 * 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:
284/**285 * I2C_BOARD_INFO - macro used to listan i2c device and its address286 * @dev_type: identifies the device type287 * @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. Optional291 * 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:
4/**15 * struct at24_platform_data - data toset up at24 (generic eeprom) driver16 * @byte_len: size of eeprom in byte17 * @page_size: number of byte which canbe written in one go18 * @flags: tunable options, checkAT24_FLAG_* defines19 * @setup: an optional callback invokedafter eeprom is probed; enables kernel20 code to access eeprom via memory_accessor, see example21 * @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 value25 * 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 EEPROM35 * 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 */4142struct 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) */5051 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:
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:
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:
622static void __init mini2440_init(void)623{624 struct mini2440_features_t features = { 0 };625 int i;626627 printk(KERN_INFO "MINI2440: Option string mini2440=%s\n",628 mini2440_features_str);629630 /* Parse the feature string */631 mini2440_parse_features(&features, mini2440_features_str);632633 /* turn LCD on */634 s3c_gpio_cfgpin(S3C2410_GPC(0), S3C2410_GPC0_LEND);635636 /* 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));639640 /* 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));644645 /* 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;652653 mini2440_fb_info.displays =654 &mini2440_lcd_cfg[features.lcd_index];655656 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 else663 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 }669670 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);674675 i2c_register_board_info(0, mini2440_i2c_devs,676 ARRAY_SIZE(mini2440_i2c_devs));677678 platform_add_devices(mini2440_devices, ARRAY_SIZE(mini2440_devices));679680 if (features.count) /* the optional features */681 platform_add_devices(features.optional, features.count);682683}
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:
42/**43 * i2c_register_board_info - staticallydeclare I2C devices44 * @busnum: identifies the bus to whichthese devices belong45 * @info: vector of i2c devicedescriptors46 * @len: how many descriptors in the vector;may be zero to reserve47 * the specified bus number.48 *49 * Systems using the Linux I2C driverstack can declare tables of board info50 * while they initialize. This should be done in board-specific initcode51 * near arch_initcall() time, orequivalent, before any I2C adapter driver is52 * 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 relevant56 * bus has been registered. After that moment, standard driver modeltools57 * are used to bind "new style"I2C drivers to the devices. The busnumber58 * for any device declared using thisroutine is not available for dynamic59 * allocation.60 *61 * The board info passed can safely be__initdata, but be careful of embedded62 * pointers (for platform_data,functions, etc) since that won't be copied.63 */64int __init65i2c_register_board_info(int busnum,66 struct i2c_board_info const *info, unsigned len)67{68 int status;6970 down_write(&__i2c_board_lock);7172 /* 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;7576 for (status = 0; len; len--, info++) {77 struct i2c_devinfo *devinfo;7879 devinfo = kzalloc(sizeof(*devinfo), GFP_KERNEL);80 if (!devinfo) {81 pr_debug("i2c-core: can'tregister boardinfo!\n");82 status = -ENOMEM;83 break;84 }8586 devinfo->busnum = busnum;87 devinfo->board_info = *info;88 list_add_tail(&devinfo->list, &__i2c_board_list);89 }9091 up_write(&__i2c_board_lock);9293 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:
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:
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:
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:
1099/**1100 * i2c_add_adapter - declare i2cadapter, use dynamic bus number1101 * @adapter: the adapter to add1102 * Context: can sleep1103 *1104 * This routine is used to declare anI2C adapter when its bus number1105 * doesn't matter or when its busnumber is specified by an dt alias.1106 * Examples of bases when the busnumber doesn't matter: I2C adapters1107 * dynamically added by USB links orPCI plugin cards.1108 *1109 * When this returns zero, a new busnumber was allocated and stored1110 * 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;11171118 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 }11251126 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;11321133 adapter->nr = id;11341135 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:
1139/**1140 * i2c_add_numbered_adapter - declarei2c adapter, use static bus number1141 * @adap: the adapter to register (withadap->nr initialized)1142 * Context: can sleep1143 *1144 * This routine is used to declare anI2C adapter when its bus number1145 * 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_info1147 * is used to properly configure I2Cdevices.1148 *1149 * If the requested bus number is setto -1, then this function will behave1150 * 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 to1153 * register the adapter before anydynamically allocated ones. Otherwise1154 * the required bus ID may not beavailable.1155 *1156 * When this returns zero, thespecified adapter became available for1157 * clients using the bus numberprovided in adap->nr. Also, the table1158 * of I2C devices pre-declared usingi2c_register_board_info() is scanned,1159 * and the appropriate driver modeldevice nodes are created. Otherwise, a1160 * 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);11661167 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:
1078/**1079 * __i2c_add_numbered_adapter -i2c_add_numbered_adapter where nr is never -11080 * @adap: the adapter to register (withadap->nr initialized)1081 * Context: can sleep1082 *1083 * See i2c_add_numbered_adapter() fordetails.1084 */1085static int__i2c_add_numbered_adapter(struct i2c_adapter *adap)1086{1087 int id;10881089 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;10951096 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:
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 }10011002 rt_mutex_init(&adap->bus_lock);1003 mutex_init(&adap->userspace_clients_lock);1004 INIT_LIST_HEAD(&adap->userspace_clients);10051006 /* Set default timeout to 1 second if not already set */1007 if (adap->timeout == 0)1008 adap->timeout = HZ;10091010 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;10161017 dev_dbg(&adap->dev, "adapter [%s] registered\n",adap->name);10181019#ifdef CONFIG_I2C_COMPAT1020 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#endif10261027 /* bus recovery specific initialization */1028 if (adap->bus_recovery_info) {1029 struct i2c_bus_recovery_info*bri = adap->bus_recovery_info;10301031 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 }10361037 /* 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 }10441045 if(gpio_is_valid(bri->sda_gpio))1046 bri->get_sda =get_sda_gpio_value;1047 else1048 bri->get_sda = NULL;10491050 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 }10581059exit_recovery:1060 /* create pre-declared device nodes */1061 if (adap->nr < __i2c_first_dynamic_bus_num)1062 i2c_scan_static_board_info(adap);10631064 /* 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);10681069 return 0;10701071out_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:
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:
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; 689}
这个函数根据参数传递进来的信息,创建并注册i2c_client。
634行,为i2c_client变量分配内存空间。
638行,将i2c_client.adapter设置为参数传递进来的i2c_adapter。
640 行,将i2c_client.dev.platform_data设置为 info->platform_data;
645行,将i2c_client.flags设置为info->flags;
646行,将i2c_client.addr设置为info->addr;
647行,将i2c_client.irq设置为info->irq;
649行,将i2c_client.name设置为info->type;
651-657行,检查指定的I2C设备地址是否有效。
660-662行,检查指定的I2C设备地址是否忙。
664-674行,初始化i2c_client.dev,并调用device_register注册i2c_client.dev。
i2c_register_adapter函数我们还有一点内容没有分析完,回到i2c_register_adapter函数,上面我们分析到了1062行的i2c_scan_static_board_info(adap),只有在adap->nr小于__i2c_first_dynamic_bus_num即静态指定了i2c_adapter的I2C总线号的情况下,才会调用这个函数。对于动态分配I2C总线号的情况,直接跳过。这就说明,只有在静态指定i2c_adapter的I2C总线号的情况下,才会扫描静态注册的I2C设备,如果动态指定i2c_adapter的I2C总线号,不会扫描静态注册的I2C设备。对于I2C驱动程序,这种静态注册的方式,称为new-style driver;而动态探测的方式,称为legacy driver。
下面我们继续分析i2c_register_adapter函数,前面调用i2c_scan_static_board_info实例化了静态注册的I2C设备,下面要完成对I2C设备的动态探测和实例化:
不论是静态指定还是动态分配I2C总线号,都会调用到1066行的bus_for_each_drv函数。
1066行,调用bus_for_each_drv函数,该函数定义在drivers/base/bus.c文件中,其内容如下:
417/** 418 * bus_for_each_drv - driver iterator 419 * @bus: bus we're dealing with. 420 * @start: driver to start iterating on. 421 * @data: data to pass to the callback. 422 * @fn: function to call for each driver. 423 * 424 * This is nearly identical to the device iterator above. 425 * We iterate over each driver that belongs to @bus, and call 426 * @fn for each. If @fn returns anything but 0, we break out 427 * and return it. If @start is not NULL, we use it as the head 428 * of the list. 429 * 430 * NOTE: we don't return the driver that returns a non-zero 431 * value, nor do we leave the reference count incremented for that 432 * driver. If the caller needs to know that info, it must set it 433 * in the callback. It must also be sure to increment the refcount 434 * so it doesn't disappear before returning to the caller. 435 */ 436int bus_for_each_drv(struct bus_type *bus, struct device_driver *start, 437 void *data, int (*fn)(struct device_driver *, void *)) 438{ 439 struct klist_iter i; 440 struct device_driver *drv; 441 int error = 0; 442 443 if (!bus) 444 return -EINVAL; 445 446 klist_iter_init_node(&bus->p->klist_drivers, &i, 447 start ? &start->p->knode_bus : NULL); 448 while ((drv = next_driver(&i)) && !error) 449 error = fn(drv, data); 450 klist_iter_exit(&i); 451 return error; 452}
这个函数我们在《Linux设备模型分析之device(基于3.10.1内核)》一文中已经分析过了。448-449行,这个while循环依次遍历bus->p->klist_drivers中的所有device_driver,对于每个device_driver,调用fn(drv,data)函数。这里,传递过来的fn参数是__process_new_adapter,data参数是adap。这个循环是一个关键点,注册一个新的i2c_adapter后,要为该i2c_adapter上的i2c设备匹配驱动程序,这个匹配过程就是通过这个循环调用__process_new_adapter函数完成的。
__process_new_adapter函数定义在drivers/i2c/i2c-core.c文件中,其内容如下:
975static int __process_new_adapter(struct device_driver *d, void *data) 976{ 977 return i2c_do_add_adapter(to_i2c_driver(d), data); 978}
注意i2c_do_add_adapter函数的第一个参数,从device_driver转换为i2c_driver。
i2c_do_add_adapter函数定义在drivers/i2c/i2c-core.c文件中,其内容如下:
957static int i2c_do_add_adapter(struct i2c_driver *driver, 958 struct i2c_adapter *adap) 959{ 960 /* Detect supported devices on that bus, and instantiate them */ 961 i2c_detect(adap, driver); 962 963 /* Let legacy drivers scan this bus for matching devices */ 964 if (driver->attach_adapter) { 965 dev_warn(&adap->dev, "%s: attach_adapter method is deprecated\n", 966 driver->driver.name); 967 dev_warn(&adap->dev, "Please use another way to instantiate " 968 "your i2c_client\n"); 969 /* We ignore the return code; if it fails, too bad */ 970 driver->attach_adapter(adap); 971 } 972 return 0; 973}
961行,调用i2c_detect函数,探测并初始化该i2c总线上的i2c设备。该函数定义在drivers/i2c/i2c-core.c文件中,其内容如下:
1730static int i2c_detect(struct i2c_adapter *adapter, struct i2c_driver *driver)1731{1732 const unsigned short *address_list;1733 struct i2c_client *temp_client;1734 int i, err = 0;1735 int adap_id = i2c_adapter_id(adapter);17361737 address_list = driver->address_list;1738 if (!driver->detect || !address_list)1739 return 0;17401741 /* Stop here if the classes do not match */1742 if (!(adapter->class & driver->class))1743 return 0;17441745 /* Set up a temporary client to help detect callback */1746 temp_client = kzalloc(sizeof(struct i2c_client), GFP_KERNEL);1747 if (!temp_client)1748 return -ENOMEM;1749 temp_client->adapter = adapter;17501751 for (i = 0; address_list[i] != I2C_CLIENT_END; i += 1) {1752 dev_dbg(&adapter->dev, "found normal entry for adapter %d, "1753 "addr 0x%02x\n", adap_id, address_list[i]);1754 temp_client->addr = address_list[i];1755 err = i2c_detect_address(temp_client, driver);1756 if (unlikely(err))1757 break;1758 }17591760 kfree(temp_client);1761 return err;1762}
1755行,调用i2c_detect_address,探测指定的地址上的I2C设备是否存在,如果存在,注册该i2c设备。i2c_detect_address函数定义在drivers/i2c/i2c-core.c文件中,其内容如下:
1675static int i2c_detect_address(struct i2c_client *temp_client,1676 struct i2c_driver *driver)1677{1678 struct i2c_board_info info;1679 struct i2c_adapter *adapter = temp_client->adapter;1680 int addr = temp_client->addr;1681 int err;16821683 /* Make sure the address is valid */1684 err = i2c_check_addr_validity(addr);1685 if (err) {1686 dev_warn(&adapter->dev, "Invalid probe address 0x%02x\n",1687 addr);1688 return err;1689 }16901691 /* Skip if already in use */1692 if (i2c_check_addr_busy(adapter, addr))1693 return 0;16941695 /* Make sure there is something at this address */1696 if (!i2c_default_probe(adapter, addr))1697 return 0;16981699 /* Finally call the custom detection function */1700 memset(&info, 0, sizeof(struct i2c_board_info));1701 info.addr = addr;1702 err = driver->detect(temp_client, &info);1703 if (err) {1704 /* -ENODEV is returned if the detection fails. We catch it1705 here as this isn't an error. */1706 return err == -ENODEV ? 0 : err;1707 }17081709 /* Consistency check */1710 if (info.type[0] == '\0') {1711 dev_err(&adapter->dev, "%s detection function provided "1712 "no name for 0x%x\n", driver->driver.name,1713 addr);1714 } else {1715 struct i2c_client *client;17161717 /* Detection succeeded, instantiate the device */1718 dev_dbg(&adapter->dev, "Creating %s at 0x%02x\n",1719 info.type, info.addr);1720 client = i2c_new_device(adapter, &info);1721 if (client)1722 list_add_tail(&client->detected, &driver->clients);1723 else1724 dev_err(&adapter->dev, "Failed creating %s at 0x%02x\n",1725 info.type, info.addr);1726 }1727 return 0;1728}
1702行,调用driver->detect。
1720行,如果探测到i2c设备确实存在,调用i2c_new_device函数初始化对应的i2c_client结构体并注册。i2c_new_device函数我们在前面已经分析过。
至此,i2c_adapter的注册过程我们就清楚了。同时,我们对I2C设备的注册定义和注册也就完全清楚了。
二、定义和注册I2C设备驱动
步骤1:定义i2c_driver结构体变量。
Linux I2C设备驱动程序对应的结构体是structi2c_driver,定义在include/linux/i2c.h文件中:
124/**125 * struct i2c_driver - represent an I2Cdevice driver126 * @class: What kind of i2c device weinstantiate (for detect)127 * @attach_adapter: Callback for busaddition (deprecated)128 * @probe: Callback for device binding129 * @remove: Callback for deviceunbinding130 * @shutdown: Callback for deviceshutdown131 * @suspend: Callback for device suspend132 * @resume: Callback for device resume133 * @alert: Alert callback, for examplefor the SMBus alert protocol134 * @command: Callback for bus-wide signaling(optional)135 * @driver: Device driver model driver136 * @id_table: List of I2C devicessupported by this driver137 * @detect: Callback for devicedetection138 * @address_list: The I2C addresses toprobe (for detect)139 * @clients: List of detected clients wecreated (for i2c-core use only)140 *141 * The driver.owner field should be setto the module owner of this driver.142 * The driver.name field should be setto the name of this driver.143 *144 * For automatic device detection, both @detectand @address_list must145 * be defined. @class should also beset, otherwise only devices forced146 * with module parameters will becreated. The detect function must147 * fill at least the name field of thei2c_board_info structure it is148 * handed upon successful detection, andpossibly also the flags field.149 *150 * If @detect is missing, the driverwill still work fine for enumerated151 * devices. Detected devices simplywon't be supported. This is expected152 * for the many I2C/SMBus devices whichcan't be detected reliably, and153 * the ones which can always beenumerated in practice.154 *155 * The i2c_client structure which ishanded to the @detect callback is156 * not a real i2c_client. It isinitialized just enough so that you can157 * call i2c_smbus_read_byte_data andfriends on it. Don't do anything158 * else with it. In particular, callingdev_dbg and friends on it is159 * not allowed.160 */161struct i2c_driver {162 unsigned int class;163164 /* Notifies the driver that a new bus has appeared. You should avoid165 * using this, it will be removed in a near future.166 */167 int (*attach_adapter)(struct i2c_adapter *) __deprecated;168169 /* Standard driver model interfaces */170 int (*probe)(struct i2c_client *, const struct i2c_device_id *);171 int (*remove)(struct i2c_client *);172173 /* driver model interfaces that don't relate to enumeration */174 void (*shutdown)(struct i2c_client *);175 int (*suspend)(struct i2c_client *, pm_message_t mesg);176 int (*resume)(struct i2c_client *);177178 /* Alert callback, for example for the SMBus alert protocol.179 * The format and meaning of the data value depends on the protocol.180 * For the SMBus alert protocol, there is a single bit of data passed181 * as the alert response's low bit ("event flag").182 */183 void (*alert)(struct i2c_client *, unsigned int data);184185 /* a ioctl like command that can be used to perform specific functions186 * with the device.187 */188 int (*command)(struct i2c_client *client, unsigned int cmd, void *arg);189190 struct device_driver driver;191 const struct i2c_device_id *id_table;192193 /* Device detection callback for automatic device creation */194 int (*detect)(struct i2c_client *, struct i2c_board_info *);195 const unsigned short *address_list;196 struct list_head clients;197};
注意注释中的说明,driver.name和driver.owner必须初始化。
id_table成员变量是i2c_device_id结构体指针,它用来保存该i2c_driver支持的I2C设备列表。
struct i2c_device_id定义在include/linux/mod_devicetable.h文件中,其内容如下:
419struct i2c_device_id {420 char name[I2C_NAME_SIZE];421 kernel_ulong_t driver_data; /* Data private to the driver */422};
对于Mini2440的I2C设备at24c08 EEPROM,其对应的i2c_driver结构体变量实现在drivers/misc/eeprom/at24.c文件中:
677static struct i2c_driver at24_driver = {678 .driver = {679 .name = "at24",680 .owner = THIS_MODULE,681 },682 .probe = at24_probe,683 .remove = at24_remove,684 .id_table = at24_ids,685};
678-681行,初始化了要求必须初始化的i2c_driver.driver.name和i2c_driver.driver.owner。
682行,指定i2c_driver.probe函数为at24_probe。
683行,指定i2c_driver.remove函数为at24_remove。
684行,指定i2c_driver.id_table为at24_ids。
at24_ids定义在drivers/misc/eeprom/at24.c文件中,其内容如下:
99#define AT24_SIZE_BYTELEN 5100#define AT24_SIZE_FLAGS 8101102#define AT24_BITMASK(x) (BIT(x) - 1)103104/* create non-zero magic value for giveneeprom parameters */105#define AT24_DEVICE_MAGIC(_len,_flags) \106 ((1 << AT24_SIZE_FLAGS | (_flags)) \107 << AT24_SIZE_BYTELEN | ilog2(_len))108109static const struct i2c_device_idat24_ids[] = {110 /* needs 8 addresses as A0-A2 are ignored */111 { "24c00", AT24_DEVICE_MAGIC(128 / 8, AT24_FLAG_TAKE8ADDR) },112 /* old variants can't be handled with this generic entry! */113 { "24c01", AT24_DEVICE_MAGIC(1024 / 8, 0) },114 { "24c02", AT24_DEVICE_MAGIC(2048 / 8, 0) },115 /* spd is a 24c02 in memory DIMMs */116 { "spd", AT24_DEVICE_MAGIC(2048 / 8,117 AT24_FLAG_READONLY | AT24_FLAG_IRUGO) },118 { "24c04", AT24_DEVICE_MAGIC(4096 / 8, 0) },119 /* 24rf08 quirk is handled at i2c-core */120 { "24c08", AT24_DEVICE_MAGIC(8192 / 8, 0) },121 { "24c16", AT24_DEVICE_MAGIC(16384 / 8, 0) },122 { "24c32", AT24_DEVICE_MAGIC(32768 / 8, AT24_FLAG_ADDR16) },123 { "24c64", AT24_DEVICE_MAGIC(65536 / 8, AT24_FLAG_ADDR16) },124 { "24c128", AT24_DEVICE_MAGIC(131072 / 8, AT24_FLAG_ADDR16) },125 { "24c256", AT24_DEVICE_MAGIC(262144 / 8, AT24_FLAG_ADDR16) },126 { "24c512", AT24_DEVICE_MAGIC(524288 / 8, AT24_FLAG_ADDR16) },127 { "24c1024", AT24_DEVICE_MAGIC(1048576 / 8, AT24_FLAG_ADDR16)},128 { "at24", 0 },129 { /* END OF LIST */ }130};
可以看到,at24_driver支持很多设备,其中包括Mini2440使用的24c08 EEPROM。
步骤2:调用i2c_add_driver注册i2c_driver结构体变量。
对于Mini2440的I2C设备at24c08 EEPROM,这一步工作是在drivers/misc/eeprom/at24.c文件中的at24_init函数中完成的:
687static int __init at24_init(void)688{689 if (!io_limit) {690 pr_err("at24: io_limit must not be 0!\n");691 return -EINVAL;692 }693694 io_limit = rounddown_pow_of_two(io_limit);695 return i2c_add_driver(&at24_driver);696}
695行,调用i2c_add_driver注册上面定义的at24_driver。
i2c_add_driver是一个宏,定义在include/linux/i2c.h文件中:
497/* use a define to avoid include chaining to get THIS_MODULE */498#define i2c_add_driver(driver) \499 i2c_register_driver(THIS_MODULE, driver)
i2c_register_driver函数定义在drivers/i2c/i2c-core.c文件中,其内容如下:
1307/*1308 * An i2c_driver is used with one or more i2c_client (device) nodes to access1309 * i2c slave chips, on a bus instance associated with some i2c_adapter.1310 */13111312int i2c_register_driver(struct module *owner, struct i2c_driver *driver)1313{1314 int res;13151316 /* Can't register until after driver model init */1317 if (unlikely(WARN_ON(!i2c_bus_type.p)))1318 return -EAGAIN;13191320 /* add the driver to the list of i2c drivers in the driver core */1321 driver->driver.owner = owner;1322 driver->driver.bus = &i2c_bus_type;13231324 /* When registration returns, the driver core1325 * will have called probe() for all matching-but-unbound devices.1326 */1327 res = driver_register(&driver->driver);1328 if (res)1329 return res;13301331 /* Drivers should switch to dev_pm_ops instead. */1332 if (driver->suspend)1333 pr_warn("i2c-core: driver [%s] using legacy suspend method\n",1334 driver->driver.name);1335 if (driver->resume)1336 pr_warn("i2c-core: driver [%s] using legacy resume method\n",1337 driver->driver.name);13381339 pr_debug("i2c-core: driver [%s] registered\n", driver->driver.name);13401341 INIT_LIST_HEAD(&driver->clients);1342 /* Walk the adapters that are already present */1343 i2c_for_each_dev(driver, __process_new_driver);13441345 return 0;1346}
1327行,调用driver_register注册i2c_driver.driver。参考《 Linux设备模型分析之device_driver(基于3.10.1内核)》对Linux设备模型的分析,在driver_register执行过程中,如果I2C总线上找到了与该驱动匹配的I2C设备,则i2c_driver.probe函数会被调用执行。
1343行,调用i2c_for_each_dev遍历所有已存在的i2c_adapter。该函数定义在drivers/i2c/i2c-core.c文件中,其内容如下:
1288int i2c_for_each_dev(void *data, int (*fn)(struct device *, void *))1289{1290 int res;12911292 mutex_lock(&core_lock);1293 res = bus_for_each_dev(&i2c_bus_type, NULL, data, fn);1294 mutex_unlock(&core_lock);12951296 return res;1297}
286intbus_for_each_dev(struct bus_type *bus, struct device *start, 287 void *data, int (*fn)(struct device *, void *)) 288{ 289 struct klist_iter i; 290 struct device *dev; 291 int error = 0; 292 293 if (!bus || !bus->p) 294 return -EINVAL; 295 296 klist_iter_init_node(&bus->p->klist_devices, &i, 297 (start ?&start->p->knode_bus : NULL)); 298 while ((dev = next_device(&i)) && !error) 299 error = fn(dev, data); 300 klist_iter_exit(&i); 301 return error; 302}
我们在《 Linux设备模型分析之device_driver(基于3.10.1内核)》一文中已经分析过这个函数。这里,传递过来的data参数是要注册的i2c_driver,fn参数是__process_new_driver函数,所以我们来看__process_new_driver函数,该函数定义在drivers/i2c/i2c-core.c文件中,其内容如下:
1300static int __process_new_driver(structdevice *dev, void *data)1301{1302 if (dev->type != &i2c_adapter_type)1303 return 0;1304 return i2c_do_add_adapter(data, to_i2c_adapter(dev));1305}
i2c_do_add_adapter函数定义在drivers/i2c/i2c-core.c文件中,其内容如下:
957static int i2c_do_add_adapter(structi2c_driver *driver, 958 struct i2c_adapter *adap) 959{ 960 /* Detect supported devices on that bus, and instantiate them */ 961 i2c_detect(adap, driver); 962 963 /* Let legacy drivers scan this bus for matching devices */ 964 if (driver->attach_adapter) { 965 dev_warn(&adap->dev, "%s: attach_adapter method isdeprecated\n", 966 driver->driver.name); 967 dev_warn(&adap->dev, "Please use another way to instantiate" 968 "your i2c_client\n"); 969 /* We ignore the return code; if it fails, too bad */ 970 driver->attach_adapter(adap); 971 } 972 return 0; 973}
这个函数我们在分析i2c_adapter的注册过程时已经分析过了,它主要完成i2c_driver与i2c_adapter上的i2c设备的匹配工作,如果匹配成功,初始化并注册对应的i2c_client。
至此,i2c_driver的注册过程我们就清楚了。
步骤3:实现i2c_driver中要示实现的函数
对于Mini2440的I2C设备at24c08 EEPROM,at24_driver要求实现的是i2c_driver.probe和i2c_driver.remove函数。
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