Linux下DM644x设备驱动I2C之总线驱动（一）详解

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linux DM6441下I2C设备驱动的开发

前言：

和常用的Linux I2C的驱动开发一样，主要包括总线Bus驱动，以及相应的设备驱动开发。

总线驱动和CPU的关系较为密切，涉及到相关硬件的操作。

本文以Linux2.6.1和Dm6441简单解析一下整个驱动的编写架构。

 

1.   总线驱动

涉及到总线驱动的相关代码在drivers/i2c/bussses下面，该目录下是各CPU的I2C模块涉及到的内容，这里我们选择i2c-davinci.c文件

总线驱动中Init函数i2c_davinci_init如下：

static int __init i2c_davinci_init(void){int status;struct device *dev = NULL;DEB0("%s %s", __TIME__, __DATE__);DEB1("i2c_davinci_init()");#if 0if (i2c_davinci_busFreq > 200)i2c_davinci_busFreq = 400;/*Fast mode */elsei2c_davinci_busFreq = 100;/*Standard mode */#endifi2c_clock = clk_get (dev, "I2CCLK"); //获取I2C输入时钟批频率27MHzif (IS_ERR(i2c_clock))        return -1;clk_use (i2c_clock);clk_enable (i2c_clock);i2c_davinci_inputClock = clk_get_rate (i2c_clock);    //获取I2C输入时钟批频率27MHzDEB1 ("IP CLOCK = %ld", i2c_davinci_inputClock);memset(&i2c_davinci_dev, 0, sizeof(i2c_davinci_dev));init_waitqueue_head(&i2c_davinci_dev.cmd_wait);i2c_davinci_dev.regs = (davinci_i2cregsovly)I2C_BASE;      //I2C控制器相关寄存器所在地址status = (int)request_region(I2C_BASE, I2C_IOSIZE, MODULE_NAME); //申请一块IO输入输出区域#define MODULE_NAME "DaVinci I2C"if (!status) {i2c_err("I2C is already in use\n");return -ENODEV;}status = request_irq(IRQ_I2C, i2c_davinci_isr, 0, "i2c",     &i2c_davinci_dev);  //申请I2C中断号IRQ_I2C=39if (status) {i2c_err("failed to request I2C IRQ");goto do_release_region;}i2c_set_adapdata(&i2c_davinci_adap, &i2c_davinci_dev);  //adap设备的驱动程序私有数据i2c_davinci_adap->dev->driver_data =i2c_davinci_devstatus = i2c_add_adapter(&i2c_davinci_adap);    //I2C上添加adapterif (status) {i2c_err("failed to add adapter");goto do_free_irq;}i2c_davinci_reset(&i2c_davinci_dev);   //完成I2C相关寄存器的初始化if (driver_register(&davinci_i2c_driver) != 0)            // I2C驱动注册printk(KERN_ERR "Driver register failed for davinci_i2c\n");if (platform_device_register(&davinci_i2c_device) != 0) {printk(KERN_ERR "Device register failed for i2c\n");driver_unregister(&davinci_i2c_driver);}return 0;      do_free_irq:free_irq(IRQ_I2C, &i2c_davinci_dev);      do_release_region:release_region(I2C_BASE, I2C_IOSIZE);return status;}

操作主要围绕以下4个结构体展开：

static struct i2c_algorithm i2c_davinci_algo = {            //主要涉及相关的I2C通信协议以及数据的传输和接受.name = "DAVINCI I2C algorithm",.id = I2C_ALGO_EXP,.master_xfer = i2c_davinci_xfer,.smbus_xfer = NULL,.slave_send = NULL,.slave_recv = NULL,.algo_control = NULL,.functionality = i2c_davinci_func,};static struct i2c_adapter i2c_davinci_adap = {       //对I2C通信协议的封装，定义的适配器实例.owner = THIS_MODULE,.name = "DAVINCI I2C adapter",.id = I2C_ALGO_EXP,.algo = &i2c_davinci_algo,.algo_data = NULL,.client_register = NULL,.client_unregister = NULL,};static struct device_driver davinci_i2c_driver = {            //达芬奇的设备驱动.name = "davinci_i2c",.bus = &platform_bus_type,.remove = davinci_i2c_remove,};static struct platform_device davinci_i2c_device = {         //定义的达芬奇平台设备.name = "i2c",.id = -1,.dev = {.driver = &davinci_i2c_driver,.release = davinci_i2c_device_release,},};

结合以上两段代码，可以知道以下内容

1 .在模块初始化函数中完成适配器与设备。的连接了设备驱动davinci_i2c_driver和平台设备davinci_i2c_device的注册

2.获取I2C相关端口的申请，I2C相应寄存器的物理首地址0x01C21000，完成了I2C模块初始化操作以及IRQ_I2C=39的中断申请。

在这里对I2C模块的初始化进行解析，内容如下：

static int i2c_davinci_reset(struct i2c_davinci_device *dev){u16 psc;u32 clk;        DEB1("i2c: reset called");/* put I2C into reset */dev->regs->icmdr &= ~DAVINCI_I2C_ICMDR_IRS_MASK; //首先需复位I2C模块        /* NOTE: I2C Clock divider programming info  * As per I2C specs the following formulas provide prescalar         * and low/high divider values  *  * input clk --> PSC Div -----------> ICCL/H Div --> output clock  *                       module clk  *  * output clk = module clk / (PSC + 1) [ (ICCL + d) + (ICCH + d) ]  *  * Thus,  * (ICCL + ICCH) = clk = (input clk / ((psc +1) * output clk)) - 2d;  *  * where if PSC == 0, d = 7,  *       if PSC == 1, d = 6  *       if PSC > 1 , d = 5  */psc = 26; /* To get 1MHz clock */  clk = ((i2c_davinci_inputClock/(psc + 1)) / (i2c_davinci_busFreq * 1000)) - 10; //i2c_davinci_busFreq=20dev->regs->icpsc = psc;  //PSC寄存器写26，即预分频数27dev->regs->icclkh = (50 * clk) / 100; /* duty cycle should be 50% */dev->regs->icclkl = (clk - dev->regs->icclkh); //高低电平配置内容DEB1("CLK  = %d", clk);DEB1("PSC  = %d", dev->regs->icpsc);DEB1("CLKL = %d", dev->regs->icclkl);DEB1("CLKH = %d", dev->regs->icclkh);/* Set Own Address: */dev->regs->icoar = i2c_davinci_own_addr; //oxa/* Enable interrupts */dev->regs->icimr = I2C_DAVINCI_INTR_ALL;   //所有中断都使能/* Take the I2C module out of reset: */dev->regs->icmdr |= DAVINCI_I2C_ICMDR_IRS_MASK;    //使能I2C模块return 0;}

主要完成Dm6441上I2C的总线时钟的配置。以及做一些中断使能的初始化。在这里都是对dev->regs这个结构体指针的内容

该结构体的实际内容如下：

typedef struct {u16 icoar;u8 rsvd0[2];u16 icimr;u8 rsvd1[2];u16 icstr;u8 rsvd2[2];u16 icclkl;u8 rsvd3[2];u16 icclkh;u8 rsvd4[2];u16 iccnt;u8 rsvd5[2];u16 icdrr;u8 rsvd6[2];u16 icsar;u8 rsvd7[2];u16 icdxr;u8 rsvd8[2];u16 icmdr;u8 rsvd9[2];u16 icivr;u8 rsvd10[2];u16 icemdr;u8 rsvd11[2];u16 icpsc;u8 rsvd12[2];u16 icpid1;u8 rsvd13[2];u16 icpid2;u8 rsvd14[14];u32 ipcfunc;u32 icpdir;u32 icpdin;u32 icpdout;u32 icpdset;u32 icpdclr;} davinci_i2cregs;/**************************************************************************\* Overlay structure typedef definition\**************************************************************************/typedef volatile davinci_i2cregs *davinci_i2cregsovly;

涉及的内容是DM6441 I2C模块的相关寄存器。在获取寄存器的物理首地址之后，就可以直接对这个结构体实例的内容写数值，该结构体被包含在以下结构体中

struct i2c_davinci_device {int cmd_complete, cmd_err;wait_queue_head_t cmd_wait;u8 *buf;size_t buf_len;davinci_i2cregsovly regs;};

 

这里的另一块内容是添加适配器到I2C驱动中使用i2c_add_adapter函数完成i2c_davinci_adap（该结构体实例内容见上述代码）

int i2c_add_adapter(struct i2c_adapter *adap){int id, res = 0;struct list_head   *item;struct i2c_driver  *driver;down(&core_lists);if (idr_pre_get(&i2c_adapter_idr, GFP_KERNEL) == 0) {res = -ENOMEM;goto out_unlock;}res = idr_get_new(&i2c_adapter_idr, NULL, &id);if (res < 0) {if (res == -EAGAIN)res = -ENOMEM;goto out_unlock;}adap->nr =  id & MAX_ID_MASK;init_MUTEX(&adap->bus_lock);init_MUTEX(&adap->clist_lock);list_add_tail(&adap->list,&adapters);INIT_LIST_HEAD(&adap->clients);/* Add the adapter to the driver core. * If the parent pointer is not set up, * we add this adapter to the host bus. */if (adap->dev.parent == NULL)adap->dev.parent = &platform_bus;sprintf(adap->dev.bus_id, "i2c-%d", adap->nr);adap->dev.driver = &i2c_adapter_driver;   //适配器的设备驱动指向i2c_adapter_driveradap->dev.release = &i2c_adapter_dev_release;device_register(&adap->dev);                       //适配器设备注册device_create_file(&adap->dev, &dev_attr_name);/* Add this adapter to the i2c_adapter class */memset(&adap->class_dev, 0x00, sizeof(struct class_device));adap->class_dev.dev = &adap->dev;adap->class_dev.class = &i2c_adapter_class;strlcpy(adap->class_dev.class_id, adap->dev.bus_id, BUS_ID_SIZE);class_device_register(&adap->class_dev);/* inform drivers of new adapters */list_for_each(item,&drivers) {driver = list_entry(item, struct i2c_driver, list);if (driver->flags & I2C_DF_NOTIFY)/* We ignore the return code; if it fails, too bad */driver->attach_adapter(adap);}dev_dbg(&adap->dev, "registered as adapter #%d\n", adap->nr);out_unlock:up(&core_lists);return res;}

在该函数内主要完成适配器结构体中成员变量设备dev的初始化，紧接着完成适配器这个抽象设备的注册，再完成适配器设备类的注册以及相关设备节点的生成。