原文地址:
http://blog.csdn.net/wang_zheng_kai/article/details/19039273
六、驱动层之Flash读操作
MTD对NAND芯片的读写 主要分三部分:
A、struct mtd_info中的读写函数,如read,write_oob等,这是MTD原始设备层与FLASH硬件层之间的接口;
B、struct nand_ecc_ctrl中的读写函数,如read_page_raw,write_page等,主要用来做一些与ecc有关的操作;
C、struct nand_chip中的读写函数,如read_buf,cmdfunc等,与具体的NANDcontroller相关,就是这部分函数与硬件交互,通常需要我们自己来实现。
注: nand_chip中的读写函数虽然与具体的NAND controller相关,但是MTD也为我们提供了默认的读写函数,如果NAND controller比较通用(使用PIO模式),那么对NAND芯片的读写与MTD提供的这些函数一致,就不必自己实现这些函数。
上面三部分读写函数相互配合完成对NAND芯片的读写,具体流程如下:
首先,MTD上层需要读写NAND芯片时,会调用struct mtd_info中的读写函数,接着struct mtd_info中的读写函数就会调用struct nand_chip或struct nand_ecc_ctrl中的读写函数,最后,若调用的是struct nand_ecc_ctrl中的读写函数,那么它又会接着调用struct nand_chip中的读写函数。
以读为例:
MTD上层会调用struct mtd_info中的读page函数,即nand_read函数。
接着nand_read函数会调用struct nand_chip中cmdfunc函数,这个cmdfunc函数与具体的NAND controller相关,它的作用是使NAND controller向NAND芯片发出读命令,NAND芯片收到命令后,就会做好准备等待NAND controller下一步的读取。接着nand_read函数又会调用struct nand_ecc_ctrl中的read_page函数,而read_page函数又会调用struct nand_chip中read_buf函数,从而真正把NAND芯片中的数据读取到buffer中(所以这个read_buf的意思其实应该是read into buffer,另外,这个buffer是struct mtd_info中的nand_read函数传下来的)。
read_buf函数返回后,read_page函数就会对buffer中的数据做一些处理,比如校验ecc,以及若数据有错,就根据ecc对数据修正之类的,最后read_page函数返回到nand_read函数中。
对NAND芯片的其它操作,如写,擦除等,都与读操作类似
JZ4780之NAND FLASH读函数调用流程:
mtd上层选中并调用mtd_info中的读函数
->nand_read(mtd_info)
->nand_do_read_ops
(1)->chip->cmdfunc(mtd,NAND_CMD_READ0, 0x00, page);
(2)->chip->ecc.read_page()
(1) -> read_buf()(read into buffer)
(2) -> 调用一系列函数进行相关的ecc校验
问题:nand_chip(nand flash的描述符)的读写操作是怎么和MTD的读写操作联系起来的呢?
1)probe->scan_tail;
在填充MTD的时候,使用mtd->read = nand_read;这里和mtd挂钩。
2)在nand_read实现中又调用了nand_do_read_ops(mtd,from, &chip->ops);这里和nand_chip联系起来了。
以读为例对代码进行分析如下:
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读分析
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MTD 读取数据的入口是 nand_read,然后调用 nand_do_read_ops,此函数主体如下:
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《一》nand_read代码如下:
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static int nand_read(struct mtd_info *mtd, loff_t from, size_t len,
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size_tsize_t *retlen, uint8_t *buf)
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{
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struct mtd_oob_ops ops;
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int ret;
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nand_get_device(mtd, FL_READING);
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ops.len = len;
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ops.datbuf = buf;
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ops.oobbuf = NULL;
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ops.mode = MTD_OPS_PLACE_OOB;
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ret = nand_do_read_ops(mtd, from, &ops);
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*retlen = ops.retlen;
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nand_release_device(mtd);
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return ret;
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}
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《二》nand_do_read_ops代码如下:
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static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
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struct mtd_oob_ops *ops)
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{
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/******省略****/
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。。。。。。。。。。。。。。
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while(1) {
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/******省略****/
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.。。。。。。。。。。。。。。。
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if (likely(sndcmd)) {/*#define NAND_CMD_READ0 0*/
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/*1)***读取数据前肯定要先发送对应的读页命令******/
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chip->cmdfunc(mtd, NAND_CMD_READ0, 0x00, page);
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sndcmd = 0;
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}
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/* Now read the page into the buffer */
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if (unlikely(ops->mode == MTD_OOB_RAW))
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ret = chip->ecc.read_page_raw(mtd, chip,bufpoi, page);
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else if (!aligned && NAND_SUBPAGE_READ(chip) && !oob)
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ret = chip->ecc.read_subpage(mtd, chip, col, bytes, bufpoi);
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else
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/******执行到这里read_page函数读取对应的数据了******/
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ret = chip->ecc.read_page(mtd, chip, bufpoi,page);
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if (ret < 0)
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break;
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/* Transfer not aligned data */
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if (!aligned) {
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if (!NAND_SUBPAGE_READ(chip) && !oob)
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chip->pagebuf = realpage;
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memcpy(buf, chip->buffers->databuf + col, bytes);
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}
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buf += bytes;
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。。。。。。。。。。。。。。。。。。
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if (mtd->ecc_stats.failed - stats.failed)
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return -EBADMSG;
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return mtd->ecc_stats.corrected - stats.corrected ? -EUCLEAN : 0;
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}
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上面这些代码都不需要我们去实现的,使用MTD层的自定义代码就行。下面将要分析chip->cmdfunc,我们从probe函数中可以知道
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/* step3. replace NAND command function with large page version */
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if (mtd->writesize > 512)
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chip->cmdfunc = jz4780_nand_command_lp;
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jz4780_nand_command_lp的分析
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static void jz4780_nand_command_lp(struct mtd_info *mtd,
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unsigned int command, int column, int page_addr)
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{
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register struct nand_chip *chip = mtd->priv;
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struct jz4780_nand *nand;
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nand_flash_if_t *nand_if;
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nand_flash_info_t *nand_info;
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nand = mtd_to_jz4780_nand(mtd);
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nand_if = nand->nand_flash_if_table[nand->curr_nand_flash_if];
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nand_if->curr_command = command;
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nand_info = nand->curr_nand_flash_info;
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/* Emulate NAND_CMD_READOOB */
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if (command == NAND_CMD_READOOB) {
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column += mtd->writesize;
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command = NAND_CMD_READ0;
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}
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/* Command latch cycle */
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/* 此处就是就是发送读命令的第一个周期1st Cycle的命令,即0x00, 对应着上述步骤中的① */
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chip->cmd_ctrl(mtd, command & 0xff,
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NAND_NCE | NAND_CLE | NAND_CTRL_CHANGE);
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jz4780_nand_delay_after_command(nand, nand_info, command);
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if (column != -1 || page_addr != -1) {
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int ctrl = NAND_CTRL_CHANGE | NAND_NCE | NAND_ALE;
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/* Serially input address */
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/* 发送两个column列地址,对应着上述步骤中的② */
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if (column != -1) {
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chip->cmd_ctrl(mtd, column, ctrl);
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ctrl &= ~NAND_CTRL_CHANGE;
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chip->cmd_ctrl(mtd, column >> 8, ctrl);
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}
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if (page_addr != -1) {
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/* 接下来是发送三个Row,行地址,对应着上述步骤中的② */
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chip->cmd_ctrl(mtd, page_addr, ctrl);
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chip->cmd_ctrl(mtd, page_addr >> 8,
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NAND_NCE | NAND_ALE);
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/* One more address cycle for devices > 128MiB */
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if (chip->chipsize > (128 << 20))
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chip->cmd_ctrl(mtd, page_addr >> 16,
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NAND_NCE | NAND_ALE);
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}
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}
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jz4780_nand_delay_after_address(nand, nand_info, command);
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chip->cmd_ctrl(mtd, NAND_CMD_NONE, NAND_NCE | NAND_CTRL_CHANGE);
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switch (command) {
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。。。。。。。。。。。。。。。
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/******省略****/
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.。。。。。。。。。。。。。。。
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/* 接下来发送读命令的第二个周期2nd Cycle的命令,即0x30,对应着 上述步骤中的④ */
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case NAND_CMD_READ0:
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chip->cmd_ctrl(mtd, NAND_CMD_READSTART,
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NAND_NCE | NAND_CLE | NAND_CTRL_CHANGE);
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chip->cmd_ctrl(mtd, NAND_CMD_NONE,
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NAND_NCE | NAND_CTRL_CHANGE);
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/* This applies to read commands */
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default:
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/*
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* If we don't have access to the busy pin, we apply the given
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* command delay.
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*/
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if (!chip->dev_ready) {
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nand->udelay(chip->chip_delay);
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return;
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}
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}
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/*
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* Apply this short delay always to ensure that we do wait tWB in
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* any case on any machine.
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*/
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/* 此处是对应着④中的tWB的等待时间*/
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nand->ndelay(100);
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/* 接下来就是要等待一定的时间,使得Nand Flash硬件上准备好数据,以供你之后读取,即对应着步骤⑤ */
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nand->nand_wait_ready(mtd);
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}
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/*还有一个步骤没有实现那就是步骤⑥了一点一点的把数据读出来*/
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nand_read_page_hwecc分析
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static int nand_read_page_hwecc(struct mtd_info *mtd, struct nand_chip *chip,
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uint8_t *buf, int oob_required, int page)
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{
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int i, eccsize = chip->ecc.size;
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int eccbytes = chip->ecc.bytes;
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int eccsteps = chip->ecc.steps;
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uint8_t *p = buf;
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uint8_t *ecc_calc = chip->buffers->ecccalc;
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uint8_t *ecc_code = chip->buffers->ecccode;
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uint32_t *eccpos = chip->ecc.layout->eccpos;
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unsigned int max_bitflips = 0;
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for (i = 0; eccsteps; eccsteps--, i += eccbytes, p += eccsize) {
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chip->ecc.hwctl(mtd, NAND_ECC_READ);
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chip->read_buf(mtd, p, eccsize);//这个函数必须有我们来实现
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chip->ecc.calculate(mtd, p, &ecc_calc[i]);
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}
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chip->read_buf(mtd, chip->oob_poi, mtd->oobsize);
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for (i = 0; i < chip->ecc.total; i++)
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ecc_code[i] = chip->oob_poi[eccpos[i]];
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eccsteps = chip->ecc.steps;
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p = buf;
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for (i = 0 ; eccsteps; eccsteps--, i += eccbytes, p += eccsize) {
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int stat;
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stat = chip->ecc.correct(mtd, p, &ecc_code[i], &ecc_calc[i]);
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if (stat < 0) {
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mtd->ecc_stats.failed++;
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} else {
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mtd->ecc_stats.corrected += stat;
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max_bitflips = max_t(unsigned int, max_bitflips, stat);
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}
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}
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return max_bitflips;
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}
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上面的 read_buf,就是真正的去读取数据的函数了,由于不同的Nand Flash controller 控制器所实现的方式不同,所以这个函数必须在你的 Nand Flash驱动中实现,即MTD 层,能帮我们实现的都实现了,不能实现的,那肯定是我们自己的事情了。。。
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