驅動13.i2c設備驅動程式

1 分析i2c設備的識別過程
i2c_add_driver
    i2c_register_driver
        driver->driver.bus = &i2c_bus_type;
        driver_register(&driver->driver);
        
        list_for_each_entry(adapter, &adapters, list) {
            driver->attach_adapter(adapter);
                        i2c_probe(adapter, &addr_data, eeprom_detect);
                            i2c_probe_address // 發出S信號,發出設備地址(來自addr_data)
                                i2c_smbus_xfer
                                    i2c_smbus_xfer_emulated
                                        i2c_transfer
                                            adap->algo->master_xfer // s3c24xx_i2c_xfer
                                            
        
2 怎麼寫I2C設備驅動程式？
2.1 分配一個i2c_driver結構體
2.2 設置
      attach_adapter // 它直接調用 i2c_probe(adap, 設備地址, 發現這個設備後要調用的函數);
      detach_client  // 卸載這個驅動後,如果之前發現能夠支持的設備,則調用它來清理
      
2.3 註冊：i2c_add_driver

3 寫代碼

  1 #include <linux/kernel.h>
  2 #include <linux/init.h>
  3 #include <linux/module.h>
  4 #include <linux/slab.h>
  5 #include <linux/jiffies.h>
  6 #include <linux/i2c.h>
  7 #include <linux/mutex.h>
  8 #include <linux/fs.h>
  9 #include <asm/uaccess.h>
 10 
 11 static unsigned short ignore[]      = { I2C_CLIENT_END };
 12 static unsigned short normal_addr[] = { 0x50, I2C_CLIENT_END }; /* 地址值是7位 */
 13                                         /* 改為0x60的話, 由於不存在設備地址為0x60的設備, 所以at24cxx_detect不被調用 */
 14 
 15 static unsigned short force_addr[] = {ANY_I2C_BUS, 0x60, I2C_CLIENT_END};
 16 static unsigned short * forces[] = {force_addr, NULL};
 17                                         
 18 static struct i2c_client_address_data addr_data = {
 19     .normal_i2c    = normal_addr,  /* 要發出S信號和設備地址並得到ACK信號,才能確定存在這個設備 */
 20     .probe        = ignore,
 21     .ignore        = ignore,
 22     //.forces     = forces, /* 強制認為存在這個設備 */
 23 };
 24 
 25 static struct i2c_driver at24cxx_driver;
 26 
 27 
 28 static int major;
 29 static struct class *cls;
 30 struct i2c_client *at24cxx_client;
 31 
 32 static ssize_t at24cxx_read(struct file *file, char __user *buf, size_t size, loff_t * offset)
 33 {
 34     unsigned char address;
 35     unsigned char data;
 36     struct i2c_msg msg[2];
 37     int ret;
 38     
 39     /* address = buf[0] 
 40      * data    = buf[1]
 41      */
 42     if (size != 1)
 43         return -EINVAL;
 44     
 45     copy_from_user(&address, buf, 1);
 46 
 47     /* 數據傳輸三要素: 源,目的,長度 */
 48 
 49     /* 讀AT24CXX時,要先把要讀的存儲空間的地址發給它 */
 50     msg[0].addr  = at24cxx_client->addr;  /* 目的 */
 51     msg[0].buf   = &address;              /* 源 */
 52     msg[0].len   = 1;                     /* 地址=1 byte */
 53     msg[0].flags = 0;                     /* 表示寫 */
 54 
 55     /* 然後啟動讀操作 */
 56     msg[1].addr  = at24cxx_client->addr;  /* 源 */
 57     msg[1].buf   = &data;                 /* 目的 */
 58     msg[1].len   = 1;                     /* 數據=1 byte */
 59     msg[1].flags = I2C_M_RD;                     /* 表示讀 */
 60 
 61 
 62     ret = i2c_transfer(at24cxx_client->adapter, msg, 2);
 63     if (ret == 2)
 64     {
 65         copy_to_user(buf, &data, 1);
 66         return 1;
 67     }
 68     else
 69         return -EIO;
 70 }
 71 
 72 static ssize_t at24cxx_write(struct file *file, const char __user *buf, size_t size, loff_t *offset)
 73 {
 74     unsigned char val[2];
 75     struct i2c_msg msg[1];
 76     int ret;
 77     
 78     /* address = buf[0] 
 79      * data    = buf[1]
 80      */
 81     if (size != 2)
 82         return -EINVAL;
 83     
 84     copy_from_user(val, buf, 2);
 85 
 86     /* 數據傳輸三要素: 源,目的,長度 */
 87     msg[0].addr  = at24cxx_client->addr;  /* 目的 */
 88     msg[0].buf   = val;                   /* 源 */
 89     msg[0].len   = 2;                     /* 地址+數據=2 byte */
 90     msg[0].flags = 0;                     /* 表示寫 */
 91 
 92     ret = i2c_transfer(at24cxx_client->adapter, msg, 1);
 93     if (ret == 1)
 94         return 2;
 95     else
 96         return -EIO;
 97 }
 98 
 99 
100 static struct file_operations at24cxx_fops = {
101     .owner = THIS_MODULE,
102     .read  = at24cxx_read,
103     .write = at24cxx_write,
104 };
105 
106 static int at24cxx_detect(struct i2c_adapter *adapter, int address, int kind)
107 {    
108     printk("at24cxx_detect\n");
109 
110     /* 構構一個i2c_client結構體: 以後收改數據時會用到它 */
111     at24cxx_client = kzalloc(sizeof(struct i2c_client), GFP_KERNEL);
112     at24cxx_client->addr    = address;
113     at24cxx_client->adapter = adapter;
114     at24cxx_client->driver  = &at24cxx_driver;
115     strcpy(at24cxx_client->name, "at24cxx");
116     i2c_attach_client(at24cxx_client);
117     
118     major = register_chrdev(0, "at24cxx", &at24cxx_fops);
119 
120     cls = class_create(THIS_MODULE, "at24cxx");
121     class_device_create(cls, NULL, MKDEV(major, 0), NULL, "at24cxx"); /* /dev/at24cxx */
122     
123     return 0;
124 }
125 
126 static int at24cxx_attach(struct i2c_adapter *adapter)
127 {
128     return i2c_probe(adapter, &addr_data, at24cxx_detect);
129 }
130 
131 static int at24cxx_detach(struct i2c_client *client)
132 {
133     printk("at24cxx_detach\n");
134     class_device_destroy(cls, MKDEV(major, 0));
135     class_destroy(cls);
136     unregister_chrdev(major, "at24cxx");
137 
138     i2c_detach_client(client);
139     kfree(i2c_get_clientdata(client));
140 
141     return 0;
142 }
143 
144 
145 /* 1. 分配一個i2c_driver結構體 */
146 /* 2. 設置i2c_driver結構體 */
147 static struct i2c_driver at24cxx_driver = {
148     .driver = {
149         .name    = "at24cxx",
150     },
151     .attach_adapter = at24cxx_attach,
152     .detach_client  = at24cxx_detach,
153 };
154 
155 static int at24cxx_init(void)
156 {
157     i2c_add_driver(&at24cxx_driver);
158     return 0;
159 }
160 
161 static void at24cxx_exit(void)
162 {
163     i2c_del_driver(&at24cxx_driver);
164 }
165 
166 module_init(at24cxx_init);
167 module_exit(at24cxx_exit);
168 
169 MODULE_LICENSE("GPL");