Re: [PATCH] mtd: rawnand: nand_bbt: Skip bad blocks when searching for the BBT in NAND

[Alexander Dahl]

Hei hei,

Am Dienstag, 6. Juli 2021, 18:13:08 CEST schrieb Miquel Raynal:
> Hi Stefan,
> 
> Stefan Riedmueller <s.riedmueller@xxxxxxxxx> wrote on Fri, 25 Jun 2021
> 
> 14:38:21 +0200:
> > 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.
> > 
> > This only applies to drivers which make use of a bad block marker in
> > flash.
> > Other drivers won't be able to identify bad BBT blocks and thus can't skip
> > these.
> > 
> > Signed-off-by: Stefan Riedmueller <s.riedmueller@xxxxxxxxx>
> 
> Besides the alignment of the helper parameters (nitpick) the patch
> looks good to me. If we can get someone to test it before the merge
> window closes it's perfect. Otherwise I'll apply it and we'll let robots
> do the job.

Added the patch on top of v5.10.21 and booted a SAMA5D27 based board, from the 
boot log:

nand: device found, Manufacturer ID: 0x01, Chip ID: 0xda
nand: AMD/Spansion S34ML02G1
nand: 256 MiB, SLC, erase size: 128 KiB, page size: 2048, OOB size: 64
Bad block table found at page 131008, version 0xFF
Bad block table found at page 130944, version 0xFF
6 cmdlinepart partitions found on MTD device atmel_nand
Creating 6 MTD partitions on "atmel_nand":
0x000000000000-0x000000040000 : "bootstrap"
0x000000040000-0x000000100000 : "uboot"
0x000000100000-0x000000140000 : "env1"
0x000000140000-0x000000180000 : "env2"
0x000000180000-0x000000200000 : "reserved"
0x000000200000-0x000010000000 : "UBI"
NET: Registered protocol family 17
ubi0: attaching mtd5
random: fast init done
ubi0: scanning is finished
ubi0: attached mtd5 (name "UBI", size 254 MiB)
ubi0: PEB size: 131072 bytes (128 KiB), LEB size: 126976 bytes
ubi0: min./max. I/O unit sizes: 2048/2048, sub-page size 2048
ubi0: VID header offset: 2048 (aligned 2048), data offset: 4096
ubi0: good PEBs: 2028, bad PEBs: 4, corrupted PEBs: 0
ubi0: user volume: 4, internal volumes: 1, max. volumes count: 128
ubi0: max/mean erase counter: 4/1, WL threshold: 4096, image sequence number: 
1600812189
ubi0: available PEBs: 0, total reserved PEBs: 2028, PEBs reserved for bad PEB 
handling: 36
ubi0: background thread "ubi_bgt0d" started, PID 85

No suspicious other messages. 

Not sure if that device would be affected anyways. No bad blocks are known on 
this flash, device behaves as usual.

HTH & Greets
Alex

> 
> > ---
> > 
> > Hi,
> > 
> > this is the second approach of this patch. The first one [1] unfortunately
> > lead to boot failures on i.MX 27 boards [2] since the i.MX 27 driver uses
> > the bad block marker position for the bad block table marker which lead
> > to falsely identifying all BBT blocks as bad.
> > 
> > This new patch now skips the check for bad BBT blocks if the BBT marker
> > position in OOB overlaps with the bad block marker position or if a driver
> > can't use bad block markers in flash at all (NAND_BBT_NO_OOB_BBM or
> > NAND_NO_BBM_QUIRK are set). This hopefully makes sure we don't break
> > drivers which cannot check for bad BBT blocks due to the limitations
> > mentioned before.
> > 
> > I was only able to test this patch on a phyCORE-i.MX 6 and a phyCARD-i.MX
> > 27. Therfore would really appreciate more people testing this to make
> > sure I have not missed another use case where the bad block marker
> > position in OOB is used in a different way than for the BBM.
> > 
> > Regards,
> > Stefan
> > 
> > [1]
> > https://lore.kernel.org/linux-mtd/20210325102337.481172-1-s.riedmueller@p
> > hytec.de/ [2]
> > https://lore.kernel.org/linux-mtd/CAOMZO5DufVR=+EzCa1-MPUc+ZefZVTXb5Kgu3W
> > xms7cxw9GmGg@xxxxxxxxxxxxxx/> 
> >  drivers/mtd/nand/raw/nand_bbt.c | 34 +++++++++++++++++++++++++++++++++
> >  1 file changed, 34 insertions(+)
> > 
> > diff --git a/drivers/mtd/nand/raw/nand_bbt.c
> > b/drivers/mtd/nand/raw/nand_bbt.c index dced32a126d9..2a30714350ee 100644
> > --- a/drivers/mtd/nand/raw/nand_bbt.c
> > +++ b/drivers/mtd/nand/raw/nand_bbt.c
> > @@ -447,6 +447,36 @@ static int scan_block_fast(struct nand_chip *this,
> > struct nand_bbt_descr *bd,> 
> >  	return 0;
> >  
> >  }
> > 
> > +/* Check if a potential BBT block is marked as bad */
> > +static int bbt_block_checkbad(struct nand_chip *this,
> > +				      struct nand_bbt_descr *td,
> > +				      loff_t offs, uint8_t *buf)
> > +{
> > +	struct nand_bbt_descr *bd = this->badblock_pattern;
> > +
> > +	/*
> > +	 * No need to check for a bad BBT block if the BBM area overlaps with
> > +	 * the bad block table marker area in OOB since writing a BBM here
> > +	 * invalidates the bad block table marker anyway.
> > +	 */
> > +	if (!(td->options & NAND_BBT_NO_OOB) &&
> > +	    td->offs >= bd->offs && td->offs < bd->offs + bd->len)
> > +		return 0;
> > +
> > +	/*
> > +	 * There is no point in checking for a bad block marker if writing
> > +	 * such marker is not supported
> > +	 */
> > +	if (this->bbt_options & NAND_BBT_NO_OOB_BBM ||
> > +	    this->options & NAND_NO_BBM_QUIRK)
> > +		return 0;
> > +
> > +	if (scan_block_fast(this, bd, offs, buf) > 0)
> > +		return 1;
> > +
> > +	return 0;
> > +}
> > +
> > 
> >  /**
> >  
> >   * create_bbt - [GENERIC] Create a bad block table by scanning the device
> >   * @this: NAND chip object
> > 
> > @@ -560,6 +590,10 @@ 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 (bbt_block_checkbad(this, td, offs, buf))
> > +				continue;
> > +
> > 
> >  			/* Read first page */
> >  			scan_read(this, buf, offs, mtd->writesize, td);
> >  			if (!check_pattern(buf, scanlen, mtd->writesize, td)) {
> 
> Thanks,
> Miquèl
> 
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