S3C2440驅動簡析——I2C驅動（3）

     書接上回，在討論完i2c設備、i2c適配器等初始化和刪除相應驅動的程序後，我們在這個小節把注意力放在file_operations裏面的幾個函數操作上，先貼上file_operations結構體代碼，讓我們先看看其包含了哪幾個函數。

 

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, };

 

這個結構體想必大家對其結構都相當清晰啦，由此可見，i2c驅動爲用戶空間提供的操作函數包括：

1.no_llseek

2.i2cdev_read

3.i2cdev_write

4.i2cdev_ioctl

5.i2cdev_open

6.i2cdev_release

 

下面就對它們逐一進行分析：

1.no_llseek

loff_t no_llseek(struct file *file, loff_t offset, int origin) { return -ESPIPE; }

從結構體i2cdev_fops 的成員名字llseek推測，其作用應該是改變當前I2C器件讀寫的位置，而現在正如大家所見，驅動程序並未實現這功能。

 

 

2.i2cdev_read

 

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; }

read函數主要做的事情有：

（1）struct i2c_client *client = file->private_data;

       通過參數傳入的file（在上一篇博文有闡述）而找到像對應的一個i2c設備，接下來函數就是對該設備進行操作。

（2）ret = i2c_master_recv(client, tmp, count);

       其中i2c_master_recv函數在i2c-core.c 中實現，爲了使本文結構更加清晰，故把跟硬件打交道的代碼文件i2c-core.c 放在後面的博文分析。在這裏，我們只需簡單地理解爲i2c_master_recv函數的作用是通過調用上文提及的i2c設備，並從其中提取count 字節的內容存到tmp 緩衝區裏。

（3）ret = copy_to_user(buf, tmp, count) ? -EFAULT : ret;

       若無異常情況發生，就會調用咱們非常熟悉的copy_to_user 函數，這個函數在這裏就不贅述了，建議還沒掌握的朋友查找相關資料，或者我前面的博文都有提及過，這個是基礎吖！

 

 

3.i2cdev_write

 

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); if (IS_ERR(tmp)) return PTR_ERR(tmp); 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; }

write函數又做了什麼事情呢？

（1）struct i2c_client *client = file->private_data;

       見上文read函數中的解釋。

（2）tmp = memdup_user(buf, count);

       memdup_user 函數在Util.c 中實現，源代碼如下

       void *memdup_user(const void __user *src, size_t len) { void *p; /* * Always use GFP_KERNEL, since copy_from_user() can sleep and * cause pagefault, which makes it pointless to use GFP_NOFS * or GFP_ATOMIC. */ p = kmalloc_track_caller(len, GFP_KERNEL); if (!p) return ERR_PTR(-ENOMEM); if (copy_from_user(p, src, len)) { kfree(p); return ERR_PTR(-EFAULT); } return p; }

      函數的作用一目瞭然，就是把指針src 所指向長度爲len 的內容中copy_from_user 到函數返回的指針。

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

       把緩存器tmp 裏的內容發送到設備client 。

 

 

4.i2cdev_ioctl

 

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: /* 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. */ 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; 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: funcs = i2c_get_functionality(client->adapter); return put_user(funcs, (unsigned long __user *)arg); case I2C_RDWR: 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; }

由於i2c適配器的設備節點代表的是整條i2c總線，所以在對其進行具體的文件系統操作之前還必須指明
待訪問設備的總線地址。指明地址的操作通過ioctl 系統調用完成的,它最終調用設備方法i2cdev_ioctl。ioctl函數還是採用我們非常熟悉的switch-case邏輯結構，其各種命令對應的操作分析如下

case I2C_SLAVE:
case I2C_SLAVE_FORCE: 設置從設備地址

 

case I2C_TENBIT: 設置7bit 地址 or 10bit 地址

 

case I2C_PEC: 如果I2C_PEC != 0 , to use PEC with SMBus

 

case I2C_FUNCS: 返回控制器算法所支持的傳輸種類

 

case I2C_RDWR: 執行i2cdev_ioctl_rdrw函數，代碼如下

static noinline int i2cdev_ioctl_rdrw(struct i2c_client *client, unsigned long arg) { struct i2c_rdwr_ioctl_data rdwr_arg; struct i2c_msg *rdwr_pa; u8 __user **data_ptrs; int i, res; if (copy_from_user(&rdwr_arg, (struct i2c_rdwr_ioctl_data __user *)arg, sizeof(rdwr_arg))) return -EFAULT; /* Put an arbitrary limit on the number of messages that can * be sent at once */ if (rdwr_arg.nmsgs > I2C_RDRW_IOCTL_MAX_MSGS) return -EINVAL; rdwr_pa = (struct i2c_msg *) kmalloc(rdwr_arg.nmsgs * sizeof(struct i2c_msg), GFP_KERNEL); if (!rdwr_pa) return -ENOMEM; if (copy_from_user(rdwr_pa, rdwr_arg.msgs, rdwr_arg.nmsgs * sizeof(struct i2c_msg))) { kfree(rdwr_pa); return -EFAULT; } data_ptrs = kmalloc(rdwr_arg.nmsgs * sizeof(u8 __user *), GFP_KERNEL); if (data_ptrs == NULL) { kfree(rdwr_pa); return -ENOMEM; } res = 0; for (i = 0; i < rdwr_arg.nmsgs; i++) { /* Limit the size of the message to a sane amount; * and don't let length change either. */ if ((rdwr_pa[i].len > 8192) || (rdwr_pa[i].flags & I2C_M_RECV_LEN)) { res = -EINVAL; break; } data_ptrs[i] = (u8 __user *)rdwr_pa[i].buf; rdwr_pa[i].buf = kmalloc(rdwr_pa[i].len, GFP_KERNEL); if (rdwr_pa[i].buf == NULL) { res = -ENOMEM; break; } if (copy_from_user(rdwr_pa[i].buf, data_ptrs[i], rdwr_pa[i].len)) { ++i; /* Needs to be kfreed too */ res = -EFAULT; break; } } if (res < 0) { int j; for (j = 0; j < i; ++j) kfree(rdwr_pa[j].buf); kfree(data_ptrs); kfree(rdwr_pa); return res; } res = i2c_transfer(client->adapter, rdwr_pa, rdwr_arg.nmsgs); while (i-- > 0) { if (res >= 0 && (rdwr_pa[i].flags & I2C_M_RD)) { if (copy_to_user(data_ptrs[i], rdwr_pa[i].buf, rdwr_pa[i].len)) res = -EFAULT; } kfree(rdwr_pa[i].buf); } kfree(data_ptrs); kfree(rdwr_pa); return res; }

整個函數主要做了以下幾件事

（1）copy_from_user(&rdwr_arg,
                              (struct i2c_rdwr_ioctl_data __user *)arg,
                              sizeof(rdwr_arg))

       獲得用戶傳進來的命令，並存放在rdwr_arg。

（2）copy_from_user(rdwr_pa, rdwr_arg.msgs,
                              rdwr_arg.nmsgs * sizeof(struct i2c_msg))

       把指針rdwr_pa指向結構體rdwr_arg的成員msgs。

（3）整個for循環實質就是把要進行傳輸的每個msg的信息copy到字符串指針data_ptrs當中。

（4）res = i2c_transfer(client->adapter, rdwr_pa, rdwr_arg.nmsgs);

       i2c_transfer ()函數用於進行I2C適配器和I2C設備之間的一組消息交互，i2c_transfer()函數本身不具備驅動適配器物理硬件完成消息交互的能力，它只是尋找到i2c_adapter對應的i2c_algorithm，並使用i2c_algorithm的master_xfer()函數真正驅動硬件流程。至於i2c_algorithm和master_xfer等在接下來的博文介紹。

（5）while循環裏把data_ptrs所存的信息統統copy_to_user。

case I2C_SMBUS: 執行i2cdev_ioctl_smbus 函數，主要調用i2c_smbus_xfer，函數在i2c-core.c 裏實現。在這裏我們先簡單理解此函數作用爲選擇smbus 通信協議。

case I2C_RETRIES: 設置重發次數

case I2C_TIMEOUT: 設置超時時間，設定爲 arg * 10 (ms)

呼呼~ioctl函數總算帶過了，具體沒有深入的地方，均是涉及到i2c-core.c 和數據結構i2c_algorithm的地方，這兩個東東留待接下來的博文再來收拾。

5.i2cdev_open

static int i2cdev_open(struct inode *inode, struct file *file) { unsigned int minor = iminor(inode); struct i2c_client *client; struct i2c_adapter *adap; struct i2c_dev *i2c_dev; i2c_dev = i2c_dev_get_by_minor(minor); if (!i2c_dev) return -ENODEV; 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. */ client = kzalloc(sizeof(*client), GFP_KERNEL); if (!client) { i2c_put_adapter(adap); return -ENOMEM; } snprintf(client->name, I2C_NAME_SIZE, "i2c-dev %d", adap->nr); client->driver = &i2cdev_driver; client->adapter = adap; file->private_data = client; return 0; }

最後兩個函數來點輕鬆的，一眼掃下來，就是一些註冊、初始化等工作，唯一要注意地方是這個open函數比之前所介紹的其他驅動多了一點綁定的工作，如：

client->driver = &i2cdev_driver;

client->adapter = adap;
file->private_data = client;

至於其用意，不記得的朋友建議翻看本i2c驅動系列的第一篇博文。

 

6.i2cdev_release

static int i2cdev_release(struct inode *inode, struct file *file) { struct i2c_client *client = file->private_data; i2c_put_adapter(client->adapter); kfree(client); file->private_data = NULL; return 0; }

對照着open函數來看，這個release豈不是小菜一碟？

 

 

 

    到此爲止，i2c-dev.c 的驅動代碼分析暫告一段落，由於本人水平所限，不能很深刻、到位的寫出這份驅動代碼的分析，還請各位看客多多提點。內容錯漏，請嚴厲指出！接下來本系列的第4篇博文將講述i2c-core.c 和數據結構i2c_algorithm，敬請關注！

 

本系列博文鏈接：

I2C驅動（1）http://blog.csdn.net/jarvis_xian/archive/2011/05/27/6449939.aspx
I2C驅動（2）http://blog.csdn.net/jarvis_xian/archive/2011/05/27/6451168.aspx
I2C驅動（3）http://blog.csdn.net/jarvis_xian/archive/2011/05/28/6452431.aspx
I2C驅動（4）http://blog.csdn.net/jarvis_xian/archive/2011/05/30/6455697.aspx