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

[Kyle Roeschley]

On Fri, Apr 29, 2016 at 09:16:31PM +0200, Boris Brezillon wrote:
> On Fri, 29 Apr 2016 12:34:18 -0500
> Kyle Roeschley <kyle.roeschley@xxxxxx> wrote:
> 
> > 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?
> 
> No, my suggestion was to move this->block_markbad() call after
> scan_write_bbt(), but this leads to another problem: if the BBT content
> is still valid after the erasure and you move this->block_markbad(),
> you might have a power-cut in the middle and the BBT detection code
> will pick the first valid one BBT (i.e. the one you were about to mark
> as bad).
> Again, this is all hypothetical, and anyway, the current BBT
> implementation is not so robust, so maybe we shouldn't care and rely on
> full bad block scan in this case (too bad for controllers that did not
> take care of keeping valid bad block markers :-/).

Sounds like a plan, I'll work on this.

-- 
Kyle Roeschley
Software Engineer
National Instruments