Re: imx27: No space left to write bad block table

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Stefan,

> > Interesting. Maybe I overlooked the below commit when applying. Indeed,
> > BBT may be considered as bad blocks, so I wonder if the below change is
> > valid now...
> > 
> > Guillaume, would you have a way to revert this patch on top of
> > linux-next? Stefan, would you mind giving more details on the testing
> > procedure?  
> 
> I have tested this on an i.MX 6 by simulating two bad BBT blocks by simply
> returning -EIO in nand_erase_nand when the block to be erased is one of the
> first two BBT blocks.
> 
> I have seen this once on a customer board but were not able to reproduce it
> anymore, thus the simulation of the two bad blocks.
> 
> Without the patch below new versions of the BBT can no longer be written to
> the first two blocks reserved for the BBT but they are still evaluated to read
> the BBT from during boot due the lack of a test if these blocks are bad. So
> changes to the BBT after these two blocks turn bad are only kept and used
> until the next reboot where again the old version of the two worn blocks is
> used as a basis.
> 
> I tried to use the same mechanism that is used to identify bad blocks during a
> scan for bad blocks. But maybe I missed something there? Or were my
> assumptions wrong in the first place?

Honestly I don't know what is wrong exactly in this patch.

We will revert the commit as it clearly breaks something fundamental
and the merge window is too close to adopt a hackish attitude.

I would propose the following tests with your board:
- Hack the core to allow yourself to access bad blocks from userspace
  for testing purposes.
- With the below commit, you should have the same behavior than
  reported by Fabio.
- Revert the commit.
- Manually change the bad block markers (nanddump, flash_erase,
  nandwrite) to declare the two tables bad. Reboot and observe if there
  are any issues. You can try to work from there.

> > ---8<---
> > 
> > commit bd9c9fe2ad04546940f4a9979d679e62cae6aa51
> > Author: Stefan Riedmueller <s.riedmueller@phytec.de>
> > Date:   Thu Mar 25 11:23:37 2021 +0100
> > 
> >     mtd: rawnand: bbt: Skip bad blocks when searching for the BBT in NAND
> >     
> >     The blocks containing the bad block table can become bad as well. So
> >     make sure to skip any blocks that are marked bad when searching for the
> >     bad block table.
> >     
> >     Otherwise in very rare cases where two BBT blocks wear out it might
> >     happen that an obsolete BBT is used instead of a newer available
> >     version.
> >     
> >     Signed-off-by: Stefan Riedmueller <s.riedmueller@phytec.de>
> >     Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> >     Link: 
> > https://lore.kernel.org/linux-mtd/20210325102337.481172-1-s.riedmueller@phytec.de
> > 
> > diff --git a/drivers/mtd/nand/raw/nand_bbt.c
> > b/drivers/mtd/nand/raw/nand_bbt.c
> > index dced32a126d9..6e25a5ce5ba9 100644
> > --- a/drivers/mtd/nand/raw/nand_bbt.c
> > +++ b/drivers/mtd/nand/raw/nand_bbt.c
> > @@ -525,6 +525,7 @@ static int search_bbt(struct nand_chip *this, uint8_t
> > *buf,
> >  {
> >         u64 targetsize = nanddev_target_size(&this->base);
> >         struct mtd_info *mtd = nand_to_mtd(this);
> > +       struct nand_bbt_descr *bd = this->badblock_pattern;
> >         int i, chips;
> >         int startblock, block, dir;
> >         int scanlen = mtd->writesize + mtd->oobsize;
> > @@ -560,6 +561,10 @@ static int search_bbt(struct nand_chip *this, uint8_t
> > *buf,
> >                         int actblock = startblock + dir * block;
> >                         loff_t offs = (loff_t)actblock << this-  
> > >bbt_erase_shift;  
> >  
> > +                       /* Check if block is marked bad */
> > +                       if (scan_block_fast(this, bd, offs, buf))
> > +                               continue;
> > +
> >                         /* Read first page */
> >                         scan_read(this, buf, offs, mtd->writesize, td);
> >                         if (!check_pattern(buf, scanlen, mtd->writesize,
> > td)) {
> > 
> > 
> > Thanks,
> > Miquèl  

Thanks,
Miquèl

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