Linux设备驱动探究第1天----spi驱动（1）

本文允许转载，请注明出处：http://blog.csdn.net/fulinus

Linux内核代码实在太大了，一个小小的模块也会让你手足无措，今天下午决心要把spi驱动好好看看。

首先分析spidev.c文件，这个文件中定义struct file_operations结构中的成员。成员有spidev_write、spidev_read和spidev_ioctl，前两者实现半双工通信，后者实现全双工通信。当然还有open和release等相关的成员，先忽略吧。

spidev_write -------->spidev_sync

spidev_write -------->spidev_sync

spidev_ioctl  ------> spidev_message------->spidev_sync

详细文档见：点击打开链接

还有填充struct spi_drive数据结构体成员的函数，有spidev_probe，spidev_remove函数。以及设备驱动的初始化和退出函数：spidev_init和spidev_exit

代码分析见：点击打开链接

引用：

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define SPIDEV_MAJOR			153	//spidev主设备号
#define N_SPI_MINORS			32	/* ... up to 256 */
static DECLARE_BITMAP(minors, N_SPI_MINORS);	//声明次设备位图
#define SPI_MODE_MASK (SPI_CPHA|SPI_CPOL|SPI_CS_HIGH|SPI_LSB_FIRST|SPI_3WIRE|SPI_LOOP|SPI_NO_CS|SPI_READY)

struct spidev_data {
	dev_t	devt;				//设备号
	spinlock_t	spi_lock;		//自旋锁
	struct spi_device	*spi;	//spi设备结构体
	struct list_head	device_entry;
	struct mutex	buf_lock;	//互斥锁
	unsigned		users;		//使用者计数
	u8			*buffer;		//缓冲区
};

static LIST_HEAD(device_list);	//声明spi设备链表
static DEFINE_MUTEX(device_list_lock);	//定义互斥锁
static unsigned bufsiz = 4096;	//最大传输缓冲区大小
module_param(bufsiz, uint, S_IRUGO);
MODULE_PARM_DESC(bufsiz, "data bytes in biggest supported SPI message");

static void spidev_complete(void *arg)
{
	complete(arg);	//调用complete
}

static ssize_t spidev_sync(struct spidev_data *spidev, struct spi_message *message)
{
	DECLARE_COMPLETION_ONSTACK(done);
	int status;

	message->complete = spidev_complete;	//设置spi消息的complete方法 回调函数
	message->context = &done;

	spin_lock_irq(&spidev->spi_lock);
	if (spidev->spi == NULL)	//判断是否有指定对应的spi设备
		status = -ESHUTDOWN;
	else
		status = spi_async(spidev->spi, message);	//spi异步同步
	spin_unlock_irq(&spidev->spi_lock);

	if (status == 0) {
		wait_for_completion(&done);	//等待传输完成
		status = message->status;	//获取spi消息传输事务状态
		if (status == 0)
			status = message->actual_length;	//status等于传输的实际长度
	}
	return status;	//返回实际传输长度
}

static inline ssize_t spidev_sync_write(struct spidev_data *spidev, size_t len)
{
	struct spi_transfer	t = {
			.tx_buf		= spidev->buffer,	//发送缓冲区
			.len		= len,	//发送数据长度
		};
	struct spi_message	m;

	spi_message_init(&m);	//初始化spi消息(初始化spi传递事务队列)
	spi_message_add_tail(&t, &m);	//添加spr传递到该队列
	return spidev_sync(spidev, &m);	//同步读写
}

static inline ssize_t spidev_sync_read(struct spidev_data *spidev, size_t len)
{
	struct spi_transfer	t = {
			.rx_buf		= spidev->buffer,	//接收缓冲区
			.len		= len,	//接收数据长度
		};
	struct spi_message	m;

	spi_message_init(&m);	//初始化spi消息(初始化spi传递事务队列)
	spi_message_add_tail(&t, &m);	//添加spr传递到该队列
	return spidev_sync(spidev, &m);	//同步读写
}

static ssize_t spidev_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
{
	struct spidev_data	*spidev;
	ssize_t	status = 0;

	if (count > bufsiz)	//传输数据大于缓冲区容量
		return -EMSGSIZE;
	spidev = filp->private_data;	//从文件私有数据指针获取spidev_data
	mutex_lock(&spidev->buf_lock);	//上互斥锁
	status = spidev_sync_read(spidev, count);	//同步读,返回传输数据长度
	if (status > 0) {
		unsigned long	missing;	//丢失的数据个数
		missing = copy_to_user(buf, spidev->buffer, status);	//内核空间复制到用户空间
		if (missing == status)		//丢失的数据个数等于要传输的数据个数
			status = -EFAULT;
		else
			status = status - missing;	//传输成功的数据个数
	}
	mutex_unlock(&spidev->buf_lock);//解互斥锁
	return status;	//返回读取成功的数据个数
}

static ssize_t spidev_write(struct file *filp, const char __user *buf,size_t count, loff_t *f_pos)
{
	struct spidev_data	*spidev;
	ssize_t			status = 0;
	unsigned long		missing;

	if (count > bufsiz)	//传输数据大于缓冲区容量
		return -EMSGSIZE;
	spidev = filp->private_data;	//从文件私有数据指针获取spidev_data
	mutex_lock(&spidev->buf_lock);	//上互斥锁
	missing = copy_from_user(spidev->buffer, buf, count);	//用户空间复制到内核空间
	if (missing == 0) {	//传输失败个数为0
		status = spidev_sync_write(spidev, count);	//同步写,返回传输数据长度
	} 
	else
		status = -EFAULT;
	mutex_unlock(&spidev->buf_lock);//解互斥锁
	return status;	//返回写数据的实际个数
}

static int spidev_message(struct spidev_data *spidev,struct spi_ioc_transfer *u_xfers, unsigned n_xfers)
{
	struct spi_message	msg;
	struct spi_transfer	*k_xfers;
	struct spi_transfer	*k_tmp;
	struct spi_ioc_transfer *u_tmp;
	unsigned	n, total;
	u8	*buf;
	int	status = -EFAULT;

	spi_message_init(&msg);	//初始化spi消息(初始化spi传递事务队列)
	k_xfers = kcalloc(n_xfers, sizeof(*k_tmp), GFP_KERNEL);	//分配spi传输指针内存
	if (k_xfers == NULL)
		return -ENOMEM;
	buf = spidev->buffer;	//获取spidev_data的缓冲区
	total = 0;
	//n=xfers为spi_ioc_transfer个数,u_tmp = u_xfers为要处理的spi_ioc_transfer指针
	for (n = n_xfers, k_tmp = k_xfers, u_tmp = u_xfers;n;n--, k_tmp++, u_tmp++) {
		k_tmp->len = u_tmp->len;	//设置传输信息的长度
		total += k_tmp->len;	//累加传输信息的总长度
		if (total > bufsiz) {	//信息量超过bufsiz缓冲区最大容量
			status = -EMSGSIZE;
			goto done;
		}
		if (u_tmp->rx_buf) {	//接收缓冲区指针不为空
			k_tmp->rx_buf = buf;	//缓冲区指向buf
			if (!access_ok(VERIFY_WRITE, (u8 __user *)(uintptr_t) u_tmp->rx_buf,u_tmp->len))
				goto done;
		}
		if (u_tmp->tx_buf) {	//发送缓冲区指针不为空
			k_tmp->tx_buf = buf;	//缓冲区指针指向buf
			if (copy_from_user(buf, (const u8 __user *)(uintptr_t) u_tmp->tx_buf,u_tmp->len))	//用户空间复制数据到buf
				goto done;
		}
		buf += k_tmp->len;	//缓冲区指针移动一个传输信息的长度
		k_tmp->cs_change = !!u_tmp->cs_change;	//设置cs_change
		k_tmp->bits_per_word = u_tmp->bits_per_word;	//设置bits_per_word 一个字多少位
		k_tmp->delay_usecs = u_tmp->delay_usecs;	//设置delay_usecs 毫秒级延时
		k_tmp->speed_hz = u_tmp->speed_hz;	//设置speed_hz 速率
#ifdef VERBOSE
		dev_dbg(&spidev->spi->dev,"  xfer len %zd %s%s%s%dbits %u usec %uHz\n",
			u_tmp->len,u_tmp->rx_buf ? "rx " : "",u_tmp->tx_buf ? "tx " : "",u_tmp->cs_change ? "cs " : "",
			u_tmp->bits_per_word ? : spidev->spi->bits_per_word,u_tmp->delay_usecs,u_tmp->speed_hz ? : spidev->spi->max_speed_hz);
#endif
		spi_message_add_tail(k_tmp, &msg);	//添加spr传递到该队列
	}
	//for循环的作用是将spi_ioc_transfer批量转换为spi传递结构体spi_transfer,然后添加进spi传递事务队列
	status = spidev_sync(spidev, &msg);		//同步读写
	if (status < 0)
		goto done;
	buf = spidev->buffer;	//获取spidev_data缓冲区指针
	for (n = n_xfers, u_tmp = u_xfers; n; n--, u_tmp++) {	//批量从内核空间复制spi_ioc_transfer到用户空间
		if (u_tmp->rx_buf) {	//判断是否存在接收缓冲区
			if (__copy_to_user((u8 __user *)(uintptr_t) u_tmp->rx_buf, buf,u_tmp->len)) {
				status = -EFAULT;
				goto done;
			}
		}
		buf += u_tmp->len;	//buf指针位置调整指向下一个spi_ioc_transfer
	}
	status = total;	//status等于实际传输的数据长度
done:
	kfree(k_xfers);	//释放k_xfers
	return status;	//返回实际传输的数据长度
}

static long spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
	int	err = 0;
	int	retval = 0;
	struct spidev_data	*spidev;
	struct spi_device	*spi;
	u32	tmp;
	unsigned	n_ioc;
	struct spi_ioc_transfer	*ioc;

	if (_IOC_TYPE(cmd) != SPI_IOC_MAGIC)	//判断控制命令的类型
		return -ENOTTY;
	if (_IOC_DIR(cmd) & _IOC_READ)	//判断控制命令的方向是否为读read
		err = !access_ok(VERIFY_WRITE,(void __user *)arg, _IOC_SIZE(cmd));	//判断传输数据大小
	if (err == 0 && _IOC_DIR(cmd) & _IOC_WRITE)	//判断控制命令的方向是否为写write
		err = !access_ok(VERIFY_READ,(void __user *)arg, _IOC_SIZE(cmd));	//判断传输数据大小
	if (err)
		return -EFAULT;

	spidev = filp->private_data;	//从文件私有数据中获取spidev_data
	spin_lock_irq(&spidev->spi_lock);	//上自旋锁
	spi = spi_dev_get(spidev->spi);			//获取spi设备
	spin_unlock_irq(&spidev->spi_lock);	//解自旋锁
	if (spi == NULL)	//获取spi设备失败
		return -ESHUTDOWN;	//则返回错误
	mutex_lock(&spidev->buf_lock);	//上互斥锁
	
	switch (cmd) {
	case SPI_IOC_RD_MODE:	//设置spi读模式
		retval = __put_user(spi->mode & SPI_MODE_MASK,(__u8 __user *)arg);
		break;
	case SPI_IOC_RD_LSB_FIRST:	//设置spi读最低有效位
		retval = __put_user((spi->mode & SPI_LSB_FIRST) ?  1 : 0,(__u8 __user *)arg);
		break;
	case SPI_IOC_RD_BITS_PER_WORD:	//设置spi读每个字含多个个位
		retval = __put_user(spi->bits_per_word, (__u8 __user *)arg);
		break;
	case SPI_IOC_RD_MAX_SPEED_HZ:	//设置spi读最大速率
		retval = __put_user(spi->max_speed_hz, (__u32 __user *)arg);
		break;
	case SPI_IOC_WR_MODE:	//设置spi写模式
		retval = __get_user(tmp, (u8 __user *)arg);
		if (retval == 0) {
			u8	save = spi->mode;	//获取spi设备模式

			if (tmp & ~SPI_MODE_MASK) {
				retval = -EINVAL;
				break;
			}

			tmp |= spi->mode & ~SPI_MODE_MASK;
			spi->mode = (u8)tmp;
			retval = spi_setup(spi);	//配置spi设备
			if (retval < 0)
				spi->mode = save;
			else
				dev_dbg(&spi->dev, "spi mode %02x\n", tmp);
		}
		break;
	case SPI_IOC_WR_LSB_FIRST:	//设置spi写最低有效位
		retval = __get_user(tmp, (__u8 __user *)arg);
		if (retval == 0) {
			u8	save = spi->mode;	//获取spi设备模式

			if (tmp)
				spi->mode |= SPI_LSB_FIRST;
			else
				spi->mode &= ~SPI_LSB_FIRST;
			retval = spi_setup(spi);	//配置spi设备
			if (retval < 0)
				spi->mode = save;
			else
				dev_dbg(&spi->dev, "%csb first\n",tmp ? 'l' : 'm');
		}
		break;
	case SPI_IOC_WR_BITS_PER_WORD:	//设置spi写每个字含多个个位
		retval = __get_user(tmp, (__u8 __user *)arg);	//用户空间获取数据
		if (retval == 0) {
			u8	save = spi->bits_per_word;	//获取spi设备 每个字含多少位

			spi->bits_per_word = tmp;	//更新新的spi设备 每个字含多少位
			retval = spi_setup(spi);	//配置spi设备
			if (retval < 0)	//配置失败
				spi->bits_per_word = save;	//还原spi设备 每个字含多少位
			else
				dev_dbg(&spi->dev, "%d bits per word\n", tmp);
		}
		break;
	case SPI_IOC_WR_MAX_SPEED_HZ:		//设置spi写最大速率
		retval = __get_user(tmp, (__u32 __user *)arg);	//用户空间获取数据
		if (retval == 0) {
			u32	save = spi->max_speed_hz;	//获取spi设备最大速率

			spi->max_speed_hz = tmp;	//更新新的spi设备最大速率
			retval = spi_setup(spi);	//配置spi设备
			if (retval < 0)	//配置失败
				spi->max_speed_hz = save;	//还原spi设备最大速率
			else
				dev_dbg(&spi->dev, "%d Hz (max)\n", tmp);
		}
		break;

	default:
		//命令必须为写方向的命令,且传输数据必须是SPI_IOC_MESSAGE()修饰的命令
		if (_IOC_NR(cmd) != _IOC_NR(SPI_IOC_MESSAGE(0))|| _IOC_DIR(cmd) != _IOC_WRITE) {
			retval = -ENOTTY;
			break;
		}

		tmp = _IOC_SIZE(cmd);	//计算传输数据大小
		if ((tmp % sizeof(struct spi_ioc_transfer)) != 0) {	//判断是否为spi_ioc_transfer对齐
			retval = -EINVAL;
			break;
		}
		n_ioc = tmp / sizeof(struct spi_ioc_transfer);	//计算出spi_ioc_transfer数据的个数
		if (n_ioc == 0)
			break;

		ioc = kmalloc(tmp, GFP_KERNEL);	//分配spi_ioc_transfer指针ioc内存
		if (!ioc) {
			retval = -ENOMEM;
			break;
		}
		if (__copy_from_user(ioc, (void __user *)arg, tmp)) {	//从用户空间复制到内核空间
			kfree(ioc);	//复制失败则释放ioc内存
			retval = -EFAULT;
			break;
		}

		retval = spidev_message(spidev, ioc, n_ioc);	//spidev消息处理
		kfree(ioc);	//释放ioc内存
		break;
	}

	mutex_unlock(&spidev->buf_lock);	//解互斥锁
	spi_dev_put(spi);	//增加spi设备的引用计数
	return retval;
}

static int spidev_open(struct inode *inode, struct file *filp)
{
	struct spidev_data	*spidev;
	int	status = -ENXIO;

	mutex_lock(&device_list_lock);	//上互斥锁
	list_for_each_entry(spidev, &device_list, device_entry) {	//遍历device_list
		if (spidev->devt == inode->i_rdev) {	//判断设备号找到对应的设备
			status = 0;	//设置状态为0
			break;
		}
	}
	if (status == 0) {	//找得到对应的设备
		if (!spidev->buffer) {	//spidev_data缓冲区为空
			spidev->buffer = kmalloc(bufsiz, GFP_KERNEL);	//则分配内存
			if (!spidev->buffer) {	//还空
				dev_dbg(&spidev->spi->dev, "open/ENOMEM\n");	//调试了
				status = -ENOMEM;
			}
		}
		if (status == 0) {	//找得到对应的设备
			spidev->users++;	//spidev_data使用者计数++
			filp->private_data = spidev;	//spidev_data放在文件的私有数据里
			nonseekable_open(inode, filp);	//设置文件的打开模式(文件读写指针不会跟随读写操作移动)
		}
	} 
	else
		pr_debug("spidev: nothing for minor %d\n", iminor(inode));
	mutex_unlock(&device_list_lock);	//接互斥锁
	return status;
}

static int spidev_release(struct inode *inode, struct file *filp)
{
	struct spidev_data	*spidev;
	int	status = 0;

	mutex_lock(&device_list_lock);
	spidev = filp->private_data;	//获取spidev_data
	filp->private_data = NULL;		//清除文件的私有数据指针
	spidev->users--;				//使用者个数--
	if (!spidev->users) {	//如果使用者个数为0
		int		dofree;
		kfree(spidev->buffer);	//释放spidev_data的缓冲区内存
		spidev->buffer = NULL;	//清除spidev_data缓冲区指针
		spin_lock_irq(&spidev->spi_lock);	//上自旋锁
		dofree = (spidev->spi == NULL);	//判断spi设备是否与spidev_data解绑了
		spin_unlock_irq(&spidev->spi_lock);	//解自旋锁
		if (dofree)			//没有捆绑的spi设备
			kfree(spidev);	//则是否spidev_data内存
	}
	mutex_unlock(&device_list_lock);
	return status;
}

static const struct file_operations spidev_fops = {		//文件操作函数集
	.owner =	THIS_MODULE,
	.write =	spidev_write,		//写write
	.read =		spidev_read,		//读read
	.unlocked_ioctl = spidev_ioctl,	//控制ioctl
	.open =		spidev_open,		//打开open
	.release =	spidev_release,		//释放release
	.llseek =	no_llseek,			//文件指针移动 no_llseek表示没有移动
};

static struct class *spidev_class;

static int __devinit spidev_probe(struct spi_device *spi)
{
	struct spidev_data	*spidev;
	int	status;
	unsigned long	minor;

	spidev = kzalloc(sizeof(*spidev), GFP_KERNEL);	//分配spidev_data内存
	if (!spidev)
		return -ENOMEM;
	spidev->spi = spi;	//设置spidev_data->spi(spi设备)
	spin_lock_init(&spidev->spi_lock);
	mutex_init(&spidev->buf_lock);
	INIT_LIST_HEAD(&spidev->device_entry);	//初始化spidev_data入口链表
	mutex_lock(&device_list_lock);
	minor = find_first_zero_bit(minors, N_SPI_MINORS);	//查找次设备位图分配次设备号
	if (minor < N_SPI_MINORS) {
		struct device *dev;
		spidev->devt = MKDEV(SPIDEV_MAJOR, minor);	//计算出设备号
		//创建设备/dev/spidev%d.%d(spidev总线号.片选号)
		dev = device_create(spidev_class, &spi->dev, spidev->devt,spidev, "spidev%d.%d",spi->master->bus_num, spi->chip_select);
		status = IS_ERR(dev) ? PTR_ERR(dev) : 0;
	} 
	else {
		dev_dbg(&spi->dev, "no minor number available!\n");
		status = -ENODEV;
	}
	if (status == 0) {	//分配设备号成功
		set_bit(minor, minors);	//更新次设备位图
		list_add(&spidev->device_entry, &device_list);	//添加进设备链表
	}
	mutex_unlock(&device_list_lock);

	if (status == 0)
		spi_set_drvdata(spi, spidev);	//spi->dev->p->driver_data=spidev 
	else
		kfree(spidev);

	return status;
}

static int __devexit spidev_remove(struct spi_device *spi)
{
	struct spidev_data	*spidev = spi_get_drvdata(spi);		//根据spi设备获取spidev_data
	spin_lock_irq(&spidev->spi_lock);			//上自旋锁
	spidev->spi = NULL;								//清空spidev_data->spi指针
	spi_set_drvdata(spi, NULL);						//spi->dev->p->driver_data=NULL
	spin_unlock_irq(&spidev->spi_lock);			//解自旋锁
	mutex_lock(&device_list_lock);				//上互斥锁
	list_del(&spidev->device_entry);				//删除spidev_data入口链表
	device_destroy(spidev_class, spidev->devt);		//销毁/dev/spidev%d.%d
	clear_bit(MINOR(spidev->devt), minors);			//清除次设备位图对应位
	if (spidev->users == 0)							//使用者个数为0
		kfree(spidev);								//释放spidev_data内存
	mutex_unlock(&device_list_lock);			//解互斥锁
	return 0;
}

static struct spi_driver spidev_spi_driver = {	//spi设备驱动
	.driver = {
		.name =		"spidev",
		.owner =	THIS_MODULE,
	},
	.probe =	spidev_probe,	//spidev的probe方法(当注册了modalias域为"spidev"的spi设备或板级设备,则会调用probe方法)
	.remove =	__devexit_p(spidev_remove),	//spidev的remove方法
};

static int __init spidev_init(void)		//spidev接口初始化
{
	int status;
	BUILD_BUG_ON(N_SPI_MINORS > 256);
	//注册字符设备,主设备号SPIDEV_MAJOR=153,捆绑的设备操作函数集为spidev_fops
	status = register_chrdev(SPIDEV_MAJOR, "spi", &spidev_fops);
	if (status < 0)
		return status;
	spidev_class = class_create(THIS_MODULE, "spidev");	//创建设备类spidev_class
	if (IS_ERR(spidev_class)) {
		unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
		return PTR_ERR(spidev_class);
	}
	status = spi_register_driver(&spidev_spi_driver);	//注册spi设备驱动spidev_spi_driver
	if (status < 0) {
		class_destroy(spidev_class);
		unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
	}
	return status;
}
module_init(spidev_init);	//声明初始化入口

static void __exit spidev_exit(void)			//spidev接口销毁
{
	spi_unregister_driver(&spidev_spi_driver);	//注销spi设备驱动spidev_spi_driver
	class_destroy(spidev_class);				//注销设备类spidev_class
	unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);	//注销字符设备
}
module_exit(spidev_exit);	//声明初始化出口

MODULE_AUTHOR("Andrea Paterniani, ");
MODULE_DESCRIPTION("User mode SPI device interface");
MODULE_LICENSE("GPL");
MODULE_ALIAS("spi:spidev");

这里整理下ioctl的命令：

SPI_IOC_RD_MODE		//读 模式
SPI_IOC_RD_LSB_FIRST	//读 LSB
SPI_IOC_RD_BITS_PER_WORD	//读 每字多少位
SPI_IOC_RD_MAX_SPEED_HZ	//读 最大速率
SPI_IOC_WR_MODE		//写 模式
SPI_IOC_WR_LSB_FIRST	//写 LSB
SPI_IOC_WR_BITS_PER_WORD	//写 每字多少位
SPI_IOC_WR_MAX_SPEED_HZ	//写 最大速率
SPI_IOC_MESSAGE(n)		//传输n个数据包