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研发客服一、移植环境
主 机：VMWare--Fedora 9
开发板：Mini2440--64MB Nand,Kernel:2.6.30.4
编译器：arm-linux-gcc-4.3.2.tgz
u-boot：u-boot-2009.08.tar.bz2
二、移植步骤
9）实现u-boot对yaffs/yaffs2文件系统下载的支持。
注意：此篇对Nand的操作是基于MTD架构方式，在“u-boot-2009.08在2440上的移植详解（三）”中讲到过。
通常一个Nnad Flash存储设备由若干块组成，1个块由若干页组成。一般128MB以下容量的Nand Flash芯片，一页大小为528B，被依次分为2个256B的主数据区和16B的额外空间；128MB以上容量的Nand Flash芯片，一页大小通常为2KB。由于Nand Flash出现位反转的概率较大，一般在读写时需要使用ECC进行错误检验和恢复。
Yaffs/yaffs2文件系统的设计充分考虑到Nand Flash以页为存取单位等的特点，将文件组织成固定大小的段(Chunk)。以528B的页为例，Yaffs/yaffs2文件系统使用前512B存储数据和16B的额外空间存放数据的ECC和文件系统的组织信息等(称为OOB数据)。通过OOB数据，不但能实现错误检测和坏块处理，同时还可以避免加载时对整个存储介质的扫描，加快了文件系统的加载速度。以下是Yaffs/yaffs2文件系统页的结构说明：
Yaffs页结构说明
==============================================
字节 用途
==============================================
0 - 511 存储数据(分为两个半部)
512 - 515 系统信息
516 数据状态字
517 块状态字
518 - 519 系统信息
520 - 522 后半部256字节的ECC
523 - 524 系统信息
525 - 527 前半部256字节的ECC
==============================================
好了，在了解Nand Flash组成和Yaffs/yaffs2文件系统结构后，我们再回到u-boot中。目前，在u-boot中已经有对Cramfs、Jffs2等文件系统的读写支持，但与带有数据校验等功能的OOB区的Yaffs/Yaffs2文件系统相比，他们是将所有文件数据简单的以线性表形式组织的。所以，我们只要在此基础上通过修改u-boot的Nand Flash读写命令，增加处理00B区域数据的功能，即可以实现对Yaffs/Yaffs2文件系统的读写支持。
实现对Yaffs或者Yaffs2文件系统的读写支持步骤如下：
①、在include/configs/my2440.h头文件中定义一个管理对Yaffs2支持的宏和开启u-boot中对Nand Flash默认分区的宏，如下：
#gedit include/configs/my2440.h //添加到文件末尾即可
#define CONFIG_MTD_NAND_YAFFS2 1 //定义一个管理对Yaffs2支持的宏
//开启Nand Flash默认分区，注意此处的分区要和你的内核中的分区保持一致
#define MTDIDS_DEFAULT "nand0=nandflash0"
#define MTDPARTS_DEFAULT "mtdparts=nandflash0:192k(bootloader),"
"64k(params),"
"2m(kernel),"
"-(root)"
②、在原来对Nand操作的命令集列表中添加Yaffs2对Nand的写命令，如下：
接着，在该文件中对nand操作的do_nand函数中添加yaffs2对nand的操作，如下：
if (strncmp(cmd, "read", 4) == 0 || strncmp(cmd, "write", 5) == 0)
{
int read;
if (argc < 4)
goto usage;
addr = (ulong)simple_strtoul(argv[2], NULL, 16);
read = strncmp(cmd, "read", 4) == 0; /* 1 = read, 0 = write */
printf("nNAND %s: ", read ? "read" : "write");
if (arg_off_size(argc - 3, argv + 3, nand, &off, &size) != 0)
return 1;
s = strchr(cmd, '.');
if (!s || !strcmp(s, ".jffs2") || !strcmp(s, ".e") || !strcmp(s, ".i"))
{
if (read)
ret = nand_read_skip_bad(nand, off, &size, (u_char *)addr);
else
ret = nand_write_skip_bad(nand, off, &size, (u_char *)addr);
}
//添加yaffs2相关操作，注意该处又关联到nand_write_skip_bad函数
#if defined(CONFIG_MTD_NAND_YAFFS2)
else if (s != NULL && (!strcmp(s, ".yaffs2")))
{
nand->rw_oob = 1;
nand->skipfirstblk = 1;
ret = nand_write_skip_bad(nand,off,&size,(u_char *)addr);
nand->skipfirstblk = 0;
nand->rw_oob = 0;
}
#endif
else if (!strcmp(s, ".oob"))
{
/* out-of-band data */
mtd_oob_ops_t ops =
{
.oobbuf = (u8 *)addr,
.ooblen = size,
.mode = MTD_OOB_RAW
};
if (read)
ret = nand->read_oob(nand, off, &ops);
else
ret = nand->write_oob(nand, off, &ops);
}
else
{
printf("Unknown nand command suffix '%s'.n", s);
return 1;
}
printf(" %zu bytes %s: %sn", size, read ? "read" : "written", ret ? "ERROR" : "OK");
return ret == 0 ? 0 : 1;
}
③、在include/linux/mtd/mtd.h头文件的mtd_info结构体中添加上面用到rw_oob和skipfirstblk数据成员，如下：
#gedit include/linux/mtd/mtd.h //在mtd_info结构体中添加
#if defined(CONFIG_MTD_NAND_YAFFS2)
u_char rw_oob;
u_char skipfirstblk;
#endif
④、在第二步关联的nand_write_skip_bad函数中添加对Nand OOB的相关操作，如下：
#gedit drivers/mtd/nand/nand_util.c //在nand_write_skip_bad函数中添加
int nand_write_skip_bad(nand_info_t *nand, loff_t offset, size_t *length, u_char *buffer)
{
int rval;
size_t left_to_write = *length;
size_t len_incl_bad;
u_char *p_buffer = buffer;
#if defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support
if(nand->rw_oob==1)
{
size_t oobsize = nand->oobsize;
size_t datasize = nand->writesize;
int datapages = 0;
if (((*length)%(nand->oobsize+nand->writesize)) != 0)
{
printf ("Attempt to write error length data!n");
return -EINVAL;
}
datapages = *length/(datasize+oobsize);
*length = datapages*datasize;
left_to_write = *length;
}
#endif
/* Reject writes, which are not page aligned */
if ((offset & (nand->writesize - 1)) != 0 ||
(*length & (nand->writesize - 1)) != 0) {
printf ("Attempt to write non page aligned datan");
return -EINVAL;
}
len_incl_bad = get_len_incl_bad (nand, offset, *length);
if ((offset + len_incl_bad) >= nand->size) {
printf ("Attempt to write outside the flash arean");
return -EINVAL;
}
#if !defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support
if (len_incl_bad == *length) {
rval = nand_write (nand, offset, length, buffer);
if (rval != 0)
printf ("NAND write to offset %llx failed %dn",
offset, rval);
return rval;
}
#endif
while (left_to_write > 0) {
size_t block_offset = offset & (nand->erasesize - 1);
size_t write_size;
WATCHDOG_RESET ();
if (nand_block_isbad (nand, offset & ~(nand->erasesize - 1))) {
printf ("Skip bad block 0x%08llxn",
offset & ~(nand->erasesize - 1));
offset += nand->erasesize - block_offset;
continue;
}
#if defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support
if(nand->skipfirstblk==1)
{
nand->skipfirstblk=0;
printf ("Skip the first good block %llxn", offset & ~(nand->erasesize - 1));
offset += nand->erasesize - block_offset;
continue;
}
#endif
if (left_to_write < (nand->erasesize - block_offset))
write_size = left_to_write;
else
write_size = nand->erasesize - block_offset;
printf("rWriting at 0x%llx -- ",offset); //add yaffs2 file system support
rval = nand_write (nand, offset, &write_size, p_buffer);
if (rval != 0) {
printf ("NAND write to offset %llx failed %dn",