ARM-Linux驱动--MTD驱动分析(二)

主机：Gentoo Linux 11.2 with linux kernel 3.0.6
硬件平台：FL2440（S3C2440）with linux kernel 2.6.35
原创作品，转载请标明出处http://blog.csdn.net/yming0221/article/details/7205713

*接上文ARM-Linux驱动--MTD驱动分析(一)

1、mtd_notifier结构体

//MTD设备通知结构体
struct mtd_notifier {
	void (*add)(struct mtd_info *mtd);//加入MTD原始/字符/块设备时执行
	void (*remove)(struct mtd_info *mtd);//移除MTD原始/字符/块设备时执行
	struct list_head list;//list是双向链表，定义在include/linux/list.h
};

而struct list_head定义在/include/linux/list.h中，内核中其宏定义和函数如下

INIT_LIST_HEAD(ptr) 初始化ptr节点为表头，将前趋与后继都指向自己。
LIST_HEAD(name) 声明并初始化双向循环链表name。

static inline void __list_add(struct list_head *new, struct list_head *prev, struct list_head *next)
向链表中在prev与next之间插入元素new
static inline void list_add(struct list_head *new, struct list_head *head)
在链表中头节点后插入元素new，调用__list_add()实现。
static inline void list_add_tail(struct list_head *new, struct list_head *head)
在链表末尾插入元素new，调用__list_add()实现。

static inline void __list_del(struct list_head * prev, struct list_head * next)
删除链表中prev与next之间的元素。
static inline void list_del(struct list_head *entry)
删除链表中的元素entry。

static inline void list_del_init(struct list_head *entry)
从链表中删除元素entry,并将其初始化为新的链表。
static inline void list_move(struct list_head *list, struct list_head *head)
从链表中删除list元素，并将其加入head链表。
static inline void list_move_tail(struct list_head *list, struct list_head *head)
把list移动到链表末尾。

static inline int list_empty(const struct list_head *head)
测试链表是否为空。

static inline void __list_splice(struct list_head *list, struct list_head *head)
将链表list与head合并。
static inline void list_splice(struct list_head *list, struct list_head *head)
在list不为空的情况下，调用__list_splice()实现list与head的合并。
static inline void list_splice_init(struct list_head *list, struct list_head *head)
将两链表合并，并将list初始化。

list_entry(ptr, type, member)
list_entry的定义是怎么回事？
a. list_entry的定义在内核源文件include/linux/list.h中：
#define list_entry(ptr, type, member)
((type *)((char *)(ptr)-(unsigned long)(&((type *)0)->member)))
b. 其功能是根据list_head型指针ptr换算成其宿主结构的起始地址，该宿主结构是type型的，而ptr在其宿主结构中定义为member成员。

2、add_mtd_device函数

/**
 *	add_mtd_device - register an MTD device
 *	@mtd: pointer to new MTD device info structure
 *
 *	Add a device to the list of MTD devices present in the system, and
 *	notify each currently active MTD 'user' of its arrival. Returns
 *	zero on success or 1 on failure, which currently will only happen
 *	if there is insufficient memory or a sysfs error.
 */
//添加MTD设备函数，将MTD设备加入MTD设备链表，并通知所有的MTD user该MTD设备。返回0表示成功，返回1表示出错（内存不足或文件系统错误）
int add_mtd_device(struct mtd_info *mtd)
{
	struct mtd_notifier *not;//定义一个MTD设备通知器
	int i, error;

	//下面是设置mtd_info结构体信息
	if (!mtd->backing_dev_info) {
		switch (mtd->type) {
		case MTD_RAM://MTD_RAM定义在include/mtd/mtd-abi.h
			mtd->backing_dev_info = &mtd_bdi_rw_mappable;
			break;
		case MTD_ROM:
			mtd->backing_dev_info = &mtd_bdi_ro_mappable;
			break;
		default:
			mtd->backing_dev_info = &mtd_bdi_unmappable;
			break;
		}
	}

	BUG_ON(mtd->writesize == 0);
	mutex_lock(&mtd_table_mutex);//给操作mtd_table加锁

	do {
		if (!idr_pre_get(&mtd_idr, GFP_KERNEL))//为mtd_idr分配内存
			goto fail_locked;
		error = idr_get_new(&mtd_idr, mtd, &i);//将id号和mtd_idr关联
	} while (error == -EAGAIN);

	if (error)
		goto fail_locked;

	mtd->index = i;
	mtd->usecount = 0;

	if (is_power_of_2(mtd->erasesize))
		mtd->erasesize_shift = ffs(mtd->erasesize) - 1;
	else
		mtd->erasesize_shift = 0;

	if (is_power_of_2(mtd->writesize))
		mtd->writesize_shift = ffs(mtd->writesize) - 1;
	else
		mtd->writesize_shift = 0;

	mtd->erasesize_mask = (1 << mtd->erasesize_shift) - 1;
	mtd->writesize_mask = (1 << mtd->writesize_shift) - 1;

	/* Some chips always power up locked. Unlock them now */
	if ((mtd->flags & MTD_WRITEABLE)
	    && (mtd->flags & MTD_POWERUP_LOCK) && mtd->unlock) {
		if (mtd->unlock(mtd, 0, mtd->size))
			printk(KERN_WARNING
			       "%s: unlock failed, writes may not work\n",
			       mtd->name);
	}

	/* Caller should have set dev.parent to match the
	 * physical device.
	 */
	mtd->dev.type = &mtd_devtype;
	mtd->dev.class = &mtd_class;
	mtd->dev.devt = MTD_DEVT(i);
	//设置mtd设备名
	dev_set_name(&mtd->dev, "mtd%d", i);
	//设置mtd设备信息mtd_info
	dev_set_drvdata(&mtd->dev, mtd);
	
	//注册设备
	if (device_register(&mtd->dev) != 0)
		goto fail_added;

	//创建设备
	if (MTD_DEVT(i))
		device_create(&mtd_class, mtd->dev.parent,
			      MTD_DEVT(i) + 1,
			      NULL, "mtd%dro", i);

	DEBUG(0, "mtd: Giving out device %d to %s\n", i, mtd->name);
	/* No need to get a refcount on the module containing
	   the notifier, since we hold the mtd_table_mutex */
	//遍历list链表将每个mtd_notifier执行add()函数，对新加入的mtd设备操作，通知所有的MTD user新的MTD设备的到来
	list_for_each_entry(not, &mtd_notifiers, list)
		not->add(mtd);

	//解锁信号量
	mutex_unlock(&mtd_table_mutex);
	/* We _know_ we aren't being removed, because
	   our caller is still holding us here. So none
	   of this try_ nonsense, and no bitching about it
	   either. :) */
	__module_get(THIS_MODULE);
	return 0;

fail_added:
	idr_remove(&mtd_idr, i);
fail_locked:
	mutex_unlock(&mtd_table_mutex);
	return 1;
}

其中用到的IDR机制如下：

(1)获得idr
要在代码中使用idr，首先要包括<linux/idr.h>。接下来，我们要在代码中分配idr结构体，并初始化：
void idr_init(struct idr *idp);
其中idr定义如下：
struct idr {
struct idr_layer *top;
struct idr_layer *id_free;
int layers;
int id_free_cnt;
spinlock_t lock;
};
/* idr是idr机制的核心结构体 */
(2)为idr分配内存
int idr_pre_get(struct idr *idp, unsigned int gfp_mask);
每次通过idr获得ID号之前，需要先分配内存。
返回0表示错误，非零值代表正常
(3)分配ID号并将ID号和指针关联
int idr_get_new(struct idr *idp, void *ptr, int *id);
int idr_get_new_above(struct idr *idp, void *ptr, int start_id, int *id);
idp: 之前通过idr_init初始化的idr指针
id: 由内核自动分配的ID号
ptr: 和ID号相关联的指针
start_id: 起始ID号。内核在分配ID号时，会从start_id开始。如果为I2C节点分配ID号，可以将设备地址作为start_id
函数调用正常返回0，如果没有ID可以分配，则返回-ENOSPC
在实际中，上述函数常常采用如下方式使用：
again:
if (idr_pre_get(&my_idr, GFP_KERNEL) == 0) {
/* No memory, give up entirely */
}
spin_lock(&my_lock);
result = idr_get_new(&my_idr, &target, &id);
if (result == -EAGAIN) {
sigh();
spin_unlock(&my_lock);
goto again;
}
(4)通过ID号搜索对应的指针
void *idr_find(struct idr *idp, int id);
返回值是和给定id相关联的指针，如果没有，则返回NULL
(5)删除ID
要删除一个ID，使用：
void idr_remove(struct idr *idp, int id);
通过上面这些方法，内核代码可以为子设备，inode生成对应的ID号。这些函数都定义在lib/idr.c中

3、del_mtd_device函数

/**
 *	del_mtd_device - unregister an MTD device
 *	@mtd: pointer to MTD device info structure
 *
 *	Remove a device from the list of MTD devices present in the system,
 *	and notify each currently active MTD 'user' of its departure.
 *	Returns zero on success or 1 on failure, which currently will happen
 *	if the requested device does not appear to be present in the list.
 */
//删除mtd设备函数。
//从MTD设备的链表中移除该MTD设备信息，并通知系统中所有的MTD user该MTD设备的移除。
//返回0表示成功，返回1表示出错（该设备信息不存在设备链表中）
int del_mtd_device (struct mtd_info *mtd)
{
	int ret;
	struct mtd_notifier *not;//定义一个mtd_notifier指针

	mutex_lock(&mtd_table_mutex);

	if (idr_find(&mtd_idr, mtd->index) != mtd) {
		ret = -ENODEV;
		goto out_error;
	}

	/* No need to get a refcount on the module containing
		the notifier, since we hold the mtd_table_mutex */
	//遍历list链表，并使每个mtd_notifier执行remove函数，通知每个MTD user该设备的移除
	list_for_each_entry(not, &mtd_notifiers, list)
		not->remove(mtd);

	if (mtd->usecount) {
		printk(KERN_NOTICE "Removing MTD device #%d (%s) with use count %d\n",
		       mtd->index, mtd->name, mtd->usecount);
		ret = -EBUSY;
	} else {
		device_unregister(&mtd->dev);//移除MTD设备

		idr_remove(&mtd_idr, mtd->index);//移除mtd的id号并释放已分配的内存

		module_put(THIS_MODULE);
		ret = 0;
	}

out_error:
	mutex_unlock(&mtd_table_mutex);
	return ret;
}

4、register_mtd_user函数

/**
 *	register_mtd_user - register a 'user' of MTD devices.
 *	@new: pointer to notifier info structure
 *
 *	Registers a pair of callbacks function to be called upon addition
 *	or removal of MTD devices. Causes the 'add' callback to be immediately
 *	invoked for each MTD device currently present in the system.
 */
//MTD原始设备使用者注册MTD设备（具体的字符设备或块设备）
//参数是新的mtd通知器，将其加入mtd_notifiers队列，然后
void register_mtd_user (struct mtd_notifier *new)
{
	struct mtd_info *mtd;

	mutex_lock(&mtd_table_mutex);

	//将new->list头插mtd_notifiers入链表
	list_add(&new->list, &mtd_notifiers);

 	__module_get(THIS_MODULE);

	//对每个MTD原始设备执行add函数
	mtd_for_each_device(mtd)
		new->add(mtd);

	mutex_unlock(&mtd_table_mutex);
}

5、unregister_mtd_user函数

/**
 *	unregister_mtd_user - unregister a 'user' of MTD devices.
 *	@old: pointer to notifier info structure
 *
 *	Removes a callback function pair from the list of 'users' to be
 *	notified upon addition or removal of MTD devices. Causes the
 *	'remove' callback to be immediately invoked for each MTD device
 *	currently present in the system.
 */
//删除MTD设备。
//通知所有该MTD原始设备的MTD设备执行remove()函数，将被删除的MTD设备的通知器从mtd_notifier队列中删除
int unregister_mtd_user (struct mtd_notifier *old)
{
	struct mtd_info *mtd;

	mutex_lock(&mtd_table_mutex);

	module_put(THIS_MODULE);

	//通知所有该MTD原始设备的MTD设备执行remove()函数
	mtd_for_each_device(mtd)
		old->remove(mtd);

	//将被删除的MTD设备的通知器从mtd_notifier队列中删除
	list_del(&old->list);
	mutex_unlock(&mtd_table_mutex);
	return 0;
}

6、获取MTD设备的操作指针，只是参数不同，一个是按照设备地址，另一个是安装设备的名称来获取MTD设备的操作地址

struct mtd_info *get_mtd_device(struct mtd_info *mtd, int num)

struct mtd_info *get_mtd_device_nm(const char *name)

下面现分析第一个函数

/**
 *	get_mtd_device - obtain a validated handle for an MTD device
 *	@mtd: last known address of the required MTD device
 *	@num: internal device number of the required MTD device
 *
 *	Given a number and NULL address, return the num'th entry in the device
 *	table, if any.	Given an address and num == -1, search the device table
 *	for a device with that address and return if it's still present. Given
 *	both, return the num'th driver only if its address matches. Return
 *	error code if not.
 */
//根据设备地址来获取MTD设备的操作地址
struct mtd_info *get_mtd_device(struct mtd_info *mtd, int num)
{
	struct mtd_info *ret = NULL, *other;
	int err = -ENODEV;

	//给mtd_table加锁，以便互斥访问
	mutex_lock(&mtd_table_mutex);

	if (num == -1) {//num=-1&&链表不空，则返回mtd的地址
		mtd_for_each_device(other) {
			if (other == mtd) {
				ret = mtd;
				break;
			}
		}
	} else if (num >= 0) {//num>=0，查找第num个设备，若不空，返回地址，若为空，返回NULL
		ret = idr_find(&mtd_idr, num);
		if (mtd && mtd != ret)
			ret = NULL;
	}

	if (!ret) {
		ret = ERR_PTR(err);
		goto out;
	}

	err = __get_mtd_device(ret);
	//错误处理
	if (err)
		ret = ERR_PTR(err);
out:
	mutex_unlock(&mtd_table_mutex);//解锁互斥信号量
	return ret;
}


int __get_mtd_device(struct mtd_info *mtd)
{
	int err;

	if (!try_module_get(mtd->owner))
		return -ENODEV;

	if (mtd->get_device) {

		err = mtd->get_device(mtd);

		if (err) {
			module_put(mtd->owner);
			return err;
		}
	}
	mtd->usecount++;//增加该MTD原始设备的使用者计数器
	return 0;
}

第二个函数

/**
 *	get_mtd_device_nm - obtain a validated handle for an MTD device by
 *	device name
 *	@name: MTD device name to open
 *
 * 	This function returns MTD device description structure in case of
 * 	success and an error code in case of failure.
 */
//通过设备名来获得相应的MTD原始设备的操作地址
//该函数和上面的函数类似，不过就是通过循环比较MTD设备的name字段来返回
struct mtd_info *get_mtd_device_nm(const char *name)
{
	int err = -ENODEV;
	struct mtd_info *mtd = NULL, *other;

	mutex_lock(&mtd_table_mutex);

	mtd_for_each_device(other) {
		if (!strcmp(name, other->name)) {
			mtd = other;
			break;
		}
	}

	if (!mtd)
		goto out_unlock;

	if (!try_module_get(mtd->owner))
		goto out_unlock;

	if (mtd->get_device) {
		err = mtd->get_device(mtd);
		if (err)
			goto out_put;
	}

	mtd->usecount++;
	mutex_unlock(&mtd_table_mutex);
	return mtd;

out_put:
	module_put(mtd->owner);
out_unlock:
	mutex_unlock(&mtd_table_mutex);
	return ERR_PTR(err);
}

下篇分析MTD原始设备的分区实现方法ARM-Linux驱动--MTD驱动分析(三)