TX2440 ARM开发板Uboot移植（五、yaffs2文件系统的支持）

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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。

1、在原来对Nand操作的命令集列表中添加Yaffs2对Nand的写命令，修改 common/cmd_nand.c 文件，在U_BOOT_CMD约461行处加入读写Yaffs2格式的命令：

U_BOOT_CMD(nand, 5, 1, do_nand,
"nand    - NAND sub-system\n",
"info                  - show available NAND devices\n"
"nand device [dev]     - show or set current device\n"
"nand read[.jffs2]     - addr off|partition size\n"
"nand write[.jffs2]    - addr off|partition size - read/write `size' bytes starting\n"
"    at offset `off' to/from memory address `addr'\n"
"nand read[.yaffs2] - addr off size - read the `size' byte yaffs image starting\n"
"    at offset `off' to memory address `addr'\n"
"nand write[.yaffs2] - addr off size - write the `size' byte yaffs image starting\n"
"    at offset `off' from memory address `addr'\n"
"nand erase [clean] [off size] - erase `size' bytes from\n"
"    offset `off' (entire device if not specified)\n"
... ...

2、在该文件中，在对nand操作的do_nand函数中添加yaffs2对nand的操作：

int do_nand(cmd_tbl_t * cmdtp, int flag, int argc, char *argv[])
  ... ...
  s = strchr(cmd, '.');
  if (s != NULL && (!strcmp(s, ".jffs2") || !strcmp(s, ".e") || !strcmp(s, ".i"))) {
         。。。。。。
  } else if ( s != NULL && !strcmp(s, ".yaffs2")){
      if (read) {
        /* read */
        nand_read_options_t opts;
        memset(&opts, 0, sizeof(opts));
        opts.buffer = (u_char*) addr;
        opts.length = size;
        opts.offset = off;
        opts.readoob = 1;
        opts.quiet   = quiet;
        ret = nand_read_opts(nand, &opts);
      } else {
        /* write */
        nand_write_options_t opts;
        memset(&opts, 0, sizeof(opts));
        opts.buffer = (u_char*) addr;
        opts.length = size;
        opts.offset = off;
        /* opts.forceyaffs = 1; */
        opts.noecc = 1;
        opts.writeoob = 1;
        opts.blockalign = 1;
        opts.quiet      = quiet;
        opts.skipfirstblk = 1;
        ret = nand_write_opts(nand, &opts);
      }
    }else if (s != NULL && !strcmp(s, ".oob")) {
   /* read out-of-band data */

3、修改 include/nand.h 文件，在nand_write_options增加skipfirstblk成员：

struct nand_write_options {
u_char *buffer;  /* memory block containing image to write */
ulong length;  /* number of bytes to write */
ulong offset;  /* start address in NAND */
int quiet;  /* don't display progress messages */
int autoplace;  /* if true use auto oob layout */
int forcejffs2;  /* force jffs2 oob layout */
int forceyaffs;  /* force yaffs oob layout */
int noecc;  /* write without ecc */
int writeoob;  /* image contains oob data */
int pad;  /* pad to page size */
int blockalign;  /* 1|2|4 set multiple of eraseblocks to align to */
int skipfirstblk;
};

4、修改drivers/mtd/nand/nand_util.c文件的nand_write_opts函数，增加对skipfirstblk成员的支持：

size_t written;
int result;
int skipfirstblk = opts->skipfirstblk;
... ...
while (blockstart != (mtdoffset & (~erasesize_blockalign+1))) {
... ...
}

/* skip the first good block when wirte yaffs image*/
if(skipfirstblk){
  mtdoffset += erasesize_blockalign;
  skipfirstblk = 0;
  continue;
}

readlen = meminfo->oobblock;
... ...

5、修改drivers/mtd/nand/nand_base.c文件的nand_write_page函数，注释掉因前面设置opts.noecc=1导致烧写Nand Flash过程中出现的提示信息：

case NAND_ECC_NONE:
  //printk (KERN_WARNING "Writing data without ECC to NAND-FLASH is not recommended\n");
  this->write_buf(mtd, this->data_poi, mtd->oobblock);
  break;

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