Re: [PATCH v3] mtd: nand_bbt: scan for next free bbt block if writing bbt fails

[Kyle Roeschley]

Hi Boris,

On Wed, Mar 30, 2016 at 03:16:23PM +0200, Boris Brezillon wrote:
> +Peter, who's currently reworking the NAND BBT code.
> 
> On Wed, 30 Mar 2016 15:13:51 +0200
> Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx> wrote:
> 
> > Hi Kyle,
> > 
> > On Fri, 25 Mar 2016 17:31:16 -0500
> > Kyle Roeschley <kyle.roeschley@xxxxxx> wrote:
> > 
> > > If erasing or writing the BBT fails, we should mark the current BBT
> > > block as bad and use the BBT descriptor to scan for the next available
> > > unused block in the BBT. We should only return a failure if there isn't
> > > any space left.
> > > 
> > > Based on original code implemented by Jeff Westfahl
> > > <jeff.westfahl@xxxxxx>.
> > > 
> > > Signed-off-by: Kyle Roeschley <kyle.roeschley@xxxxxx>
> > > Suggested-by: Jeff Westfahl <jeff.westfahl@xxxxxx>
> > > ---
> > > This v3 is in response to comments from Brian Norris and Bean Ho on 8/26/15:
> > > http://lists.infradead.org/pipermail/linux-mtd/2015-August/061411.html
> > > 
> > > v3: Don't overload mtd->priv
> > >     Keep nand_erase_nand from erroring on protected BBT blocks
> > > 
> > > v2: Mark OOB area in each block as well as BBT
> > >     Avoid marking read-only, bad address, or known bad blocks as bad
> > > ---
> > >  drivers/mtd/nand/nand_base.c |  4 ++--
> > >  drivers/mtd/nand/nand_bbt.c  | 37 +++++++++++++++++++++++++++++++++++--
> > >  2 files changed, 37 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> > > index b6facac..9ad8a86 100644
> > > --- a/drivers/mtd/nand/nand_base.c
> > > +++ b/drivers/mtd/nand/nand_base.c
> > > @@ -2916,8 +2916,8 @@ int nand_erase_nand(struct mtd_info *mtd, struct erase_info *instr,
> > >  	/* Select the NAND device */
> > >  	chip->select_chip(mtd, chipnr);
> > >  
> > > -	/* Check, if it is write protected */
> > > -	if (nand_check_wp(mtd)) {
> > > +	/* Check if it is write protected, unless we're erasing BBT */
> > > +	if (nand_check_wp(mtd) && !allowbbt) {
> > 
> > Hm, will this really work. Can a write-protected device accept erase
> > commands?
> > 

Having looked into this more, no. Since v2, we called block_markbad in
write_bbt incorrectly and caused the chip to report that it was write
protected. Fixing that makes this unnecessary.

> > >  		pr_debug("%s: device is write protected!\n",
> > >  				__func__);
> > >  		instr->state = MTD_ERASE_FAILED;
> > > diff --git a/drivers/mtd/nand/nand_bbt.c b/drivers/mtd/nand/nand_bbt.c
> > > index 2fbb523..01526e5 100644
> > > --- a/drivers/mtd/nand/nand_bbt.c
> > > +++ b/drivers/mtd/nand/nand_bbt.c
> > > @@ -662,6 +662,7 @@ static int write_bbt(struct mtd_info *mtd, uint8_t *buf,
> > >  			page = td->pages[chip];
> > >  			goto write;
> > >  		}
> > > +	next:
> > 
> > Please put this label at the beginning of the line and fix all the other
> > issues reported by checkpatch (I know we already have a 'write' label
> > which does not follow this rule, but let's try to avoid adding new
> > ones).
> > 

Will do.

> > >  
> > >  		/*
> > >  		 * Automatic placement of the bad block table. Search direction
> > > @@ -787,14 +788,46 @@ static int write_bbt(struct mtd_info *mtd, uint8_t *buf,
> > >  		einfo.addr = to;
> > >  		einfo.len = 1 << this->bbt_erase_shift;
> > >  		res = nand_erase_nand(mtd, &einfo, 1);
> > > -		if (res < 0)
> > > +		if (res == -EIO) {
> > > +			/* This block is bad. Mark it as such and see if
> > > +			 * there's another block available in the BBT area. */
> > > +			int block = page >>
> > > +				(this->bbt_erase_shift - this->page_shift);
> > > +			pr_info("nand_bbt: failed to erase block %d when writing BBT\n",
> > > +				block);
> > > +			bbt_mark_entry(this, block, BBT_BLOCK_WORN);
> > > +
> > > +			res = this->block_markbad(mtd, block);
> > 
> > Not sure we should mark the block bad until we managed to write a new
> > BBT. ITOH, if we do so and the new BBT write is interrupted, it
> > will trigger a full BBM scan, which should be harmless on most
> > platforms (except those overwriting BBM with real data :-/)
> > 

So is your suggestion here just to swap the order of block_markbad and
bbt_mark_entry?

> > > +			if (res)
> > > +				pr_warn("nand_bbt: error %d while marking block %d bad\n",
> > > +					res, block);
> > > +			td->pages[chip] = -1;
> > > +			goto next;
> > > +		} else if (res < 0) {
> > >  			goto outerr;
> > > +		}
> > >  
> > >  		res = scan_write_bbt(mtd, to, len, buf,
> > >  				td->options & NAND_BBT_NO_OOB ? NULL :
> > >  				&buf[len]);
> > > -		if (res < 0)
> > > +		if (res == -EIO) {
> > > +			/* This block is bad. Mark it as such and see if
> > > +			 * there's another block available in the BBT area. */
> > > +			int block = page >>
> > > +				(this->bbt_erase_shift - this->page_shift);
> > > +			pr_info("nand_bbt: failed to write block %d when writing BBT\n",
> > > +				block);
> > > +			bbt_mark_entry(this, block, BBT_BLOCK_WORN);
> > > +
> > > +			res = this->block_markbad(mtd, block);
> > > +			if (res)
> > > +				pr_warn("nand_bbt: error %d while marking block %d bad\n",
> > > +					res, block);
> > > +			td->pages[chip] = -1;
> > > +			goto next;
> > > +		} else if (res < 0) {
> > >  			goto outerr;
> > > +		}
> > >  
> > >  		pr_info("Bad block table written to 0x%012llx, version 0x%02X\n",
> > >  			 (unsigned long long)to, td->version[chip]);
> > 
> > Bean, Brian, can you comment on this new version. I haven't followed
> > the previous iterations, and would like to have your feedback before
> > taking a decision.
> > 
> > Thanks,
> > 
> > Boris
> > 
> > 
> 
> 
> 
> -- 
> Boris Brezillon, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com

Thanks for the feedback,

-- 
Kyle Roeschley
Software Engineer
National Instruments