驱动专题:第五章MTD及Flash驱动 1.mtd框架分析
MTD(memory technology device):内存技术设备,是linux用于描述ROM,NAND,NOR等设备的子系统的抽象,MTD设备可以按块读写也可以按字节读写,也就是说MTD设备既可以是块设备也可以是字符设备,块设备(mtdblackx)操作针对文件系统,字符设备(mtdx)操作主要针对格式化等操作的测试用。
一个MTD设备的描述为mtd_info这个结构体,填充好这个结构体,然后调用add_mtd_device添加mtd设备函数就可以注册MTD设备了。在内核的源代码中,mtdram.c是一个很简单的例子,他把一块内存空间模拟了一个MTD device,研究MTD的框架,从这个mtdram.c开始:
- /*
- * mtdram - a test mtd device
- * Author: Alexander Larsson <alex@cendio.se>
- *
- * Copyright (c) 1999 Alexander Larsson <alex@cendio.se>
- * Copyright (c) 2005 Joern Engel <joern@wh.fh-wedel.de>
- *
- * This code is GPL
- *
- */
- #include <linux/module.h>
- #include <linux/slab.h>
- #include <linux/ioport.h>
- #include <linux/vmalloc.h>
- #include <linux/init.h>
- #include <linux/mtd/compatmac.h>
- #include <linux/mtd/mtd.h>
- #include <linux/mtd/mtdram.h>
- static unsigned long total_size = CONFIG_MTDRAM_TOTAL_SIZE;
- static unsigned long erase_size = CONFIG_MTDRAM_ERASE_SIZE;
- #define MTDRAM_TOTAL_SIZE (total_size * 1024)
- #define MTDRAM_ERASE_SIZE (erase_size * 1024)
- #ifdef MODULE
- module_param(total_size, ulong, 0);
- MODULE_PARM_DESC(total_size, "Total device size in KiB");
- module_param(erase_size, ulong, 0);
- MODULE_PARM_DESC(erase_size, "Device erase block size in KiB");
- #endif
- // We could store these in the mtd structure, but we only support 1 device..
- static struct mtd_info *mtd_info;
- static int ram_erase(struct mtd_info *mtd, struct erase_info *instr)
- {
- if (instr->addr + instr->len > mtd->size)
- return -EINVAL;
- memset((char *)mtd->priv + instr->addr, 0xff, instr->len);
- instr->state = MTD_ERASE_DONE;
- mtd_erase_callback(instr);
- return 0;
- }
- static int ram_point(struct mtd_info *mtd, loff_t from, size_t len,
- size_t *retlen, void **virt, resource_size_t *phys)
- {
- if (from + len > mtd->size)
- return -EINVAL;
- /* can we return a physical address with this driver? */
- if (phys)
- return -EINVAL;
- *virt = mtd->priv + from;
- *retlen = len;
- return 0;
- }
- static void ram_unpoint(struct mtd_info *mtd, loff_t from, size_t len)
- {
- }
- /*
- * Allow NOMMU mmap() to directly map the device (if not NULL)
- * - return the address to which the offset maps
- * - return -ENOSYS to indicate refusal to do the mapping
- */
- static unsigned long ram_get_unmapped_area(struct mtd_info *mtd,
- unsigned long len,
- unsigned long offset,
- unsigned long flags)
- {
- return (unsigned long) mtd->priv + offset;
- }
- static int ram_read(struct mtd_info *mtd, loff_t from, size_t len,
- size_t *retlen, u_char *buf)
- {
- if (from + len > mtd->size)
- return -EINVAL;
- memcpy(buf, mtd->priv + from, len);
- *retlen = len;
- return 0;
- }
- static int ram_write(struct mtd_info *mtd, loff_t to, size_t len,
- size_t *retlen, const u_char *buf)
- {
- if (to + len > mtd->size)
- return -EINVAL;
- memcpy((char *)mtd->priv + to, buf, len);
- *retlen = len;
- return 0;
- }
- static void __exit cleanup_mtdram(void)
- {
- if (mtd_info) {
- del_mtd_device(mtd_info);
- vfree(mtd_info->priv);
- kfree(mtd_info);
- }
- }
- int mtdram_init_device(struct mtd_info *mtd, void *mapped_address,
- unsigned long size, char *name)
- {
- memset(mtd, 0, sizeof(*mtd));
- /* Setup the MTD structure */
- mtd->name = name;
- mtd->type = MTD_RAM;
- mtd->flags = MTD_CAP_RAM;
- mtd->size = size;
- mtd->writesize = 1;
- mtd->erasesize = MTDRAM_ERASE_SIZE;
- mtd->priv = mapped_address;
- mtd->owner = THIS_MODULE;
- mtd->erase = ram_erase;
- mtd->point = ram_point;
- mtd->unpoint = ram_unpoint;
- mtd->get_unmapped_area = ram_get_unmapped_area;
- mtd->read = ram_read;
- mtd->write = ram_write;
- if (add_mtd_device(mtd)) { //填充好mtd_info之后注册这个mtd设备
- return -EIO;
- }
- return 0;
- }
- static int __init init_mtdram(void)
- {
- void *addr;
- int err;
- if (!total_size)
- return -EINVAL;
- /* Allocate some memory */
- mtd_info = kmalloc(sizeof(struct mtd_info), GFP_KERNEL); //分配mtd_info
- if (!mtd_info)
- return -ENOMEM;
- addr = vmalloc(MTDRAM_TOTAL_SIZE); //开辟一段内存用来模拟MTD设备
- if (!addr) {
- kfree(mtd_info);
- mtd_info = NULL;
- return -ENOMEM;
- }
- err = mtdram_init_device(mtd_info, addr, MTDRAM_TOTAL_SIZE, "mtdram test device");
- if (err) {
- vfree(addr);
- kfree(mtd_info);
- mtd_info = NULL;
- return err;
- }
- memset(mtd_info->priv, 0xff, MTDRAM_TOTAL_SIZE);
- return err;
- }
- module_init(init_mtdram);
- module_exit(cleanup_mtdram);
- MODULE_LICENSE("GPL");
- MODULE_AUTHOR("Alexander Larsson <alexl@redhat.com>");
- MODULE_DESCRIPTION("Simulated MTD driver for testing");
这是一个很简单的mtd设备驱动,以一块ram来模拟一个mtd设备,从上面代码可以看到,一个mtd设备的注册就是先填充好一个mtd_info,这个结构体提供设备的硬件信息以及读写擦除等操作方法。注册这个结构体就完成了一个mtd设备的添加。这里对应的是ram设备,读写是直接操作内存的,如果是nandflash和norflash设备,对读写擦除等操作函数比较复杂,但是最终mtd的设备都要调用add_mtd_device这个函数来注册,下面来分析到底这个函数做了什么来注册一个mtd设备的:
- int add_mtd_device(struct mtd_info *mtd)
- {
- int i;
- if (!mtd->backing_dev_info) {
- switch (mtd->type) {
- case MTD_RAM:
- 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);
- for (i=0; i < MAX_MTD_DEVICES; i++)
- if (!mtd_table[i]) {
- struct mtd_notifier *not;
- mtd_table[i] = mtd;
- 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);
- dev_set_name(&mtd->dev, "mtd%d", i); //设置mtd设备名称
- dev_set_drvdata(&mtd->dev, mtd);
- if (device_register(&mtd->dev) != 0) { //注册mtd设备(会自动创建mtd设备可读写的节点)
- mtd_table[i] = NULL;
- break;
- }
- if (MTD_DEVT(i))
- device_create(&mtd_class, mtd->dev.parent, //创建mtd设备只读的节点
- 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 */
- list_for_each_entry(not, &mtd_notifiers, list)
- not->add(mtd); //把这个mtd device注册到mtd
- 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;
- }
- mutex_unlock(&mtd_table_mutex);
- return 1;
- }
可以看出注册device的时候,需要调用mtd_notifiers链表里面的add函数,这个函数指针在哪里被添加进去的?
- void register_mtd_user (struct mtd_notifier *new)
- {
- int i;
- mutex_lock(&mtd_table_mutex);
- list_add(&new->list, &mtd_notifiers); //new添加到mtd_notifiers链表
- __module_get(THIS_MODULE);
- for (i=0; i< MAX_MTD_DEVICES; i++)
- if (mtd_table[i])
- new->add(mtd_table[i]);
- mutex_unlock(&mtd_table_mutex);
- }
那么register_mtd_user是谁调用的?查看代码可以知道在mtdchar.c与mtdblock.c以及mtdblock_ro.c里面注册MTD字符设备与MTD块设备的时候调用的,所以可以知道这个链表放的就是支持mtd设备的所有驱动,都放在这个链表里面,在执行add_mtd_device里面的
list_for_each_entry(not, &mtd_notifiers, list) not->add(mtd);
的时候,一个for循环调用不同驱动(字符,块,只读块驱动)的add函数来添加这个device到不同的驱动。这里以块设备驱动为例,如果添加到块驱动,那么:
- static struct mtd_notifier blktrans_notifier = {
- .add = blktrans_notify_add,
- .remove = blktrans_notify_remove,
- };
调用add就是调用:
- static void blktrans_notify_add(struct mtd_info *mtd)
- {
- struct mtd_blktrans_ops *tr;
- if (mtd->type == MTD_ABSENT)
- return;
- list_for_each_entry(tr, &blktrans_majors, list)
- tr->add_mtd(tr, mtd);
- }
可以知道执行blktrans_majors链表里面的add_mtd,这个链表的元素通过下面函数添加进去:
- int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
- {
- int ret, i;
- /* Register the notifier if/when the first device type is
- registered, to prevent the link/init ordering from fucking
- us over. */
- if (!blktrans_notifier.list.next)
- register_mtd_user(&blktrans_notifier);
- tr->blkcore_priv = kzalloc(sizeof(*tr->blkcore_priv), GFP_KERNEL);
- if (!tr->blkcore_priv)
- return -ENOMEM;
- mutex_lock(&mtd_table_mutex);
- ret = register_blkdev(tr->major, tr->name);
- if (ret) {
- printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
- tr->name, tr->major, ret);
- kfree(tr->blkcore_priv);
- mutex_unlock(&mtd_table_mutex);
- return ret;
- }
- spin_lock_init(&tr->blkcore_priv->queue_lock);
- tr->blkcore_priv->rq = blk_init_queue(mtd_blktrans_request, &tr->blkcore_priv->queue_lock);
- if (!tr->blkcore_priv->rq) {
- unregister_blkdev(tr->major, tr->name);
- kfree(tr->blkcore_priv);
- mutex_unlock(&mtd_table_mutex);
- return -ENOMEM;
- }
- tr->blkcore_priv->rq->queuedata = tr;
- blk_queue_logical_block_size(tr->blkcore_priv->rq, tr->blksize);
- if (tr->discard)
- queue_flag_set_unlocked(QUEUE_FLAG_DISCARD,
- tr->blkcore_priv->rq);
- tr->blkshift = ffs(tr->blksize) - 1;
- tr->blkcore_priv->thread = kthread_run(mtd_blktrans_thread, tr,
- "%sd", tr->name);
- if (IS_ERR(tr->blkcore_priv->thread)) {
- int ret = PTR_ERR(tr->blkcore_priv->thread);
- blk_cleanup_queue(tr->blkcore_priv->rq);
- unregister_blkdev(tr->major, tr->name);
- kfree(tr->blkcore_priv);
- mutex_unlock(&mtd_table_mutex);
- return ret;
- }
- INIT_LIST_HEAD(&tr->devs);
- list_add(&tr->list, &blktrans_majors); //添加这个块驱动到链表
- for (i=0; i<MAX_MTD_DEVICES; i++) { //注册块驱动的时候添加所有mtd的块设备
- if (mtd_table[i] && mtd_table[i]->type != MTD_ABSENT)
- tr->add_mtd(tr, mtd_table[i]);
- }
- mutex_unlock(&mtd_table_mutex);
- return 0;
- }
这个函数就是注册一个块驱动,然后添加所有mtd的块设备。所以最终的核心就是add_mtd这个,他在mtd块设备里面是mtdblock_add_mtd函数,这个函数最终会调用下面函数来添加一个MTD块设备:
- int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
- {
- struct mtd_blktrans_ops *tr = new->tr;
- struct mtd_blktrans_dev *d;
- int last_devnum = -1;
- struct gendisk *gd;
- if (mutex_trylock(&mtd_table_mutex)) {
- mutex_unlock(&mtd_table_mutex);
- BUG();
- }
- list_for_each_entry(d, &tr->devs, list) {
- if (new->devnum == -1) {
- /* Use first free number */
- if (d->devnum != last_devnum+1) {
- /* Found a free devnum. Plug it in here */
- new->devnum = last_devnum+1;
- list_add_tail(&new->list, &d->list);
- goto added;
- }
- } else if (d->devnum == new->devnum) {
- /* Required number taken */
- return -EBUSY;
- } else if (d->devnum > new->devnum) {
- /* Required number was free */
- list_add_tail(&new->list, &d->list);
- goto added;
- }
- last_devnum = d->devnum;
- }
- if (new->devnum == -1)
- new->devnum = last_devnum+1;
- if ((new->devnum << tr->part_bits) > 256) {
- return -EBUSY;
- }
- list_add_tail(&new->list, &tr->devs);
- added:
- mutex_init(&new->lock);
- if (!tr->writesect)
- new->readonly = 1;
- gd = alloc_disk(1 << tr->part_bits); //分配disk
- if (!gd) {
- list_del(&new->list);
- return -ENOMEM;
- }
- gd->major = tr->major;
- gd->first_minor = (new->devnum) << tr->part_bits;
- gd->fops = &mtd_blktrans_ops;
- if (tr->part_bits)
- if (new->devnum < 26)
- snprintf(gd->disk_name, sizeof(gd->disk_name),
- "%s%c", tr->name, 'a' + new->devnum);
- else
- snprintf(gd->disk_name, sizeof(gd->disk_name),
- "%s%c%c", tr->name,
- 'a' - 1 + new->devnum / 26,
- 'a' + new->devnum % 26);
- else
- snprintf(gd->disk_name, sizeof(gd->disk_name),
- "%s%d", tr->name, new->devnum);
- /* 2.5 has capacity in units of 512 bytes while still
- having BLOCK_SIZE_BITS set to 10. Just to keep us amused. */
- set_capacity(gd, (new->size * tr->blksize) >> 9);
- gd->private_data = new;
- new->blkcore_priv = gd;
- gd->queue = tr->blkcore_priv->rq;
- gd->driverfs_dev = &new->mtd->dev;
- if (new->readonly)
- set_disk_ro(gd, 1);
- add_disk(gd); //添加disk
- return 0;
- }
alloc_disk与add_disk这在之前分析块设备驱动框架的时候已经分析了,这两个就是注册块设备的基本函数。而如果是mtd字符设备,就会调用字符设备的添加函数,所以add_mtd_device这个函数就是这样来添加mtd设备的。
mtd设备驱动由块设备,字符设备,只读块设备等类型:
MTD块driver(针对文件系统):
- static struct mtd_blktrans_ops mtdblock_tr = {
- .name = "mtdblock",
- .major = 31,
- .part_bits = 0,
- .blksize = 512,
- .open = mtdblock_open,
- .flush = mtdblock_flush,
- .release = mtdblock_release,
- .readsect = mtdblock_readsect,
- .writesect = mtdblock_writesect,
- .add_mtd = mtdblock_add_mtd,
- .remove_dev = mtdblock_remove_dev,
- .owner = THIS_MODULE,
- };
- static int __init init_mtdblock(void)
- {
- mutex_init(&mtdblks_lock);
- return register_mtd_blktrans(&mtdblock_tr);
- }
- static void __exit cleanup_mtdblock(void)
- {
- deregister_mtd_blktrans(&mtdblock_tr);
- }
- module_init(init_mtdblock);
- module_exit(cleanup_mtdblock);
MTD字符driver(支持块设备像字符设备那样去操作,一般用作测试)
- static int __init init_mtdchar(void)
- {
- int ret;
- ret = __register_chrdev(MTD_CHAR_MAJOR, 0, 1 << MINORBITS,"mtd", &mtd_fops); //注册字符设备,捆绑mtd_fops
- if (ret < 0) {
- pr_notice("Can't allocate major number %d for Memory Technology Devices.\n", MTD_CHAR_MAJOR);
- return ret;
- }
- ret = register_filesystem(&mtd_inodefs_type); //注册mtd_inodefs_type文件系统
- if (ret) {
- pr_notice("Can't register mtd_inodefs filesystem: %d\n", ret);
- goto err_unregister_chdev;
- }
- mtd_inode_mnt = kern_mount(&mtd_inodefs_type); //挂载mtd_inodefs_type文件系统
- if (IS_ERR(mtd_inode_mnt)) {
- ret = PTR_ERR(mtd_inode_mnt);
- pr_notice("Error mounting mtd_inodefs filesystem: %d\n", ret);
- goto err_unregister_filesystem;
- }
- register_mtd_user(&mtdchar_notifier); //注册到链表
- return ret;
- err_unregister_filesystem:
- unregister_filesystem(&mtd_inodefs_type);
- err_unregister_chdev:
- __unregister_chrdev(MTD_CHAR_MAJOR, 0, 1 << MINORBITS, "mtd");
- return ret;
- }
MTD的框架跟输入子系统一样类似的分离框架,一边注册驱动(driver),一边注册设备(device),驱动有字符,块,只读块,系统开机会注册mtd设备的驱动同时添加已注册的设备。
MTD驱动端:这里可以注册mtd的字符与块设备,只读块驱动,分别对应内核代码的mtdblock.c与mtdchar.c还有只读的mtdblock_ro.c
MTD设备端:调用add_mtd_device注册设备
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