i2c驱动理解

I2C驱动全面解析

Linux I2C驱动框架（超详细）

I2C驱动之i2c总线设备及驱动

 

 

 

 

 

 

 https://zhuanlan.zhihu.com/p/166124369

i2cdev_ioctl函数：

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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:     case I2C_SLAVE_FORCE:      //         if ((arg > 0x3ff) ||             (((client->flags & I2C_M_TEN) == 0) && arg > 0x7f))             return -EINVAL;         if (cmd == I2C_SLAVE && i2cdev_check_addr(client->adapter, arg)) //地址检查             return -EBUSY;         /* REVISIT: address could become busy later */         client->addr = arg;  //传从机地址给驱动         return 0;     case I2C_TENBIT:     //十位还是七位地址flag         if (arg)             client->flags |= I2C_M_TEN;         else             client->flags &= ~I2C_M_TEN;         return 0;     case I2C_PEC:       //   //设置传输后增加校验标志         /*          * 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.          */         if (arg)             client->flags |= I2C_CLIENT_PEC;         else             client->flags &= ~I2C_CLIENT_PEC;         return 0;     case I2C_FUNCS:                       funcs = i2c_get_functionality(client->adapter);     //获取适配器支持的功能 ：获取访问总线的协议，i2c协议还是smbus协议         return put_user(funcs, (unsigned long __user *)arg);       case I2C_RDWR:      //i2c数据传输         return i2cdev_ioctl_rdwr(client, arg);       case I2C_SMBUS: //smbus数据传输         return i2cdev_ioctl_smbus(client, arg);       case I2C_RETRIES:     //设置重试次数         client->adapter->retries = arg;         break;     case I2C_TIMEOUT:    //设置超时时间         /* 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; }

memdup_user（）函数：

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用户态到内核态的拷贝，都会涉及到两个必要的步骤：  *    void *memdup_user(const void __user *src, size_t len)  *    {  *        void *p;  *     *        p = kmalloc_track_caller(len, GFP_KERNEL);    //内核态分配个空间  *        if (!p)  *            return ERR_PTR(-ENOMEM);  *     *        if (copy_from_user(p, src, len)) {        //从用户态拷过来  *            kfree(p);  *            return ERR_PTR(-EFAULT);  *        }  *     *        return p;  *    }

　i2cdev_read：在主机模式，接收从机发过来的数据

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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);     //内核分配空间     if (tmp == NULL)         return -ENOMEM;       pr_debug("i2c-dev: i2c-%d reading %zu bytes.\n",         iminor(file_inode(file)), count);       ret = i2c_master_recv(client, tmp, count);    //主机接收数据     if (ret >= 0)         ret = copy_to_user(buf, tmp, count) ? -EFAULT : ret;   //将数据从内核空间拷贝到用户空间     kfree(tmp);     return ret; }

i2cdev_write：主机模式下，发送数据到从机。

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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 = memdup_user(buf, count);     //从用户空间拷贝数据到内核空间（内核空间分配+拷贝）     if (IS_ERR(tmp))         return PTR_ERR(tmp);       pr_debug("i2c-dev: i2c-%d writing %zu bytes.\n",         iminor(file_inode(file)), count);       ret = i2c_master_send(client, tmp, count);  //发数据     kfree(tmp);     return ret; }

　　

　

　

 

https://www.cnblogs.com/embInn/p/13289367.html