dm6467中I2C总线驱动分析

I2C adapter driver层    I2C adapter driver层即I2C适配器驱动层，每种处理器平台都有自己的适配器驱动，属于平台移植相关层。它的职责是为系统中每条I2C总线实现相应的读写方法。但是适配器驱动本身并不会进行任何的通讯，而是等待设备驱动调用其函数。    在系统开机时，I2C适配器驱动被首先装载。一个适配器驱动用于支持一条特定的I2C总线的读写。一个适配器驱动通常需要两个模块，一个struct i2c_adapter和一个struct i2c_algorithm来描述。 

i2c adapter 构造一个对I2C core层接口的数据结构，并通过相应的接口函数向I2C core注册一个适配器。i2c_algorithm主要实现对I2C总线访问的算法，master_xfer和smbus_xfer即I2C adapter底层对I2C总线读写方法的实现，相关的数据结构如下：

	 /** The following structs are for those who like to implement new bus drivers:* i2c_algorithm is the interface to a class of hardware solutions which can* be addressed using the same bus algorithms - i.e. bit-banging or the PCF8584* to name two of the most common.*/struct i2c_algorithm {/* If an adapter algorithm can't do I2C-level access, set master_xferto NULL. If an adapter algorithm can do SMBus access, setsmbus_xfer. If set to NULL, the SMBus protocol is simulatedusing common I2C messages *//* master_xfer should return the number of messages successfullyprocessed, or a negative value on error */int (*master_xfer)(struct i2c_adapter *adap, struct i2c_msg *msgs,int num);int (*smbus_xfer) (struct i2c_adapter *adap, u16 addr,unsigned short flags, char read_write,u8 command, int size, union i2c_smbus_data *data);/* To determine what the adapter supports */u32 (*functionality) (struct i2c_adapter *);};

主要就是master_xfer方法，其和具体的总线控制器相关，不同的CPU在实现上会有差异。

	/** i2c_adapter is the structure used to identify a physical i2c bus along* with the access algorithms necessary to access it.*/struct i2c_adapter {struct module *owner;unsigned int id;unsigned int class;		  /* classes to allow probing for */const struct i2c_algorithm *algo; /* the algorithm to access the bus */void *algo_data;/* data fields that are valid for all devices	*/struct rt_mutex bus_lock;int timeout;			/* in jiffies */int retries;struct device dev;		/* the adapter device */int nr;char name[48];struct completion dev_released;struct list_head userspace_clients;};

 Algo是和底层硬件的接口，标识了具体的物理总线传输的实现。
    Userspace_clients为使用该总线的client链表。
    Nr为该适配器也就是某条I2C总线占据的全局编号。
    bus_lock总线的互斥锁，防止总线冲突。
    Linux中，I2C adapter driver层的代码位于drivers/i2c/busses目录。

 I2C device driver层

    I2C device driver层为用户接口层，其为用户提供了通过I2C总线访问具体设备的接口。
    I2C的device driver层可以用两个模块来描述，struct i2c_driver和struct i2c_client。
    i2c_client和i2c_driver分别构造对I2C core层接口的数据结构，并且通过相关的接口函数向 I2C Core注册I2C设备驱动。相关的数据结构如下：

	/*** struct i2c_driver - represent an I2C device driver* @class: What kind of i2c device we instantiate (for detect)* @attach_adapter: Callback for bus addition (for legacy drivers)* @detach_adapter: Callback for bus removal (for legacy drivers)* @probe: Callback for device binding* @remove: Callback for device unbinding* @shutdown: Callback for device shutdown* @suspend: Callback for device suspend* @resume: Callback for device resume* @command: Callback for bus-wide signaling (optional)* @driver: Device driver model driver* @id_table: List of I2C devices supported by this driver* @detect: Callback for device detection* @address_list: The I2C addresses to probe (for detect)* @clients: List of detected clients we created (for i2c-core use only)** The driver.owner field should be set to the module owner of this driver.* The driver.name field should be set to the name of this driver.** For automatic device detection, both @detect and @address_data must* be defined. @class should also be set, otherwise only devices forced* with module parameters will be created. The detect function must* fill at least the name field of the i2c_board_info structure it is* handed upon successful detection, and possibly also the flags field.** If @detect is missing, the driver will still work fine for enumerated* devices. Detected devices simply won't be supported. This is expected* for the many I2C/SMBus devices which can't be detected reliably, and* the ones which can always be enumerated in practice.** The i2c_client structure which is handed to the @detect callback is* not a real i2c_client. It is initialized just enough so that you can* call i2c_smbus_read_byte_data and friends on it. Don't do anything* else with it. In particular, calling dev_dbg and friends on it is* not allowed.*/struct i2c_driver {unsigned int class;/* Notifies the driver that a new bus has appeared or is about to be* removed. You should avoid using this if you can, it will probably* be removed in a near future.*/int (*attach_adapter)(struct i2c_adapter *);int (*detach_adapter)(struct i2c_adapter *);/* Standard driver model interfaces */int (*probe)(struct i2c_client *, const struct i2c_device_id *);int (*remove)(struct i2c_client *);/* driver model interfaces that don't relate to enumeration  */void (*shutdown)(struct i2c_client *);int (*suspend)(struct i2c_client *, pm_message_t mesg);int (*resume)(struct i2c_client *);/* Alert callback, for example for the SMBus alert protocol.* The format and meaning of the data value depends on the protocol.* For the SMBus alert protocol, there is a single bit of data passed* as the alert response's low bit ("event flag").*/void (*alert)(struct i2c_client *, unsigned int data);/* a ioctl like command that can be used to perform specific functions* with the device.*/int (*command)(struct i2c_client *client, unsigned int cmd, void *arg);struct device_driver driver;const struct i2c_device_id *id_table;/* Device detection callback for automatic device creation */int (*detect)(struct i2c_client *, struct i2c_board_info *);const unsigned short *address_list;struct list_head clients;};

Driver是为device服务的，i2c_driver注册时会扫描i2c bus上的设备，进行驱动和设备的绑定。主要有两种接口attach_adapter和probe，二者分别针对旧的和新式的驱动。 

通常来说i2c_client对应着I2C总线上某个特定的slave或者是user space的某个用户对应，而此时的slave可以动态变化。
    Linux中，I2C device driver层的代码位于drivers/i2c/chips目录。

dm6467 I2C adapter驱动
    在Linux内核中，I2C adapter驱动位于drivers/i2c/busses目录下，DM6467 的I2C adapter驱动程序为drivers/i2c/busses/i2c-davinci.c

 I2C adapter驱动，本质上就是实现了具体的总线传输算法并向核心层注册适配器。该驱动的注册采用Platform驱动和设备机制。

I2C adapter的Platform device
   DM6467中Platform device的注册的代码位于内核的arch/arm/mach-davinci/devices.c

	在arch/arm/mach-davinci/devices.c中。Platmform device 定义如下：32 static struct resource i2c_resources[] = {33         {34                 .start          = DAVINCI_I2C_BASE,35                 .end            = DAVINCI_I2C_BASE + 0x40,36                 .flags          = IORESOURCE_MEM,37         },38         {39                 .start          = IRQ_I2C,40                 .flags          = IORESOURCE_IRQ,41         },42 };43 44 static struct davinci_i2c_platform_data dm644x_i2c_data = {45         .bus_freq       = 20,46         .bus_delay      = 100,47 };48 49 static struct davinci_i2c_platform_data dm355_i2c_data = {50         .bus_freq       = 20,51         .bus_delay      = 100,52 };53 54 static struct davinci_i2c_platform_data dm646x_i2c_data = {55         .bus_freq       = 100,56         .bus_delay      = 0,57 };58 59 static struct platform_device i2c_device = {60         .name           = "i2c_davinci",61         .id             = 1,62         .dev            = {63                 .platform_data = &dm355_i2c_data,64         },65         .num_resources  = ARRAY_SIZE(i2c_resources),66         .resource       = i2c_resources,67 };i2c_resources[] 定义了I2C的地址范围、中断号等相关信息，platform_device i2c_device 初始化的时候初始化了dm355的数据，在davinci_init_cpu_i2c中再给i2c_device.dev.platform_data赋值为dm6467的数据。132 static struct platform_device *devices[] __initdata = {133         &i2c_device,134         &watchdog_device,135         &usb_device,136 };138 static void __init davinci_init_cpu_i2c(void)139 {140         if (cpu_is_davinci_dm644x())141                 i2c_device.dev.platform_data = &dm644x_i2c_data;142         else if (cpu_is_davinci_dm6467())143                 i2c_device.dev.platform_data = &dm646x_i2c_data;144 145         /* all others default to use dm355 because dm355 uses the max speed */146 }147 最后在davinci_init_devices中调用drivers/base/platform.c 提供的导出函数platform_add_devices添加设备。160 static int __init davinci_init_devices(void)161 {162         davinci_init_cpu_i2c();163         davinci_init_cpu_usb();164         platform_add_devices(devices, ARRAY_SIZE(devices));165         return 0;166 }167 arch_initcall(davinci_init_devices);platform_add_devices函数具体如下：110 int platform_add_devices(struct platform_device **devs, int num)111 {112         int i, ret = 0;113                 114         for (i = 0; i < num; i++) {115                 ret = platform_device_register(devs[i]);116                 if (ret) {117                         while (--i >= 0)118                                 platform_device_unregister(devs[i]);119                         break;120                 }121         }122         123         return ret;124 }125 EXPORT_SYMBOL_GPL(platform_add_devices);

     注册完成后，中断号及寄存器的基地址等信息会在设备树中描述了，此后只需利用 platform_get_resource等标准接口自动获取即可，实现了驱动和资源的分离。

 platform_get_resource如下：30 /**     31  *      platform_get_resource - get a resource for a device32  *      @dev: platform device33  *      @type: resource type34  *      @num: resource index35  */                     36 struct resource *               37 platform_get_resource(struct platform_device *dev, unsigned int type,38                       unsigned int num)39 {       40         int i;41         42         for (i = 0; i < dev->num_resources; i++) {43                 struct resource *r = &dev->resource[i];44 45                 if ((r->flags & (IORESOURCE_IO|IORESOURCE_MEM|46                                  IORESOURCE_IRQ|IORESOURCE_DMA))47                     == type)48                         if (num-- == 0)49                                 return r;50         }51         return NULL;52 }

I2C adapter的Platform driver
dm6467中Platform driver的注册的代码位于内核的ddrivers/i2c/busses/i2c-davinci.c中，该驱动的注册目的是初始化dm6467的I2C adapter，提供I2C总线传输的具体实现，并且向I2C core注册I2C adapter。

Platform driver的定义 

 在drivers/i2c/busses/i2c-davinci.c中Platform driver的定义 如下：

	599 static struct platform_driver davinci_i2c_driver = {600         .probe          = davinci_i2c_probe,601         .remove         = davinci_i2c_remove,602         .driver         = {603                 .name   = "i2c_davinci",604                 .owner  = THIS_MODULE,605         },606 };其注册方法如下：608 /* I2C may be needed to bring up other drivers */609 static int __init davinci_i2c_init_driver(void)610 {611         return platform_driver_register(&davinci_i2c_driver);612 }613 subsys_initcall(davinci_i2c_init_driver);

通过platform_driver_register()函数注册Platform driver davinci_i2c_driver时，会扫描platform bus上的所有设备，由于匹配因子是name即"i2c_davinci"，而之前已经将name为"i2c_davinci"的Platform device注册到platform bus上，因此匹配成功，调用函数davinci_i2c_probe将设备和驱动绑定起来。 

davinci_i2c_probe的过程如下：

通过platform_get_resource获*mem, *irq, 资源，分配内存，初始化struct davinci_i2c_dev，申请i2c_davinci_isr中断，初始化 struct i2c_adapter，并通过i2c-core提供的i2c_add_adapter注册i2c_adapter。具体如下：

	487 static int davinci_i2c_probe(struct platform_device *pdev)488 {489         struct davinci_i2c_dev *dev;490         struct i2c_adapter *adap;491         struct resource *mem, *irq, *ioarea;492         int r;493 494         /* NOTE: driver uses the static register mapping */495         mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);496         if (!mem) {497                 dev_err(&pdev->dev, "no mem resource?\n");498                 return -ENODEV;499         }500 501         irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);502         if (!irq) {503                 dev_err(&pdev->dev, "no irq resource?\n");504                 return -ENODEV;505         }506 507         ioarea = request_mem_region(mem->start, (mem->end - mem->start) + 1,508                                     pdev->name);509         if (!ioarea) {510                 dev_err(&pdev->dev, "I2C region already claimed\n");511                 return -EBUSY;512         }513 514         dev = kzalloc(sizeof(struct davinci_i2c_dev), GFP_KERNEL);515         if (!dev) {516                 r = -ENOMEM;517                 goto err_release_region;518         }519 520         dev->dev = get_device(&pdev->dev);521         dev->irq = irq->start;522         platform_set_drvdata(pdev, dev);523 524         dev->clk = clk_get(&pdev->dev, "I2CCLK");525         if (IS_ERR(dev->clk)) {526                 r = -ENODEV;527                 goto err_free_mem;528         }529         clk_enable(dev->clk);530 531         dev->base = (void __iomem *)IO_ADDRESS(mem->start);532         i2c_davinci_init(dev);533 534         r = request_irq(dev->irq, i2c_davinci_isr, 0, pdev->name, dev);535         if (r) {536                 dev_err(&pdev->dev, "failure requesting irq %i\n", dev->irq);537                 goto err_unuse_clocks;538         }539 540         adap = &dev->adapter;541         i2c_set_adapdata(adap, dev);542         adap->owner = THIS_MODULE;543         adap->class = I2C_CLASS_HWMON;544         strlcpy(adap->name, "DaVinci I2C adapter", sizeof(adap->name));545         adap->algo = &i2c_davinci_algo;546         adap->dev.parent = &pdev->dev;547 548         /* FIXME */549         adap->timeout = 1;550         adap->retries = 1;551 552         adap->nr = pdev->id;553         r = i2c_add_adapter(adap);554         if (r) {555                 dev_err(&pdev->dev, "failure adding adapter\n");556                 goto err_free_irq;557         }558 559         return 0;560 561 err_free_irq:562         free_irq(dev->irq, dev);563 err_unuse_clocks:564         clk_disable(dev->clk);565         clk_put(dev->clk);566         dev->clk = NULL;567 err_free_mem:568         platform_set_drvdata(pdev, NULL);569         put_device(&pdev->dev);570         kfree(dev);571 err_release_region:572         release_mem_region(mem->start, (mem->end - mem->start) + 1);573 574         return r;575 }

原文主要参考了：http://blog.csdn.net/kellycan/article/details/6394737