questions about [PATCH]mtd: nand: fix SCAN2NDPAGE check for BBM

[Brian Norris]

On Tue, Oct 13, 2015 at 11:33:54AM +0000, Yanjiantao wrote:
> Dear Brian,
> 
> i read the patch:  " mtd: nand: fix SCAN2NDPAGE check for BBM "
> And i am confused about the markbad flows.
> 
> 		xxxxx;
>         if (chip->bbt_options & NAND_BBT_SCANLASTPAGE)
>                 ofs += mtd->erasesize - mtd->writesize;
> 
> 		xxxxx;
> 
>         do { 
>                 if (chip->options & NAND_BUSWIDTH_16) {
>                         chip->cmdfunc(mtd, NAND_CMD_READOOB,
>                                         chip->badblockpos & 0xFE, page);
>                         bad = cpu_to_le16(chip->read_word(mtd));
>                         if (chip->badblockpos & 0x1) 
>                                 bad >>= 8;
>                         else 
>                                 bad &= 0xFF;
>                 } else {
>                         chip->cmdfunc(mtd, NAND_CMD_READOOB, chip->badblockpos,
>                                         page);
>                         bad = chip->read_byte(mtd);
>                 }    
> 
>                 if (likely(chip->badblockbits == 8))
>                         res = bad != 0xFF;
>                 else 
>                         res = hweight8(bad) < chip->badblockbits;
>                 ofs += mtd->writesize;
>                 page = (int)(ofs >> chip->page_shift) & chip->pagemask;
>                 i++; 
>         } while (!res && i < 2 && (chip->bbt_options & NAND_BBT_SCAN2NDPAGE)); 
> mark bad flows is the same.
> 
> If I understand the patch right, then I think that:
> 1. when NAND_BBT_SCANLASTPAGE is set, markbad and checkbad on the last page only.
> 2. when NAND_BBT_SCAN2NDPAGE is set, markbad and checkbad on the 1st and 2nd page.
> 
> I checked some datasheets of different manufacturers(such as SAMSUNG/HYNIX/MICRON/TOSHIBA), they claim that bad block marker is on 1st/2nd, or 1st/last, or 1st/2nd/last(for spansion).
> the checkbad method may check fail in some cases:
> for example,:
> 1. for spansion nand(bad block marker is on 1st or 2nd or last page), set NAND_BBT_SCAN2NDPAGE while badblock marker is on last page or set NAND_BBT_SCANLASTPAGE while badblock marker is on 1st/2nd page may cause badblock chech failed.
> 2. for HYNIX (H27UBG8T2CTR) nand (bad block marker is on 1st or last page), check may failed whether NAND_BBT_SCANLASTPAGE is set or not.

Are you repeating the question from here [1]? The refer to my response
here [2].

Brian

[1] http://lists.infradead.org/pipermail/linux-mtd/2015-October/062486.html
[2] http://lists.infradead.org/pipermail/linux-mtd/2015-October/062509.html