本驱动基于linux2.6.32.2
i2c遵循的也是总线设备驱动框架,具体流程如下:
当加入驱动(driver)时:
i2c_add_driver //进行驱动注册
i2c_register_driver(THIS_MODULE, driver);
driver_register(&driver->driver); //把驱动加入总线驱动链表
bus_for_each_dev(&i2c_bus_type, NULL, driver, __attach_adapter); //对于总线上设备链表的每一个设备进行遍历
__attach_adapter //对每一次遍历调用__attach_adapter函数
to_i2c_adapter(dev); //寻找出该设备对应的适配器
i2c_detect(adapter, driver); //对每个适配器进行通信检测,检查是否存在该适配器
driver->attach_adapter(adapter); //调用驱动的attach_adapter函数(该函数需要自己设定,当然,做什么也是自己决定)
当加入适配器(adapter)时:
i2c_add_adapter //进行适配器注册
i2c_register_adapter
device_register(&adap->dev); //对适配器内的device进行注册
device_add(dev); //device加入链表
bus_for_each_drv(&i2c_bus_type, NULL, adap,i2c_do_add_adapter); //对于总线上驱动链表的每一个驱动进行遍历
i2c_do_add_adapter //对于每一次遍历调用该函数
i2c_detect(adapter, driver); //对每个适配器进行通信检测,检查是否存在该适配器
driver->attach_adapter(adapter); //调用驱动的attach_adapter函数(该函数需要自己设定,当然,做什么也是自己决定)
总线设备驱动框架遵从硬件设备跟驱动分离的原则
对于i2c设备,
device就是对应于i2c硬件设备,在device上加了一层封装,也就是adapter,其中adapter提供传输函数
driver就是i2c设备的驱动操作层,当device跟driver连接上之后,我们就可以在driver的内部函数attach_adapter函数内做进一步操作.
i2c_client：
i2c_client能用于连接adapter跟driver，起到中间节点的作用。
attach_adapter会提供本driver匹配的adapter结构体指针,我们可以通过构造一个i2c_client来接收该指针
本驱动提供的是字符设备操作,因此需要在attach_adapter内进行fops注册
由于在read/write等需要操作i2c硬件,因此用到函数i2c_transfer函数,该函数最终会调用到adap->algo->master_xfer(adap, msgs, num),
也就是adapter内定义的函数.该函数需要的参数有:相应的adapter,msg(其内部包含该次通信的源,目的,长度),和mun(msg的数目).
i2c_client结构体也用于存储这些传输所需参数。
驱动代码:
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#include <linux/kernel.h> #include <linux/init.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/jiffies.h> #include <linux/i2c.h> #include <linux/mutex.h> #include <linux/fs.h> #include <asm/uaccess.h> static struct i2c_client * at24cxx_client; static int major; static struct class *cls; static struct class_device *clsdev; static struct i2c_driver at24cxx_driver; static unsigned short ignore[] = { I2C_CLIENT_END }; static unsigned short normal_addr[] = { 0x50, I2C_CLIENT_END }; /* 地址值是7位 */ /* 改为0x60的话, 由于不存在设备地址为0x60的设备, 所以at24cxx_detect不被调用 */ static unsigned short force_addr[] = {ANY_I2C_BUS, 0x60, I2C_CLIENT_END}; static unsigned short * forces[] = {force_addr, NULL}; static struct i2c_client_address_data addr_data = { .normal_i2c = normal_addr, /* 要发出S信号和设备地址并得到ACK信号,才能确定存在这个设备 */ .probe = ignore, .ignore = ignore, //.forces = forces, /* 强制认为存在这个设备 */ }; static ssize_t at24cxx_read(struct file *file, char __user *buf, size_t size, loff_t * offset) { unsigned char address; unsigned char data; struct i2c_msg msg[2]; int ret; /* address = buf[0] * data = buf[1] */ if (size != 1) return -EINVAL; copy_from_user(&address, buf, 1); /* 数据传输三要素: 源,目的,长度 */ /* 读AT24CXX时,要先把要读的存储空间的地址发给它 */ msg[0].addr = at24cxx_client->addr; /* 目的 */ msg[0].buf = &address; /* 源 */ msg[0].len = 1; /* 地址=1 byte */ msg[0].flags = 0; /* 表示写 */ /* 然后启动读操作 */ msg[1].addr = at24cxx_client->addr; /* 源 */ msg[1].buf = &data; /* 目的 */ msg[1].len = 1; /* 数据=1 byte */ msg[1].flags = I2C_M_RD; /* 表示读 */ printk("adapter name:%s\n",at24cxx_client->adapter->name); if(at24cxx_client->adapter==NULL) printk("adapter not init\n"); ret = i2c_transfer(at24cxx_client->adapter, msg, 2); printk("transfer_ret:%d\n",ret); if (ret == 2) { copy_to_user(buf, &data, 1); return 1; } else return -EIO; } static ssize_t at24cxx_write(struct file *file, const char __user *buf, size_t size, loff_t *offset) { unsigned char val[2]; struct i2c_msg msg[1]; int ret; /* address = buf[0] * data = buf[1] */ if (size != 2) return -EINVAL; copy_from_user(val, buf, 2); /* 数据传输三要素: 源,目的,长度 */ msg[0].addr = at24cxx_client->addr; /* 目的 */ msg[0].buf = val; /* 源 */ msg[0].len = 2; /* 地址+数据=2 byte */ msg[0].flags = 0; /* 表示写 */ if(at24cxx_client->adapter==NULL) printk("adapter not init\n"); printk("adapter name:%s\n",at24cxx_client->adapter->name); ret = i2c_transfer(at24cxx_client->adapter, msg, 1); printk("transfer_ret:%d\n",ret); if (ret == 1) return 2; else return -EIO; } static struct file_operations at24cxx_fops = { .owner = THIS_MODULE, .read = at24cxx_read, .write = at24cxx_write, }; static int at24cxx_detect(struct i2c_adapter *adapter, int address, int kind) { printk("at24cxx_detect\n"); /* 构构一个i2c_client结构体: 以后收改数据时会用到它 */ at24cxx_client = kzalloc(sizeof(struct i2c_client), GFP_KERNEL); at24cxx_client->addr = address; at24cxx_client->adapter = adapter; if(adapter==NULL) printk("adapter not init/n"); at24cxx_client->driver = &at24cxx_driver; strcpy(at24cxx_client->name, "at24cxx"); // i2c_detect_address(at24cxx_client,0,&at24cxx_driver); major = register_chrdev(0, "at24cxx", &at24cxx_fops); cls = class_create(THIS_MODULE, "at24cxx"); clsdev=device_create(cls, NULL, MKDEV(major, 0), NULL, "at24cxx"); /* /dev/at24cxx */ return 0; } static int at24cxx_attach(struct i2c_adapter *adapter) { at24cxx_detect(adapter,addr_data.normal_i2c[0],0); return 0;//i2c_probe(adapter, &addr_data); } static int at24cxx_detach(struct i2c_adapter *adapter) { printk("at24cxx_detach\n"); device_unregister(clsdev); class_destroy(cls); unregister_chrdev(major, "at24cxx"); // i2c_detach_client(client); kfree(i2c_get_clientdata(at24cxx_client)); return 0; } /* 1. 分配一个i2c_driver结构体 */ /* 2. 设置i2c_driver结构体 */ static struct i2c_driver at24cxx_driver = { .driver = { .name = "at24cxx", }, .attach_adapter = at24cxx_attach, .detach_adapter = at24cxx_detach, .address_data = &addr_data, }; static int at24cxx_init(void) { i2c_add_driver(&at24cxx_driver); return 0; } static void at24cxx_exit(void) { i2c_del_driver(&at24cxx_driver); } module_init(at24cxx_init); module_exit(at24cxx_exit); MODULE_LICENSE("GPL");
测试代码:
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#include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> /* i2c_test r addr * i2c_test w addr val */ void print_usage(char *file) { printf("%s r addr\n", file); printf("%s w addr val\n", file); } int main(int argc, char **argv) { int fd; unsigned char buf[2]; if ((argc != 3) && (argc != 4)) { print_usage(argv[0]); return -1; } fd = open("/dev/at24cxx", O_RDWR); if (fd < 0) { printf("can't open /dev/at24cxx\n"); return -1; } if (strcmp(argv[1], "r") == 0) { buf[0] = strtoul(argv[2], NULL, 0); read(fd, buf, 1); printf("data: %c, %d, 0x%2x\n", buf[0], buf[0], buf[0]); } else if (strcmp(argv[1], "w") == 0) { buf[0] = strtoul(argv[2], NULL, 0); buf[1] = strtoul(argv[3], NULL, 0); write(fd, buf, 2); } else { print_usage(argv[0]); return -1; } return 0; }