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i2c-dev.c文件完全可以被看作是一个I2C设备驱动， 不过， 它实现的i2c_client是虚拟、 临时的， 主要是为了便于从用户空间操作I2C外设。 i2c-dev.c针对每个I2C适配器生成一个主设备号为89的设备文件， 实现了i2c_driver的成员函数以及文件操作接口， 因此i2c-dev.c的主体是“i2c_driver成员函数+字符设备驱动”。
#define I2C_MAJOR 89 /* Device major number */
/*
* module load/unload record keeping
*/
static int __init i2c_dev_init(void)
{
int res;
printk(KERN_INFO "i2c /dev entries driver\n");
/* 注册一个设备号为89的主设备 */
res = register_chrdev(I2C_MAJOR, "i2c", &i2cdev_fops);
if (res)
goto out;
/* 创建一个类,自动创建设备节点 */
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;
}
/* 注册一个i2c设备驱动,当然这个设备驱动,肯定是可以支持所有的设备的 */
res = i2c_add_driver(&i2cdev_driver);
if (res)
goto out_unreg_class;
return 0;
out_unreg_class:
class_destroy(i2c_dev_class);
out_unreg_chrdev:
unregister_chrdev(I2C_MAJOR, "i2c");
out:
printk(KERN_ERR "%s: Driver Initialisation failed\n", __FILE__);
return res;
}
static void __exit i2c_dev_exit(void)
{
i2c_del_driver(&i2cdev_driver);
class_destroy(i2c_dev_class);
unregister_chrdev(I2C_MAJOR, "i2c");
}注册的主设备时，设备文件中注册了对应的操作函数。
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,
};
i2c-dev.c提供的i2cdev_read（） 、 i2cdev_write（） 函数对应于用户空间要使用的read（） 和write（）文件操作接口， 这两个函数分别调用I2C核心的i2c_master_recv（） 和i2c_master_send（） 函数来构造一条I2C消息并引发适配器Algorithm通信函数的调用， 以完成消息的传输。
具体的注册的驱动也是要万能匹配的。
static struct i2c_driver i2cdev_driver = {
.driver = {
.name = "dev_driver",
},
.attach_adapter = i2cdev_attach_adapter,
.detach_adapter = i2cdev_detach_adapter,
};
static int i2cdev_attach_adapter(struct i2c_adapter *adap)
{
struct i2c_dev *i2c_dev;
int res;
/* 创建一个i2c_dev */
i2c_dev = get_free_i2c_dev(adap);
if (IS_ERR(i2c_dev))
return PTR_ERR(i2c_dev);
/* register this i2c device with the driver core */
/* 注册一个设备到核心层 */
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;
}
/* 在sys文件系统创建操作接口 */
res = device_create_file(i2c_dev->dev, &dev_attr_name);
if (res)
goto error_destroy;
pr_debug("i2c-dev: adapter [%s] registered as minor %d\n",
adap->name, adap->nr);
return 0;
error_destroy:
device_destroy(i2c_dev_class, MKDEV(I2C_MAJOR, adap->nr));
error:
return_i2c_dev(i2c_dev);
return res;
}/*
* An i2c_dev represents an i2c_adapter ... an I2C or SMBus master, not a
* slave (i2c_client) with which messages will be exchanged. It's coupled
* with a character special file which is accessed by user mode drivers.
*
* The list of i2c_dev structures is parallel to the i2c_adapter lists
* maintained by the driver model, and is updated using notifications
* delivered to the i2cdev_driver.
*/
struct i2c_dev {
struct list_head list;
struct i2c_adapter *adap;
struct device *dev;
};
static struct i2c_dev *get_free_i2c_dev(struct i2c_adapter *adap)
{
struct i2c_dev *i2c_dev;
if (adap->nr >= I2C_MINORS) {
printk(KERN_ERR "i2c-dev: Out of device minors (%d)\n",
adap->nr);
return ERR_PTR(-ENODEV);
}
/* 申请一个设备 */
i2c_dev = kzalloc(sizeof(*i2c_dev), GFP_KERNEL);
if (!i2c_dev)
return ERR_PTR(-ENOMEM);
i2c_dev->adap = adap; /* 绑定属于这个设备的adaptor */
spin_lock(&i2c_dev_list_lock);
list_add_tail(&i2c_dev->list, &i2c_dev_list); /* 设备加入到总的设备链表 */
spin_unlock(&i2c_dev_list_lock);
return i2c_dev;这个设备的使用主要也就体现在open函数上。
因为底层主要就是几个adaptor，具体要操作那个设备，都是有
static int i2cdev_open(struct inode *inode, struct file *file)
{
unsigned int minor = iminor(inode); /* 使用次设备号来辨别设备 */
struct i2c_client *client;
struct i2c_adapter *adap;
struct i2c_dev *i2c_dev;
/* 通过次设备号(adaptor编号),找到对应的i2c_dev */
i2c_dev = i2c_dev_get_by_minor(minor);
if (!i2c_dev)
return -ENODEV;
/* 通过adaptor的编号找到adapter, 脑子有病？？ */
adap = i2c_get_adapter(i2c_dev->adap->nr);
if (!adap)
return -ENODEV;
/* This creates an anonymous i2c_client, which may later be
* pointed to some address using I2C_SLAVE or I2C_SLAVE_FORCE.
*
* This client is ** NEVER REGISTERED ** with the driver model
* or I2C core code!! It just holds private copies of addressing
* information and maybe a PEC flag.
*/
/* 申请一个客户端 */
client = kzalloc(sizeof(*client), GFP_KERNEL);
if (!client) {
i2c_put_adapter(adap);
return -ENOMEM;
}
/* 绑定这个客户端的驱动,具体的适配器以及把文件的自由数据保存为这客户端,这样使用读写函数
* 就直接可以从file的私有数据拿出来使用了
*/
snprintf(client->name, I2C_NAME_SIZE, "i2c-dev %d", adap->nr);
client->driver = &i2cdev_driver;
client->adapter = adap;
file->private_data = client;
return 0;
}
static struct i2c_dev *i2c_dev_get_by_minor(unsigned index)
{
struct i2c_dev *i2c_dev;
spin_lock(&i2c_dev_list_lock);
/* 找到设备链表上和次设备号一致的设备（adaptor） */
list_for_each_entry(i2c_dev, &i2c_dev_list, list) {
if (i2c_dev->adap->nr == index)
goto found;
}
i2c_dev = NULL;
found:
spin_unlock(&i2c_dev_list_lock);
return i2c_dev;
}
有了具体的client，那么读写函数就很简单了。这里不再重复。
static ssize_t i2cdev_read(struct file *file, char __user *buf, size_t count,
loff_t *offset)
{
char *tmp;
int ret;
struct i2c_client *client = file->private_data;
if (count > 8192)
count = 8192;
tmp = kmalloc(count, GFP_KERNEL);
if (tmp == NULL)
return -ENOMEM;
pr_debug("i2c-dev: i2c-%d reading %zu bytes.\n",
iminor(file->f_path.dentry->d_inode), count);
ret = i2c_master_recv(client, tmp, count);
if (ret >= 0)
ret = copy_to_user(buf, tmp, count) ? -EFAULT : ret;
kfree(tmp);
return ret;
}
static ssize_t i2cdev_write(struct file *file, const char __user *buf,
size_t count, loff_t *offset)
{
int ret;
char *tmp;
struct i2c_client *client = file->private_data;
if (count > 8192)
count = 8192;
tmp = kmalloc(count, GFP_KERNEL);
if (tmp == NULL)
return -ENOMEM;
if (copy_from_user(tmp, buf, count)) {
kfree(tmp);
return -EFAULT;
}
pr_debug("i2c-dev: i2c-%d writing %zu bytes.\n",
iminor(file->f_path.dentry->d_inode), count);
ret = i2c_master_send(client, tmp, count);
kfree(tmp);
return ret;
}当然这个i2cdev，也要使用ioctl来设置从机地址之类。都比较简单，这咯就不分析了
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_SLAVE: //设置从机地址
case I2C_SLAVE_FORCE:
/* NOTE: devices set up to work with "new style" drivers
* can't use I2C_SLAVE, even when the device node is not
* bound to a driver. Only I2C_SLAVE_FORCE will work.
*
* Setting the PEC flag here won't affect kernel drivers,
* which will be using the i2c_client node registered with
* the driver model core. Likewise, when that client has
* the PEC flag already set, the i2c-dev driver won't see
* (or use) this setting.
*/
/* 参数检查 */
if ((arg > 0x3ff) ||
(((client->flags & I2C_M_TEN) == 0) && arg > 0x7f))
return -EINVAL;
if (cmd == I2C_SLAVE && i2cdev_check_addr(client->adapter, arg))
return -EBUSY;
/* REVISIT: address could become busy later */
client->addr = arg; /* 设置地址 */
return 0;
case I2C_TENBIT:
if (arg)
client->flags |= I2C_M_TEN;
else
client->flags &= ~I2C_M_TEN;
return 0;
case I2C_PEC:
if (arg)
client->flags |= I2C_CLIENT_PEC;
else
client->flags &= ~I2C_CLIENT_PEC;
return 0;
case I2C_FUNCS:
/* 查询功能 */
funcs = i2c_get_functionality(client->adapter);
return put_user(funcs, (unsigned long __user *)arg);
case I2C_RDWR:
/* 直接使用ioctl设置读写 */
return i2cdev_ioctl_rdrw(client, arg);
case I2C_SMBUS:
return i2cdev_ioctl_smbus(client, arg);
case I2C_RETRIES:
client->adapter->retries = arg;
break;
case I2C_TIMEOUT:
/* For historical reasons, user-space sets the timeout
* value in units of 10 ms.
*/
client->adapter->timeout = msecs_to_jiffies(arg * 10);
break;
default:
/* NOTE: returning a fault code here could cause trouble
* in buggy userspace code. Some old kernel bugs returned
* zero in this case, and userspace code might accidentally
* have depended on that bug.
*/
return -ENOTTY;
}
return 0;
}