/******************************************************************************************* *                          I.MX6 Linux I2C device& driver hacking * 声明： *     1. 本文主要是对Linux I2C驱动进行代码跟踪，主要是为了能够对I2C驱动框架有个全面的了解； *     2. 本文源代码来自myzr_android4_2_2_1_1_0.tar.bz2； *     3. 如果你有兴趣，请尽量自己去对代码进行跟踪，这样自己会对I2C有一个框架结构上的理解； * *                                                2015-6-4 晴 深圳 南山平山村 曾剑锋 ******************************************************************************************/                     \\\\\\\\\\\\\\\\\-*- 目录 -*-/////                                       |   一、跟踪板级文件:                      |   二、跟踪mx6q_sabresd_i2c_data参数:                     |   三、跟踪imx6q_add_imx_i2c()函数:                     |   四、跟踪imx6q_imx_i2c_data参数:                     |   五、跟踪imx_add_imx_i2c()函数:                     |   六、跟踪mxc_i2c0_board_info参数:                     |   七、跟踪i2c_register_board_info()函数:                     |   八、I2C adapter(适配器)跟踪:                     |   九、I2C设备追踪:                     |   十、跟踪__process_new_driver参数:                     |   十一、跟踪i2c_for_each_dev()函数:                     |   十二、跟踪max6875_probe()函数:                     \\\\\\\\\\\\\\\\\\\\\\\///                                        一、跟踪板级文件:     1. cat arch/arm/mach-mx6/board-mx6q_sabresd.c        ......        /*         * initialize __mach_desc_MX6Q_SABRESD data structure.         */        MACHINE_START(MX6Q_SABRESD, "Freescale i.MX 6Quad/DualLite/Solo Sabre-SD Board")            /* Maintainer: Freescale Semiconductor, Inc. */            .boot_params = MX6_PHYS_OFFSET + 0x100,            .fixup = fixup_mxc_board,            .map_io = mx6_map_io,            .init_irq = mx6_init_irq,            .init_machine = mx6_sabresd_board_init,   //跟踪板级初始化函数            .timer = &mx6_sabresd_timer,            .reserve = mx6q_sabresd_reserve,        MACHINE_END    2. cat arch/arm/mach-mx6/board-mx6q_sabresd.c        ......        /*!         * Board specific initialization.         */        static void __init mx6_sabresd_board_init(void)        {            ......            /**             * 接下来我们需要向以下4个方向去跟踪代码:             *     1. 跟踪mx6q_sabresd_i2c_data参数;             *     2. 跟踪imx6q_add_imx_i2c()函数;             *     3. 跟踪mxc_i2c0_board_info参数,在里面继续跟踪wm8962_config_data,             *         因为下面这两行代码修改了mxc_i2c0_board_info第一个元素;             *     4. 跟踪i2c_register_board_info()函数;             */            strcpy(mxc_i2c0_board_info[0].type, "wm8962");                mxc_i2c0_board_info[0].platform_data = &wm8962_config_data;  //跟踪wm8962_config_data            /**             * 这里相当于注册I2C控制器             */            imx6q_add_imx_i2c(0, &mx6q_sabresd_i2c_data);   //跟踪参数,函数            imx6q_add_imx_i2c(1, &mx6q_sabresd_i2c_data);            imx6q_add_imx_i2c(2, &mx6q_sabresd_i2c_data);            /**             * 这里相当于注册I2C设备             */            i2c_register_board_info(0, mxc_i2c0_board_info, //跟踪参数,函数                    ARRAY_SIZE(mxc_i2c0_board_info));            i2c_register_board_info(1, mxc_i2c1_board_info,                    ARRAY_SIZE(mxc_i2c1_board_info));            i2c_register_board_info(2, mxc_i2c2_board_info,                    ARRAY_SIZE(mxc_i2c2_board_info));            ......        }        ......二、跟踪mx6q_sabresd_i2c_data参数:    1. cat arch/arm/mach-mx6/board-mx6q_sabresd.c        ......        static struct imxi2c_platform_data mx6q_sabresd_i2c_data = {  //跟踪结构体            .bitrate = 100000,        };        ......    2. cat arch/arm/plat-mxc/include/mach/i2c.h        ......        struct imxi2c_platform_data {            int (*init)(struct device *dev);            void (*exit)(struct device *dev);            int bitrate;        };        ......三、跟踪imx6q_add_imx_i2c()函数:    cat arch/arm/mach-mx6/devices-imx6q.h        ......        /**         * 这里需要跟踪2个方向:         *     1. 跟踪imx6q_imx_i2c_data参数;         *     2. 跟踪imx_add_imx_i2c()函数;         */        extern const struct imx_imx_i2c_data imx6q_imx_i2c_data[] __initconst;        #define imx6q_add_imx_i2c(id, pdata)    \            imx_add_imx_i2c(&imx6q_imx_i2c_data[id], pdata)   //跟踪结构体,函数        ......四、跟踪imx6q_imx_i2c_data参数:    1. cat arch/arm/plat-mxc/devices/platform-imx-i2c.c        ......        #ifdef CONFIG_SOC_IMX6Q        const struct imx_imx_i2c_data imx6q_imx_i2c_data[] __initconst = {        #define imx6q_imx_i2c_data_entry(_id, _hwid)                \            imx_imx_i2c_data_entry(MX6Q, _id, _hwid, SZ_4K)            imx6q_imx_i2c_data_entry(0, 1),     //跟踪这个宏            imx6q_imx_i2c_data_entry(1, 2),            imx6q_imx_i2c_data_entry(2, 3),        };        #endif /* ifdef CONFIG_SOC_IMX6Q */        ......    2. cat arch/arm/plat-mxc/include/mach/devices-common.h        ......        #include 
     
              struct imx_imx_i2c_data {            int id;            resource_size_t iobase;            resource_size_t iosize;            resource_size_t irq;        };        ......    3. cat arch/arm/plat-mxc/devices/platform-imx-i2c.c        ......        /**         *  1. 如果传入参数是:         *      1. soc = MX6Q;         *      2. _id = 0;         *      3. _hwid = 1;         *      4. size = SZ_4K;         *  2. .iobase = soc ## _I2C ## _hwid ## _BASE_ADDR合成结果:         *      .iobase = MX6Q_I2C1_BASE_ADDR = 0x021A0000 (看后面的跟踪代码推演计算)         *  3. .irq = soc ## _INT_I2C ## _hwid合成结果:         *      .irq = MX6Q_INT_I2C1 = 68          */        #define imx_imx_i2c_data_entry_single(soc, _id, _hwid, _size)        \            {                                \                .id = _id,                        \                .iobase = soc ## _I2C ## _hwid ## _BASE_ADDR,        \   //跟踪合成后的宏                .iosize = _size,                    \                .irq = soc ## _INT_I2C ## _hwid,            \            }        #define imx_imx_i2c_data_entry(soc, _id, _hwid, _size)            \            [_id] = imx_imx_i2c_data_entry_single(soc, _id, _hwid, _size)        ......    4. cat arch/arm/plat-mxc/include/mach/mx6.h        ......        /**         * 1. I2C1首地址推演计算:         *      MX6Q_I2C1_BASE_ADDR = (AIPS2_OFF_BASE_ADDR + 0x20000)         *      MX6Q_I2C1_BASE_ADDR = ((ATZ2_BASE_ADDR + 0x80000) + 0x20000)         *      MX6Q_I2C1_BASE_ADDR = ((AIPS2_ARB_BASE_ADDR + 0x80000) + 0x20000)         *      MX6Q_I2C1_BASE_ADDR = ((0x02100000 + 0x80000) + 0x20000)         *      MX6Q_I2C1_BASE_ADDR = (0x02100000 + 0x80000 + 0x20000)         *      MX6Q_I2C1_BASE_ADDR = (0x02100000 + 0x80000 + 0x20000)         *      MX6Q_I2C1_BASE_ADDR = 0x021A0000 (符合下面参考书给出的首地址)         * 2. 参考书IMX6DQRM_revC.pdf给出的I2C1的首地址:         *      -------------------------------------------------------------         *      | Start Address | End Address | Region | Allocation  | Size |         *      +---------------+-------------+--------+-------------+------+         *      |   021A_0000   |  021A_3FFF  | AIPS-2 |    I2C1     | 16KB |         *      -------------------------------------------------------------         */        #define MX6Q_I2C1_BASE_ADDR        (AIPS2_OFF_BASE_ADDR + 0x20000)        ......        /* ATZ#2- Off Platform */        #define AIPS2_OFF_BASE_ADDR        (ATZ2_BASE_ADDR + 0x80000)        ......        #define ATZ2_BASE_ADDR            AIPS2_ARB_BASE_ADDR        ......        #define AIPS2_ARB_BASE_ADDR        0x02100000        ......    5. cat arch/arm/plat-mxc/include/mach/mx6.h        ......        /**         *  1. 参考书IMX6DQRM_revC.pdf给出的I2C1的中断号:         *      ---------------------------------------------         *      |IRQ | Interrupt  | Interrupt Description   |         *      |    |  Source    |                         |         *      +----+------------+-------------------------+         *      |68  | ECSPI1I2C1 | I2C1 interrupt request. |         *      ---------------------------------------------         *  2. 非常精准的符合参好书  :)         */        #define MX6Q_INT_I2C1            68        ......五、跟踪imx_add_imx_i2c()函数:    1. cat arch/arm/plat-mxc/devices/platform-imx-i2c.c        ......        struct platform_device *__init imx_add_imx_i2c(                const struct imx_imx_i2c_data *data,                const struct imxi2c_platform_data *pdata)        {            //利用传入参数合成平台资源数据            struct resource res[] = {                {                    .start = data->iobase,                    .end = data->iobase + data->iosize - 1,                    .flags = IORESOURCE_MEM,                }, {                    .start = data->irq,                    .end = data->irq,                    .flags = IORESOURCE_IRQ,                },            };            /**             * 从这里可以知道设备匹配时候的名字，跟踪该函数             */            return imx_add_platform_device("imx-i2c", data->id,                    res, ARRAY_SIZE(res),                    pdata, sizeof(*pdata));                 }        ......    2. cat arch/arm/plat-mxc/include/mach/devices-common.h        ......        static inline struct platform_device *imx_add_platform_device(                const char *name, int id,                const struct resource *res, unsigned int num_resources,                const void *data, size_t size_data)        {            //跟踪该函数            return imx_add_platform_device_dmamask(                    name, id, res, num_resources, data, size_data, 0);        }        ......    3. cat arch/arm/plat-mxc/devices.c        ......        struct platform_device *__init imx_add_platform_device_dmamask(                const char *name, int id,                const struct resource *res, unsigned int num_resources,                const void *data, size_t size_data, u64 dmamask)        {            int ret = -ENOMEM;            struct platform_device *pdev;            pdev = platform_device_alloc(name, id);            if (!pdev)                goto err;            ......            if (res) {                ret = platform_device_add_resources(pdev, res, num_resources);                if (ret)                    goto err;            }            if (data) {                ret = platform_device_add_data(pdev, data, size_data);                if (ret)                    goto err;            }            ret = platform_device_add(pdev);    //设备注册            if (ret) {        err:                if (dmamask)                    kfree(pdev->dev.dma_mask);                platform_device_put(pdev);                return ERR_PTR(ret);            }            return pdev;        }        ......六、跟踪mxc_i2c0_board_info参数:    1. cat arch/arm/mach-mx6/board-mx6q_sabresd.c        ......        static struct i2c_board_info mxc_i2c0_board_info[] __initdata = {  //跟踪结构体            /**             * 这是板级初始化函数中的另一部分:             *  strcpy(mxc_i2c0_board_info[0].type, "wm8962");             *      mxc_i2c0_board_info[0].platform_data = &wm8962_config_data;  //跟踪目标wm8962_config_data             *             *  通过这里可以知道wm8962的I2C地址是:0x1a             */            {                I2C_BOARD_INFO("wm89**", 0x1a),            },            {                I2C_BOARD_INFO("ov564x", 0x3c),                .platform_data = (void *)&camera_data,            },            {                I2C_BOARD_INFO("mma8451", 0x1d),                .platform_data = (void *)&mma8451_position,            },            {                I2C_BOARD_INFO("isl1208", 0x6f),            },        };        ......    2. cat include/linux/i2c.h        ......        struct i2c_board_info {            char        type[I2C_NAME_SIZE];            unsigned short    flags;            unsigned short    addr;            void        *platform_data;            struct dev_archdata    *archdata;            struct device_node *of_node;            int        irq;        };        ......    3. cat arch/arm/mach-mx6/board-mx6q_sabresd.c        ......        static struct wm8962_pdata wm8962_config_data = { //跟踪结构体            .gpio_init = {                [2] = WM8962_GPIO_FN_DMICCLK,                [4] = 0x8000 | WM8962_GPIO_FN_DMICDAT,            },        };        ......    4. cat include/sound/wm8962.h        ......        struct wm8962_pdata {            int gpio_base;            u32 gpio_init[WM8962_MAX_GPIO];            /* Setup for microphone detection, raw value to be written to             * R48(0x30) - only microphone related bits will be updated.             * Detection may be enabled here for use with signals brought             * out on the GPIOs. */            u32 mic_cfg;            bool irq_active_low;            bool spk_mono;   /* Speaker outputs tied together as mono */        };        ......七、跟踪i2c_register_board_info()函数:    1. cat drivers/i2c/i2c-boardinfo.c        ......        int __init i2c_register_board_info(int busnum,            struct i2c_board_info const *info, unsigned len)        {            int status;            down_write(&__i2c_board_lock);            /* dynamic bus numbers will be assigned after the last static one */            if (busnum >= __i2c_first_dynamic_bus_num)                __i2c_first_dynamic_bus_num = busnum + 1;            for (status = 0; len; len--, info++) {                struct i2c_devinfo    *devinfo;                devinfo = kzalloc(sizeof(*devinfo), GFP_KERNEL);                if (!devinfo) {                    pr_debug("i2c-core: can't register boardinfo!\n");                    status = -ENOMEM;                    break;                }                devinfo->busnum = busnum;                devinfo->board_info = *info;                list_add_tail(&devinfo->list, &__i2c_board_list); //跟踪__i2c_board_list            }            up_write(&__i2c_board_lock);            return status;        }        ......    2. cat drivers/i2c/i2c-boardinfo.c        ......        LIST_HEAD(__i2c_board_list);    一个公用的I2C链表头        EXPORT_SYMBOL_GPL(__i2c_board_list);        ......八、I2C adapter(适配器)跟踪:    1. cat drivers/i2c/busses/i2c-imx.c        ......        /* This will be the driver name the kernel reports */        #define DRIVER_NAME "imx-i2c"       //adapter和I2C控制器匹配的名字        /* Default value */        #define IMX_I2C_BIT_RATE    100000    /* 100kHz */        static struct platform_driver i2c_imx_driver = {            .remove        = __exit_p(i2c_imx_remove),            .driver    = {                .name    = DRIVER_NAME,                .owner    = THIS_MODULE,            }        };        static int __init i2c_adap_imx_init(void)        {            return platform_driver_probe(&i2c_imx_driver, i2c_imx_probe);  //跟踪函数,参数        }        subsys_initcall(i2c_adap_imx_init);        static void __exit i2c_adap_imx_exit(void)        {            platform_driver_unregister(&i2c_imx_driver);        }        module_exit(i2c_adap_imx_exit);        MODULE_LICENSE("GPL");        MODULE_AUTHOR("Darius Augulis");        MODULE_DESCRIPTION("I2C adapter driver for IMX I2C bus");  //这里说明了这个驱动的作用        MODULE_ALIAS("platform:" DRIVER_NAME);    2. cat drivers/base/platform.c        ......        int __init_or_module platform_driver_probe(struct platform_driver *drv,                int (*probe)(struct platform_device *))        {            int retval, code;            /* make sure driver won't have bind/unbind attributes */            drv->driver.suppress_bind_attrs = true;            /* temporary section violation during probe() */            /**             * 主要注意下面这行代码             */            drv->probe = probe;            retval = code = platform_driver_register(drv);            /*             * Fixup that section violation, being paranoid about code scanning             * the list of drivers in order to probe new devices.  Check to see             * if the probe was successful, and make sure any forced probes of             * new devices fail.             */            spin_lock(&drv->driver.bus->p->klist_drivers.k_lock);            drv->probe = NULL;            if (code == 0 && list_empty(&drv->driver.p->klist_devices.k_list))                retval = -ENODEV;            drv->driver.probe = platform_drv_probe_fail;            spin_unlock(&drv->driver.bus->p->klist_drivers.k_lock);            if (code != retval)                platform_driver_unregister(drv);            return retval;        }        EXPORT_SYMBOL_GPL(platform_driver_probe);        ......    3. cat drivers/i2c/busses/i2c-imx.c        ......        static int __init i2c_imx_probe(struct platform_device *pdev)        {            struct imx_i2c_struct *i2c_imx;            struct resource *res;            struct imxi2c_platform_data *pdata;            void __iomem *base;            resource_size_t res_size;            int irq;            int ret;            dev_dbg(&pdev->dev, "<%s>\n", __func__);            res = platform_get_resource(pdev, IORESOURCE_MEM, 0);            if (!res) {                dev_err(&pdev->dev, "can't get device resources\n");                return -ENOENT;            }            irq = platform_get_irq(pdev, 0);            if (irq < 0) {                dev_err(&pdev->dev, "can't get irq number\n");                return -ENOENT;            }            pdata = pdev->dev.platform_data;            if (pdata && pdata->init) {                ret = pdata->init(&pdev->dev);                if (ret)                    return ret;            }            res_size = resource_size(res);            if (!request_mem_region(res->start, res_size, DRIVER_NAME)) {                ret = -EBUSY;                goto fail0;            }            base = ioremap(res->start, res_size);            if (!base) {                dev_err(&pdev->dev, "ioremap failed\n");                ret = -EIO;                goto fail1;            }            i2c_imx = kzalloc(sizeof(struct imx_i2c_struct), GFP_KERNEL);            if (!i2c_imx) {                dev_err(&pdev->dev, "can't allocate interface\n");                ret = -ENOMEM;                goto fail2;            }            /* Setup i2c_imx driver structure */            strcpy(i2c_imx->adapter.name, pdev->name);            i2c_imx->adapter.owner        = THIS_MODULE;            i2c_imx->adapter.algo        = &i2c_imx_algo;            i2c_imx->adapter.dev.parent    = &pdev->dev;            i2c_imx->adapter.nr         = pdev->id;            i2c_imx->irq            = irq;            i2c_imx->base            = base;            i2c_imx->res            = res;            /* Get I2C clock */            i2c_imx->clk = clk_get(&pdev->dev, "i2c_clk");            if (IS_ERR(i2c_imx->clk)) {                ret = PTR_ERR(i2c_imx->clk);                dev_err(&pdev->dev, "can't get I2C clock\n");                goto fail3;            }            /* Request IRQ */            ret = request_irq(i2c_imx->irq, i2c_imx_isr, 0, pdev->name, i2c_imx);            if (ret) {                dev_err(&pdev->dev, "can't claim irq %d\n", i2c_imx->irq);                goto fail4;            }            /* Init queue */            init_waitqueue_head(&i2c_imx->queue);            /* Set up adapter data */            i2c_set_adapdata(&i2c_imx->adapter, i2c_imx);            /* Set up clock divider */            if (pdata && pdata->bitrate)                i2c_imx_set_clk(i2c_imx, pdata->bitrate);            else                i2c_imx_set_clk(i2c_imx, IMX_I2C_BIT_RATE);            /* Set up chip registers to defaults */            writeb(0, i2c_imx->base + IMX_I2C_I2CR);            writeb(0, i2c_imx->base + IMX_I2C_I2SR);            /* Add I2C adapter */            ret = i2c_add_numbered_adapter(&i2c_imx->adapter);            if (ret < 0) {                dev_err(&pdev->dev, "registration failed\n");                goto fail5;            }            /* Set up platform driver data */            platform_set_drvdata(pdev, i2c_imx);            dev_dbg(&i2c_imx->adapter.dev, "claimed irq %d\n", i2c_imx->irq);            dev_dbg(&i2c_imx->adapter.dev, "device resources from 0x%x to 0x%x\n",                i2c_imx->res->start, i2c_imx->res->end);            dev_dbg(&i2c_imx->adapter.dev, "allocated %d bytes at 0x%x \n",                res_size, i2c_imx->res->start);            dev_dbg(&i2c_imx->adapter.dev, "adapter name: \"%s\"\n",                i2c_imx->adapter.name);            dev_dbg(&i2c_imx->adapter.dev, "IMX I2C adapter registered\n");            return 0;   /* Return OK */        fail5:            free_irq(i2c_imx->irq, i2c_imx);        fail4:            clk_put(i2c_imx->clk);        fail3:            kfree(i2c_imx);        fail2:            iounmap(base);        fail1:            release_mem_region(res->start, resource_size(res));        fail0:            if (pdata && pdata->exit)                pdata->exit(&pdev->dev);            return ret; /* Return error number */        }        ......九、I2C设备追踪:    1. cat drivers/misc/eeprom/max6875.c        ......        static const struct i2c_device_id max6875_id[] = {            { "max6875", 0 },            { }        };        static struct i2c_driver max6875_driver = {            .driver = {                .name    = "max6875",            },            .probe        = max6875_probe,    //跟踪函数            .remove        = max6875_remove,            .id_table    = max6875_id,        };        static int __init max6875_init(void)        {            return i2c_add_driver(&max6875_driver); //跟踪函数        }        static void __exit max6875_exit(void)        {            i2c_del_driver(&max6875_driver);        }        MODULE_AUTHOR("Ben Gardner 
      
       ");        MODULE_DESCRIPTION("MAX6875 driver");        MODULE_LICENSE("GPL");        module_init(max6875_init);        module_exit(max6875_exit);                   2. cat include/linux/i2c.h        ......        static inline int i2c_add_driver(struct i2c_driver *driver)        {            return i2c_register_driver(THIS_MODULE, driver);    //跟踪函数        }        ......    3. cat drivers/i2c/i2c-core.c        ......        int i2c_register_driver(struct module *owner, struct i2c_driver *driver)        {            ......            driver->driver.owner = owner;            driver->driver.bus = &i2c_bus_type;     //跟踪数据结构            /* When registration returns, the driver core             * will have called probe() for all matching-but-unbound devices.             */            res = driver_register(&driver->driver); //这里就跟踪到这里结束了            ......              /* Walk the adapters that are already present */            i2c_for_each_dev(driver, __process_new_driver);   //跟踪这个函数            return 0;        }        EXPORT_SYMBOL(i2c_register_driver);        ......    4. cat drivers/i2c/i2c-core.c        ......         struct bus_type i2c_bus_type = {            .name        = "i2c",            .match        = i2c_device_match,            .probe        = i2c_device_probe,            .remove        = i2c_device_remove,            .shutdown    = i2c_device_shutdown,            .pm        = &i2c_device_pm_ops,        };        EXPORT_SYMBOL_GPL(i2c_bus_type);        ......        十、跟踪__process_new_driver参数:    1. cat drivers/i2c/i2c-core.c        ......        static int __process_new_driver(struct device *dev, void *data)        {            if (dev->type != &i2c_adapter_type)                return 0;            //跟踪to_i2c_adapter参数,部队i2c_do_add_adapter()函数进行跟踪,到这里结束            return i2c_do_add_adapter(data, to_i2c_adapter(dev));         }        ......   2. cat include/linux/i2c.h        ......        #define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)        ......十一、跟踪i2c_for_each_dev()函数:    1. cat drivers/i2c/i2c-core.c        ......        int i2c_for_each_dev(void *data, int (*fn)(struct device *, void *))        {            int res;            mutex_lock(&core_lock);            res = bus_for_each_dev(&i2c_bus_type, NULL, data, fn);  //跟踪函数            mutex_unlock(&core_lock);            return res;        }        EXPORT_SYMBOL_GPL(i2c_for_each_dev);        ......   2. cat drivers/base/bus.c        ......        /**         * 这一部分只跟踪到这里,因为从函数名,你可以知道没必要再跟下去了         */        int bus_for_each_dev(struct bus_type *bus, struct device *start,                     void *data, int (*fn)(struct device *, void *))        {            /**             *             *  struct bus_type {             *      ......             *             *      struct subsys_private *p;             *  };             *             *  struct subsys_private {             *      ......             *      struct klist klist_devices;             *      struct klist klist_drivers;             *      ......             *  };             *             *  struct device {             *      ......             *      struct device_private    *p;             *      ......             *  };             *             *  struct device_private {             *      ......             *      struct klist_node knode_bus;             *      void *driver_data;             *      struct device *device;             *  };             */            struct klist_iter i;            struct device *dev;            ......            klist_iter_init_node(&bus->p->klist_devices, &i,                         (start ? &start->p->knode_bus : NULL));            while ((dev = next_device(&i)) && !error)                    error = fn(dev, data);            klist_iter_exit(&i);            return error;        }        EXPORT_SYMBOL_GPL(bus_for_each_dev);        ......十二、跟踪max6875_probe()函数:    cat drivers/misc/eeprom/max6875.c        ......        static int max6875_probe(struct i2c_client *client,                     const struct i2c_device_id *id)        {            struct i2c_adapter *adapter = client->adapter;            struct max6875_data *data;            int err;            if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_WRITE_BYTE_DATA                             | I2C_FUNC_SMBUS_READ_BYTE))                return -ENODEV;            /* Only bind to even addresses */            if (client->addr & 1)                return -ENODEV;            if (!(data = kzalloc(sizeof(struct max6875_data), GFP_KERNEL)))                return -ENOMEM;            /* A fake client is created on the odd address */            data->fake_client = i2c_new_dummy(client->adapter, client->addr + 1);            if (!data->fake_client) {                err = -ENOMEM;                goto exit_kfree;            }            /* Init real i2c_client */            i2c_set_clientdata(client, data);            mutex_init(&data->update_lock);            err = sysfs_create_bin_file(&client->dev.kobj, &user_eeprom_attr);            if (err)                goto exit_remove_fake;            return 0;        exit_remove_fake:            i2c_unregister_device(data->fake_client);        exit_kfree:            kfree(data);            return err;        }