Linux下DM644x设备驱动I2C之总线驱动
Linux DM6441下I2C设备驱动的开发
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 0
- if (i2c_davinci_busFreq > 200)
- i2c_davinci_busFreq = 400; /*Fast mode */
- else
- i2c_davinci_busFreq = 100; /*Standard mode */
- #endif
- i2c_clock = clk_get (dev, "I2CCLK"); //获取I2C输入时钟批频率27MHz
- if (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27MHz
- DEB1 ("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=39
- if (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_dev
- status = i2c_add_adapter(&i2c_davinci_adap); //I2C上添加adapter
- if (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=20
- dev->regs->icpsc = psc; //PSC寄存器写26，即预分频数27
- dev->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_driver
- adap->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。
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