linux i2c驱动流程
在init中通过内核通知链bus_register_notifier 注册总线通知链
static int __init i2c_dev_init(void)
{
int res;
printk(KERN_INFO "i2c /dev entries driver\n");
res = register_chrdev_region(MKDEV(I2C_MAJOR, 0), I2C_MINORS, "i2c");
if (res)
goto out;
i2c_dev_class = class_create(THIS_MODULE, "i2c-dev");
if (IS_ERR(i2c_dev_class)) {
res = PTR_ERR(i2c_dev_class);
goto out_unreg_chrdev;
}
i2c_dev_class->dev_groups = i2c_groups;
/* Keep track of adapters which will be added or removed later */
res = bus_register_notifier(&i2c_bus_type, &i2cdev_notifier);
if (res)
goto out_unreg_class;
/* Bind to already existing adapters right away */
i2c_for_each_dev(NULL, i2cdev_attach_adapter);
return 0;
out_unreg_class:
class_destroy(i2c_dev_class);
out_unreg_chrdev:
unregister_chrdev_region(MKDEV(I2C_MAJOR, 0), I2C_MINORS);
out:
printk(KERN_ERR "%s: Driver Initialisation failed\n", __FILE__);
return res;
}
在i2cdev_attach_adapter中注册dev，分配设备号
static int i2cdev_notifier_call(struct notifier_block *nb, unsigned long action,
void *data)
{
struct device *dev = data;
switch (action) {
case BUS_NOTIFY_ADD_DEVICE:
return i2cdev_attach_adapter(dev, NULL);
case BUS_NOTIFY_DEL_DEVICE:
return i2cdev_detach_adapter(dev, NULL);
}
return 0;
}
static struct notifier_block i2cdev_notifier = {
.notifier_call = i2cdev_notifier_call,
};
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,
};
/* ------------------------------------------------------------------------- */
static struct class *i2c_dev_class;
static int i2cdev_attach_adapter(struct device *dev, void *dummy)
{
struct i2c_adapter *adap;
struct i2c_dev *i2c_dev;
int res;
if (dev->type != &i2c_adapter_type)
return 0;
adap = to_i2c_adapter(dev);
i2c_dev = get_free_i2c_dev(adap);
if (IS_ERR(i2c_dev))
return PTR_ERR(i2c_dev);
cdev_init(&i2c_dev->cdev, &i2cdev_fops);
i2c_dev->cdev.owner = THIS_MODULE;
res = cdev_add(&i2c_dev->cdev, MKDEV(I2C_MAJOR, adap->nr), 1);
if (res)
goto error_cdev;
/* register this i2c device with the driver core */
i2c_dev->dev = device_create(i2c_dev_class, &adap->dev,
MKDEV(I2C_MAJOR, adap->nr), NULL,
"i2c-%d", adap->nr);
if (IS_ERR(i2c_dev->dev)) {
res = PTR_ERR(i2c_dev->dev);
goto error;
}
pr_debug("i2c-dev: adapter [%s] registered as minor %d\n",
adap->name, adap->nr);
return 0;
error:
cdev_del(&i2c_dev->cdev);
error_cdev:
put_i2c_dev(i2c_dev);
return res;
}
最后上层在通过open 和ioctl来调用I2C设备，也可以直接在驱动中调用
调用I2C读写的方法就是去填充struct i2c_msg 这个结构体
struct i2c_msg {
__u16 addr; /* slave address */
__u16 flags;
#define I2C_M_RD 0x0001 /* read data, from slave to master */
/* I2C_M_RD is guaranteed to be 0x0001! */
#define I2C_M_TEN 0x0010 /* this is a ten bit chip address */
#define I2C_M_RECV_LEN 0x0400 /* length will be first received byte */
#define I2C_M_NO_RD_ACK 0x0800 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_IGNORE_NAK 0x1000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_REV_DIR_ADDR 0x2000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_NOSTART 0x4000 /* if I2C_FUNC_NOSTART */
#define I2C_M_STOP 0x8000 /* if I2C_FUNC_PROTOCOL_MANGLING */
__u16 len; /* msg length */
__u8 *buf; /* pointer to msg data */
};
如果在上层实现调用实际是调用ioctl 中的i2cdev_ioctl_rdwr
static long i2cdev_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct i2c_client *client = file->private_data;
unsigned long funcs;
dev_dbg(&client->adapter->dev, "ioctl, cmd=0x%02x, arg=0x%02lx\n",
cmd, arg);
switch (cmd) {
....
case I2C_RDWR:
return i2cdev_ioctl_rdwr(client, arg);
....
需要在上层传入struct i2c_rdwr_ioctl_data结构体方法如下
struct i2c_rdwr_ioctl_data {
struct i2c_msg __user *msgs; /* pointers to i2c_msgs */
__u32 nmsgs; /* number of i2c_msgs */
};
read
struct i2c_rdwr_ioctl_data work_queue;
int fd = open(dev, O_RDWR);
work_queue.nmsgs = 2;
work_queue.msgs = (struct i2c_msg *)malloc(work_queue.nmsgs * sizeof(
struct i2c_msg));
(work_queue.msgs[0]).len = 1;
(work_queue.msgs[0]).flags = 0;
(work_queue.msgs[0]).addr = slave_address;//从机地址
(work_queue.msgs[0]).buf = &w_val;//从机寄存器地址
(work_queue.msgs[1]).len = len;
(work_queue.msgs[1]).flags = I2C_M_RD;
(work_queue.msgs[1]).addr = slave_address;//从机寄存器地址
(work_queue.msgs[1]).buf = buf;//read buf
ret = ioctl(fd, I2C_RDWR, (unsigned long) &work_queue);
write
struct i2c_rdwr_ioctl_data work_queue;
unsigned char w_buf[len + 1];
w_buf[0] = reg_address;//从机寄存器地址
int fd = open(dev, O_RDWR);
work_queue.nmsgs = 1;
work_queue.msgs = (struct i2c_msg *)malloc(work_queue.nmsgs * sizeof(
struct i2c_msg));
(work_queue.msgs[0]).len = 1 + len;
(work_queue.msgs[0]).addr = slave_address;//从机地址
(work_queue.msgs[0]).buf = w_buf;
(work_queue.msgs[0]).flags = 0;
memcpy(w_buf + 1, buf, len);//要写入的buf
ret = ioctl(fd, I2C_RDWR, (unsigned long) &work_queue);
最近遇到一个I2C经常error的问题，打印hal层的的数据都是ok的，但是发现在kernel中从copy_from_user中拿到的flags是随机数，之后再hal对I2C加上bus锁解决了问题
