实现u-boot对yaffs/yaffs2文件系统下载的支持

yaffs2文件系统的移植主要涉及到u-boot对yaffs2文件系统的烧写支持、linux内核对yaffs2文件系统的支持，以及yaffs2文件系统的***，现在我们按照从下到上的顺序来实现各部分的功能。
1、实现u-boot对yaffs/yaffs2文件系统下载的支持。
注意：这里对Nand的操作是基于MTD架构方式。
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u-boot对Yaffs或者Yaffs2文件系统的读写支持步骤如下：
①、在include/configs/smdk2440.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：
#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=nandflash0:256k(bootloader)," \

"128k(params)," \

"2m(kernel)," \

"-(root)"

②、在common/cmd_nand.c 原来对Nand操作的命令集列表中添加Yaffs2对Nand的写命令，如下：//在U_BOOT_CMD中添加
U_BOOT_CMD(nand, CONFIG_SYS_MAXARGS, 1, do_nand,

"NAND sub-system",

"info - show available NAND devices\n"

"nand device [dev] - show or set current device\n"

"nand read - addr off|partition size\n"

"nand write - addr off|partition size\n"

" read/write 'size' bytes starting at offset 'off'\n"

" to/from memory address 'addr', skipping bad blocks.\n"
//注意：这里只添加了yaffs2的写命令，因为我们只用u-boot下载(即写)功能，所以我们没有添加yaffs2读的命令

#if defined(CONFIG_MTD_NAND_YAFFS2)

"nand write[.yaffs2] - addr off|partition size - write `size' byte yaffs image\n"

" starting at offset off' from memory address addr' (.yaffs2 for 512+16 NAND)\n"

#endif

"nand erase [clean] [off size] - erase 'size' bytes from\n"

" offset 'off' (entire device if not specified)\n"

"nand bad - show bad blocks\n"

"nand dump[.oob] off - dump page\n"

"nand scrub - really clean NAND erasing bad blocks (UNSAFE)\n"

"nand markbad off [...] - mark bad block(s) at offset (UNSAFE)\n"

"nand biterr off - make a bit error at offset (UNSAFE)"

#ifdef CONFIG_CMD_NAND_LOCK_UNLOCK

"\n"

"nand lock [tight] [status]\n"

" bring nand to lock state or display locked pages\n"

"nand unlock [offset] [size] - unlock section"

#endif

);
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: %s\n", 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：
#if defined(CONFIG_MTD_NAND_YAFFS2)

u_char rw_oob;

u_char skipfirstblk;

#endif

④、在第二步关联的drivers/mtd/nand/nand_util.c 的nand_write_skip_bad函数中添加对Nand OOB的相关操作，如下：
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 data\n");

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 area\n");

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 %d\n",

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%08llx\n",

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 %llx\n", 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 %d\n",

offset, rval);

*length -= left_to_write;

return rval;

}
left_to_write -= write_size;

printf("%d%% is complete.",100-(left_to_write/(*length/100)));

offset += write_size;

#if defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support

if(nand->rw_oob==1)

{

p_buffer += write_size+(write_size/nand->writesize*nand->oobsize);

}

else

{

p_buffer += write_size;

}

#else

p_buffer += write_size;

#endif

}
return 0;

}
⑤、在第四步nand_write_skip_bad函数中我们看到又对nand_write函数进行了访问，所以这一步是到drivers/mtd/nand/nand_base.c 的nand_write函数中添加对yaffs2的支持，如下：
static int nand_write(struct mtd_info *mtd, loff_t to, size_t len, size_t *retlen, const uint8_t *buf)

{

struct nand_chip *chip = mtd->priv;

int ret;

#if defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support

int oldopsmode = 0;

if(mtd->rw_oob==1)

{

int i = 0;

int datapages = 0;

size_t oobsize = mtd->oobsize;

size_t datasize = mtd->writesize;

uint8_t oobtemp[oobsize];

datapages = len / (datasize);

for(i = 0; i < (datapages); i++)

{

memcpy((void *)oobtemp, (void *)(buf + datasize * (i + 1)), oobsize);

memmove((void *)(buf + datasize * (i + 1)), (void *)(buf + datasize * (i + 1) + oobsize), (datapages - (i + 1)) * (datasize) + (datapages - 1) * oobsize);

memcpy((void *)(buf+(datapages) * (datasize + oobsize) - oobsize), (void *)(oobtemp), oobsize);

}

}

#endif


/* Do not allow reads past end of device */

if ((to + len) > mtd->size)

return -EINVAL;

if (!len)

return 0;
nand_get_device(chip, mtd, FL_WRITING);
chip->ops.len = len;

chip->ops.datbuf = (uint8_t *)buf;

#if defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support

if(mtd->rw_oob!=1)

{

chip->ops.oobbuf = NULL;

}

else

{

chip->ops.oobbuf = (uint8_t *)(buf + len);

chip->ops.ooblen = mtd->oobsize;

oldopsmode = chip->ops.mode;

chip->ops.mode = MTD_OOB_RAW;

}

#else

chip->ops.oobbuf = NULL;

#endif


ret = nand_do_write_ops(mtd, to, &chip->ops);
*retlen = chip->ops.retlen;
nand_release_device(mtd);

#if defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support

chip->ops.mode = oldopsmode;

#endif


return ret;

}