uboot2021.10-nandflash-1.nand_fill

本文只是对该函数的注释，方便之后查阅，可能有误，请高手指正。

/*** nand_fill_oob - [INTERN] Transfer client buffer to oob* @mtd: MTD device structure* @oob: oob data buffer* @len: oob data write length* @ops: oob ops structure*/
static uint8_t *nand_fill_oob(struct mtd_info *mtd, uint8_t *oob, size_t len,struct mtd_oob_ops *ops)
{struct nand_chip *chip = mtd_to_nand(mtd);/** Initialise to all 0xFF, to avoid the possibility of left over OOB* data from a previous OOB read.*/memset(chip->oob_poi, 0xff, mtd->oobsize);switch (ops->mode) {case MTD_OPS_PLACE_OOB:case MTD_OPS_RAW:memcpy(chip->oob_poi + ops->ooboffs, oob, len);return oob + len;case MTD_OPS_AUTO_OOB: {struct nand_oobfree *free = chip->ecc.layout->oobfree;uint32_t boffs = 0, woffs = ops->ooboffs;size_t bytes = 0;for (; free->length && len; free++, len -= bytes) {/* Write request not from offset 0? */if (unlikely(woffs)) {if (woffs >= free->length) {woffs -= free->length;continue;}boffs = free->offset + woffs;bytes = min_t(size_t, len,(free->length - woffs));woffs = 0;} else {bytes = min_t(size_t, len, free->length);boffs = free->offset;}memcpy(chip->oob_poi + boffs, oob, bytes);oob += bytes;}return oob;}default:BUG();}return NULL;
}

这个函数不长。

1. 首先看一下三个宏的注释

/**
* MTD operation modes
*
* @MTD_OPS_PLACE_OOB:   OOB data are placed at the given offset (default)

这个说是会把oob放置在指定的位置
* @MTD_OPS_AUTO_OOB:   OOB data are automatically placed at the free areas
*           which are defined by the internal ecclayout

这个说是把oob放置到空闲的位置，空闲位置由ecclayout指定
* @MTD_OPS_RAW:   data are transferred as-is, with no error correction;
*           this mode implies %MTD_OPS_PLACE_OOB
* 这个说，数据和它本身一致，没有ecc
* These modes can be passed to ioctl(MEMWRITE) and are also used internally.
* See notes on "MTD file modes" for discussion on %MTD_OPS_RAW vs.
* %MTD_FILE_MODE_RAW.
*/
enum {
   MTD_OPS_PLACE_OOB = 0,
   MTD_OPS_AUTO_OOB = 1,
   MTD_OPS_RAW = 2,
};

2. memset(chip->oob_poi, 0xff, mtd->oobsize);

对oob的数组填充0xff。mtd->oobsize指定缓存有多大。

3.case MTD_OPS_PLACE_OOB:
   case MTD_OPS_RAW:
       memcpy(chip->oob_poi + ops->ooboffs, oob, len);
       return oob + len;

对于以上两种情况，ops->ooboffs 指定偏移地址，oob指向存有ecc的缓存，len指定oob缓存中有的字节数。

就是，拷贝oob中的数据到chip->oob_poi这个数组中（注意下标被指定了ops->ooboffs，而可能是不为0的），拷贝的字节数为len

其中oob的值由参数传入，len的值由参数传入。

注意返回值为oob + len，是个地址值。

4. 对于自动放置的情况

case MTD_OPS_AUTO_OOB: {
       struct nand_oobfree *free = chip->ecc.layout->oobfree; //oobfree 是指的空闲区的头指针，可能不止一个
       uint32_t boffs = 0, woffs = ops->ooboffs; //起始位置
       size_t bytes = 0;

//需要考虑的情况是一个空闲区域可能写不下，所以要for循环处理。

for (; free->length && len; free++, len -= bytes) { //空闲区长度不为0，且要写的长度len不为0
           /* Write request not from offset 0? */
           if (unlikely(woffs)) { //woffs 大于 0。 //woffs取0的可能性比较大
               if (woffs >= free->length) { 大于等于,写的偏移比空闲长度大。因为指定了偏移woffs，所以要把前面的位置空出来。
                   woffs -= free->length; //减去
                   continue;
               }
               boffs = free->offset + woffs; //开始写的位置boffs，此时woffs可能还不为0，但是已经小于free->length，所以还要在偏移一点点woffs，但是这次已经落在free区间了。
               bytes = min_t(size_t, len,
                   (free->length - woffs)); //取出较小的值
               woffs = 0; //偏移清零
           } else { //woffs 等于0
               bytes = min_t(size_t, len, free->length); //对len和free->length取个小的
               boffs = free->offset; //起始位置，是free区域的起始偏移位置
           }
           memcpy(chip->oob_poi + boffs, oob, bytes); //写入字节，最大长度为bytes
           oob += bytes; //oob的指针向后移动。
       } //end for
       return oob;

} //end case

分析到此结束。

应该来说还是比较简单。