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SubjectRe: [PATCH] Make the mtdblock read/write skip the bad nand sector
2013/11/21 Hans Zhang <zhanghonghui@innofidei.com>:
> When read/write the nandblock device, it will abort writing if
> there's a bad block, it's reasonable to skip the bad block and
> finish the data writing.
> The data reading procedure should also skip the bad block since
> there's no data write to the block.
>
> --v2:
> use the wrapped mtd_block_isbad instand of mtd->block_isbad
>
> Signed-off-by: Hans Zhang <zhanghonghui@innofidei.com>
> ---
> drivers/mtd/mtdblock.c | 17 +++++++++++++++++
> 1 files changed, 17 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/mtd/mtdblock.c b/drivers/mtd/mtdblock.c
> index 485ea75..4f6acd1 100644
> --- a/drivers/mtd/mtdblock.c
> +++ b/drivers/mtd/mtdblock.c
> @@ -124,6 +124,13 @@ static int write_cached_data (struct mtdblk_dev *mtdblk)
> "at 0x%lx, size 0x%x\n", mtd->name,
> mtdblk->cache_offset, mtdblk->cache_size);
>
> +retry:
> + ret = mtd_block_isbad(mtd, mtdblk->cache_offset);
> + if (ret > 0) {
> + mtdblk->cache_offset += mtdblk->cache_size;
> + goto retry;
> + }
> +
> ret = erase_write (mtd, mtdblk->cache_offset,
> mtdblk->cache_size, mtdblk->cache_data);
> if (ret)
> @@ -163,6 +170,11 @@ static int do_cached_write (struct mtdblk_dev *mtdblk, unsigned long pos,
> size = len;
>
> if (size == sect_size) {
> + ret = mtd_block_isbad(mtd, pos);
> + if (ret > 0) {
> + pos += sect_size;
> + continue;
> + }
> /*
> * We are covering a whole sector. Thus there is no
> * need to bother with the cache while it may still be
> @@ -242,6 +254,11 @@ static int do_cached_read (struct mtdblk_dev *mtdblk, unsigned long pos,
> mtdblk->cache_offset == sect_start) {
> memcpy (buf, mtdblk->cache_data + offset, size);
> } else {
> + ret = mtd_block_isbad(mtd, pos);
> + if (ret > 0) {
> + pos += sect_size;
> + continue;
> + }
> ret = mtd_read(mtd, pos, size, &retlen, buf);
> if (ret)
> return ret;
> --
> 1.7.1
>
>

I don't think it's a good idea to skip bad blocks at mtd level.
That will definitely break the userspace.
The nanddump mtd-tool for instance has a bad block handling argument:
--bb=METHOD, where METHOD can be `padbad', `dumpbad', or `skipbad':
padbad: dump flash data, substituting 0xFF for any bad blocks
dumpbad: dump flash data, including any bad blocks
skipbad: dump good data, completely skipping any bad blocks (default)

The bad block handling is done by the upper layer (UBI/jffs2...) not by mtd.

So, if you really need to read/write the mtd layer from userspace and
jump bad block, you'll have to use the MEMGETBADBLOCK ioctl to check
if the block is bad before reading/writing.

But using UBI is usually a better option.


Richard.


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