应用层对i2c通用驱动接口与eeprom的i2c驱动接口从应用层到内核层调用区别和联系

来源：互联网发布：imac软件编辑：程序博客网时间：2024/05/01 01:43

一：

i2c通用接口调用过程：

i2c_dev_init--》register_chrdev(I2C_MAJOR, "i2c", &i2cdev_fops)//I2c-dev.c (drivers\i2c)

static const struct file_operations i2cdev_fops = {
.owner = THIS_MODULE,
.llseek= no_llseek,
.read = i2cdev_read,
.write = i2cdev_write,
.unlocked_ioctl= i2cdev_ioctl,
.open = i2cdev_open,
.release = i2cdev_release,
};

对一个设备操作过程如下：

应用层调用write()函数后首先进入的是i2c类设备的write函数，即i2cdev_fops中的write方法。

此处的i2cdev_fops对应的是系统中所有i2c类设备的操作。也就是说系统中所有i2c adapter 的read()

write() open() close() ioctl()等操作，首先调用的是i2c类i2cdev_fops中的方法，通过i2c类中的方法

再去寻找adapter 对应的算法i2c_algorithm，此处s3c2440对应的为s3c24xx_i2c_algorithm。

对i2c的操作方法

1.首先open

2.ioctl设置at24c02的地址

3.write()

1.open设备/dev/i2c-0

open通过系统调用最后调用到fops的i2cdev_open函数。

1 static int i2cdev_open(struct inode *inode, struct file *file)

2 {

3 。。。。。。

4 adap = i2c_get_adapter(i2c_dev->adap->nr);

5 if (!adap)

6 return -ENODEV;

8 。。。。。。

9 client = kzalloc(sizeof(*client), GFP_KERNEL);

10 if (!client) {

11 i2c_put_adapter(adap);

12 return -ENOMEM;

13 }

14 snprintf(client->name, I2C_NAME_SIZE, "i2c-dev %d", adap->nr);

15 client->driver = &i2cdev_driver;

17 client->adapter = adap;

18 file->private_data = client;

20 return 0;

21 }

可以发现此函数的作用是根据/dev/i2c-0的设备号找到对应的adapter，然后将其保存到新建的client中。

需要注意的是，此处的client与驱动中的client不同，这里的client并不会注册到总线上，和i2c驱动模型的代码无关。

此处的client只是用来保存client地址信息等。

最后将这个clietn保存到file->private_data中，供ioctl() write() open()等操作使用。

2. ioctl

应用层调用ioctl后会调用到i2cdev_ioctl()函数，此处使用的是I2C_SLAVE_FORCE，用于设置at24c02的地址。

3.write

write通过系统调用最后执行fops这中的i2cdev_write函数

[cpp] view plain

22 static ssize_t i2cdev_write(struct file *file, const char __user *buf,

23 size_t count, loff_t *offset)

24 {

25 。。。。。。

26 struct i2c_client *client = file->private_data;

27 。。。。。。

28 tmp = memdup_user(buf, count);

29 。。。。。。

30 ret = i2c_master_send(client, tmp, count);

31 。。。。。。

32 }

可以发现，在write函数中首先做的就是将在open操作中保存到file－>private_data中的client取出然后通过memdup_user函数将用户空间的缓冲区拷贝到内核空间。最后调用函数i2c_master_send()

[cpp] view plaincopy

33 int i2c_master_send(struct i2c_client *client, const char *buf, int count)

34 {

35 。。。。。。

36 ret = i2c_transfer(adap, &msg, 1);

37 。。。。。。

38 }
在i2c_mastr_send函数中首先初始化msg结构体，将client的地址、当前需要拷贝的数据长度等信息填充到msg中。最后将此msg作为形参传递给i2c_transfer函数。i2c的读写过程中，发送的信息都是

通过msg来完成的，除了device address之外。device address信息单独发送，其余的通过msg.buf来完成

并且可以发现，此处i2c_transfer中的第三个参数为1，这个参数是告诉驱动每次发送的msg个数，这里设置为1

表示每次只能发送一则msg。

i2c_transfer()函数如下：

[cpp] view plaincopy

39 int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)

40 {

41 。。。。。。

42 orig_jiffies = jiffies;

43 for (ret = 0, try = 0; try <= adap->retries; try++) {

44 ret = adap->algo->master_xfer(adap, msgs, num);

45 if (ret != -EAGAIN)

46 break;

47 if (time_after(jiffies, orig_jiffies + adap->timeout))

48 break;

49 }

50 。。。。。。

51 }

在此函数做完相关处理后直接调用adapter的algorithm来发送数据，此处即i2c-s3c2440文件中s3c24xx_i2c_probe总注册的算法

[cpp] view plaincopy

52 i2c->adap.algo = &s3c24xx_i2c_algorithm;

s3c24xx_i2c_algorithm算法具体如下：[cpp] view plaincopy

53 static const struct i2c_algorithm s3c24xx_i2c_algorithm = {

54 .master_xfer = s3c24xx_i2c_xfer,

55 .functionality = s3c24xx_i2c_func,

56 };

因此相当于直接调用了函数s3c24xx_i2c_xfers3c24xx_i2c_xfer只是对s3c24xx_i2c_doxfer的简单封装，实际的处理

都在函数s3c24xx_i2c_doxfer中。下面重点分析这个s3c24xx_i2c_doxfer函数

[cpp] view plaincopy

57 static int s3c24xx_i2c_doxfer(struct s3c24xx_i2c *i2c,

58 struct i2c_msg *msgs, int num)

59 {

60 。。。。。。

61 ret = s3c24xx_i2c_set_master(i2c);

62 。。。。。。

63 i2c->msg = msgs;

64 i2c->msg_num = num;

65 i2c->msg_ptr = 0;

66 i2c->msg_idx = 0;

67 i2c->state = STATE_START;

69 s3c24xx_i2c_enable_irq(i2c);

70 s3c24xx_i2c_message_start(i2c, msgs);

71 spin_unlock_irq(&i2c->lock);

73 timeout = wait_event_timeout(i2c->wait, i2c->msg_num == 0, HZ * 5);

74 。。。。。。

76 }

在此函数中首先调用的是s3c24xx_i2c_set_master函数，查询master(即adapter)是否

处于忙的状态。忙则休眠1ms后再次查询，总共查询400次，相当于在400ms之后i2c还处于忙状态则放弃。

master空闲后，做些相关初始化的操作。初始化操作中需要注意的是i2c->state = STATE_START，通过这个状态

位来标记i2c当前是起始状态、写状态还是读状态。

接着通关函数

[cpp] view plaincopy

77 s3c24xx_i2c_enable_irq(i2c);

打开中断。然后调用函数[cpp] view plaincopy

78 s3c24xx_i2c_message_start(i2c, msgs);

来发送第一个字节，即device address。当第一个字节发送完毕后，s3c2440的i2c控制器会产生中断。s3c2440的i2c中断发生在1.完成1字节的发送或者接收2.广播呼叫或者从地址匹配时3.总线仲裁失败。

并且当第一个字节device address发送完毕后，函数通过

[cpp] view plaincopy

79 timeout = wait_event_timeout(i2c->wait, i2c->msg_num == 0, HZ * 5);

将当前进程进入等待状态，等待处理器将msg.buf发送完毕(即i2c-msg_num==0表示发送完毕)，假如在HZ*5(5秒钟)内没有没有将msg发送完毕，则发送超时。中断处理函数在s3c24xx_i2c_probe函数注册，为s3c24xx_i2c_irq()。

s3c24xx_i2c_irq的操作很简单，最重要的一步就是调用函数i2s_s3c_irq_nextbyte。在

i2s_s3c_irq_nextbyte函数中

[cpp] view plaincopy

80 static int i2s_s3c_irq_nextbyte(struct s3c24xx_i2c *i2c, unsigned long iicstat)

81 {

82 。。。。。。

83 switch (i2c->state) {

85 。。。。。。

87 case STATE_START:

88 /* last thing we did was send a start condition on the

89 * bus, or started a new i2c message

90 */

92 if (iicstat & S3C2410_IICSTAT_LASTBIT &&

93 !(i2c->msg->flags & I2C_M_IGNORE_NAK)) {

94 /* ack was not received... */

96 dev_dbg(i2c->dev, "ack was not received\n");

97 s3c24xx_i2c_stop(i2c, -ENXIO);

98 goto out_ack;

99 }

100

101 if (i2c->msg->flags & I2C_M_RD)

102 i2c->state = STATE_READ;

103 else

104 i2c->state = STATE_WRITE;

105

106 /* terminate the transfer if there is nothing to do

107 * as this is used by the i2c probe to find devices. */

108

109 if (is_lastmsg(i2c) && i2c->msg->len == 0) {

110 dev_dbg(i2c->dev, "last msg sended\n");

111 s3c24xx_i2c_stop(i2c, 0);

112 goto out_ack;

113 }

114

115 if (i2c->state == STATE_READ)

116 goto prepare_read;

117

118 /* fall through to the write state, as we will need to

119 * send a byte as well */

120

121 case STATE_WRITE:

122 /* we are writing data to the device... check for the

123 * end of the message, and if so, work out what to do

124 */

125

126 if (!(i2c->msg->flags & I2C_M_IGNORE_NAK)) {

127 if (iicstat & S3C2410_IICSTAT_LASTBIT) {

128 dev_dbg(i2c->dev, "WRITE: No Ack\n");

129

130 s3c24xx_i2c_stop(i2c, -ECONNREFUSED);

131 goto out_ack;

132 }

133 }

134

135 retry_write:

136

137 if (!is_msgend(i2c)) {

138 byte = i2c->msg->buf[i2c->msg_ptr++];

139 writeb(byte, i2c->regs + S3C2410_IICDS);

140

141 /* delay after writing the byte to allow the

142 * data setup time on the bus, as writing the

143 * data to the register causes the first bit

144 * to appear on SDA, and SCL will change as

145 * soon as the interrupt is acknowledged */

146

147 ndelay(i2c->tx_setup);

148

149 } else if (!is_lastmsg(i2c)) {

150 /* we need to go to the next i2c message */

151

152 dev_dbg(i2c->dev, "WRITE: Next Message\n");

153

154 i2c->msg_ptr = 0;

155 i2c->msg_idx++;

156 i2c->msg++;

157

158 /* check to see if we need to do another message */

159 if (i2c->msg->flags & I2C_M_NOSTART) {

160

161 if (i2c->msg->flags & I2C_M_RD) {

162 /* cannot do this, the controller

163 * forces us to send a new START

164 * when we change direction */

165

166 s3c24xx_i2c_stop(i2c, -EINVAL);

167 }

168

169 goto retry_write;

170 } else {

171 /* send the new start */

172 s3c24xx_i2c_message_start(i2c, i2c->msg);

173 i2c->state = STATE_START;

174 }

175

176 } else {

177 /* send stop */

178

179 s3c24xx_i2c_stop(i2c, 0);

180 }

181 break;

182

183 。。。。。。

184 }

可以发现此处的函数先进入STATE_START，然后将i2c状态根据切换为读或者写状态，接着函数将需要送的字节通过代码

[cpp] view plaincopy

185 byte = i2c->msg->buf[i2c->msg_ptr++];

186 writeb(byte, i2c->regs + S3C2410_IICDS);

187

188 /* delay after writing the byte to allow the

189 * data setup time on the bus, as writing the

190 * data to the register causes the first bit

191 * to appear on SDA, and SCL will change as

192 * soon as the interrupt is acknowledged */

193

194 ndelay(i2c->tx_setup);

写到s3c2440的IICDS寄存器发送，接着又会产生中断，接着就又执行i2s_s3c_irq_nextbyte->i2s_s3c_irq_nextbyte直到msg.buf中所有的数据全部发送出去。

当所有数据发送完毕后，在i2s_s3c_irq_nextbyte函数中执行s3c24xx_i2c_stop()函数

[cpp] view plaincopy

195 static inline void s3c24xx_i2c_stop(struct s3c24xx_i2c *i2c, int ret)

196 {

197 unsigned long iicstat = readl(i2c->regs + S3C2410_IICSTAT);

198

199 dev_dbg(i2c->dev, "STOP\n");

200

201 /* stop the transfer */

202 iicstat &= ~S3C2410_IICSTAT_START;

203 writel(iicstat, i2c->regs + S3C2410_IICSTAT);

204

205 i2c->state = STATE_STOP;

206

207 s3c24xx_i2c_master_complete(i2c, ret);

208 s3c24xx_i2c_disable_irq(i2c);

209 }

在此函数中执行一些扫尾工作，并最后调用函数s3c24xx_i2c_master_complete()[cpp] view plaincopy

210 static inline void s3c24xx_i2c_master_complete(struct s3c24xx_i2c *i2c, int ret)

211 {

212 dev_dbg(i2c->dev, "master_complete %d\n", ret);

213

214 i2c->msg_ptr = 0;

215 i2c->msg = NULL;

216 i2c->msg_idx++;

217 i2c->msg_num = 0;

218 if (ret)

219 i2c->msg_idx = ret;

220

221 wake_up(&i2c->wait);

222 }

然后通过wake_up函数来唤醒等待在i2c队列上的其他操作。

到此数据写完毕。读过程类似。

二：eeprom特定接口读写

static struct i2c_driver at24_driver = {
.driver = {
.name = "at24",
.owner = THIS_MODULE,
},
.probe = at24_probe,
.remove = __devexit_p(at24_remove),
.id_table = at24_ids,
};

at24_init--》i2c_add_driver(&at24_driver)--》at24_probe-》（at24_bin_read/at24_bin_write）

[at24->bin.write = at24_bin_write;/at24->bin.read = at24_bin_read;]

二进制的文件读写与普通属性的文件读写方式大部份都一样,所不同的是.二进制文件的读写接口分别是: sysfs_dirent ->s_bin_attr.bin_attr->read和sysfs_dirent ->s_bin_attr.bin_attr->write

通过访问sysfs_create_bin_file创建sysfs系统的二进制接口文件，访问设备。

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