Re: [PATCH 3/3] mtd: mxc-nand: Only automatically create BBT if NAND seems to be pristine

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

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Hallo Sascha,

On Fri, May 03, 2024 at 09:44:24AM +0200, Sascha Hauer wrote:
> On Tue, Apr 30, 2024 at 11:44:54AM +0200, Uwe Kleine-König wrote:
> > Automatically creating a BBT is the right thing to do if the NAND is
> > factory new. However when migrating from a barebox older than commit
> > v2020.03.0~28^2~1 ("mtd: nand-imx: Create BBT automatically when
> > necessary") on a used machine, this automatism is really bad because it
> > most likely marks the blocks containing the barebox image (and possibly
> > more) as bad. On such a system the vendor BBMs are gone, but it was
> > operated without that information before, so continuing to do so is a
> > sane option.
> > 
> > Add a light check for the NAND to be really pristine: If the first block
> > looks like containing a barebox image or a UBI refuse to create a BBT.
> > 
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> > ---
> >  drivers/mtd/nand/raw/mxc_nand.c | 58 ++++++++++++++++++---------------
> >  1 file changed, 31 insertions(+), 27 deletions(-)
> > 
> > diff --git a/drivers/mtd/nand/raw/mxc_nand.c b/drivers/mtd/nand/raw/mxc_nand.c
> > index a72275480144..fd5ae447a198 100644
> > --- a/drivers/mtd/nand/raw/mxc_nand.c
> > +++ b/drivers/mtd/nand/raw/mxc_nand.c
> > @@ -1555,30 +1555,6 @@ static const struct nand_controller_ops mxcnd_controller_ops = {
> >   * From this point on we can forget about the BBMs and rely completely
> >   * on the flash BBT.
> >   */
> > -static int checkbad(struct nand_chip *chip, loff_t ofs)
> > -{
> > -	struct mtd_info *mtd = nand_to_mtd(chip);
> > -	int ret;
> > -	uint8_t buf[mtd->writesize + mtd->oobsize];
> > -	struct mtd_oob_ops ops;
> > -
> > -	ops.mode = MTD_OPS_RAW;
> > -	ops.ooboffs = 0;
> > -	ops.datbuf = buf;
> > -	ops.len = mtd->writesize;
> > -	ops.oobbuf = buf + mtd->writesize;
> > -	ops.ooblen = mtd->oobsize;
> > -
> > -	ret = mtd_read_oob(mtd, ofs, &ops);
> > -	if (ret < 0)
> > -		return ret;
> > -
> > -	if (buf[2000] != 0xff)
> > -		return 1;
> > -
> > -	return 0;
> > -}
> > -
> >  static int imxnd_create_bbt(struct nand_chip *chip)
> >  {
> >  	struct mtd_info *mtd = nand_to_mtd(chip);
> > @@ -1598,12 +1574,40 @@ static int imxnd_create_bbt(struct nand_chip *chip)
> >  
> >  	for (i = 0; i < numblocks; ++i) {
> >  		loff_t ofs = i << chip->bbt_erase_shift;
> > +		uint8_t buf[mtd->writesize + mtd->oobsize];
> > +		struct mtd_oob_ops ops = {
> > +			.mode = MTD_OPS_RAW,
> > +			.ooboffs = 0,
> > +			.datbuf = buf,
> > +			.len = mtd->writesize,
> > +			.oobbuf = buf + mtd->writesize,
> > +			.ooblen = mtd->oobsize,
> > +		};
> >  
> > -		ret = checkbad(chip, ofs);
> > -		if (ret < 0)
> > +		ret = mtd_read_oob(mtd, ofs, &ops);
> > +		if (ret < 0) {
> > +			dev_err(mtd->dev.parent, "Failed to read page at 0x%08x\n", (unsigned int)ofs);
> >  			goto out;
> > +		}
> >  
> > -		if (ret) {
> > +		/*
> > +		 * Automatically adding a BBT based on factory BBTs is only
> > +		 * sensible if the NAND is pristine. Abort if the first page
> > +		 * looks like a bootloader or UBI block.
> > +		 */
> > +		if (ofs == 0 && is_barebox_arm_head(buf)) {
> > +			dev_err(mtd->dev.parent, "Flash seems to contain a barebox image, refusing\n");
> > +			ret = -EINVAL;
> > +			goto out;
> > +		}
> > +
> > +		if (ofs == 0 && !memcmp(buf, "UBI#", 4)) {
> > +			dev_err(mtd->dev.parent, "Flash seems to contain a UBI, refusing\n");
> > +			ret = -EINVAL;
> > +			goto out;
> > +		}
> > +
> > +		if (buf[2000] != 0xff) {
> >  			bbt[i >> 2] |= 0x03 << (2 * (i & 0x3));
> >  			dev_info(mtd->dev.parent, "Bad eraseblock %d at 0x%08x\n",
> >  				 i, (unsigned int)ofs);
> 
> Could you add the new code to checkbad() instead of inlining it? That
> way it seems easier to adjust the code in case we have to change the way
> how we detect useful data on a page. Rename checkbad() in case the name
> doesn't feel appropriate anymore.

I hesitated to add the check for the chip being pristine to checkbad().
Then maybe read page 0 and check its contents before the check_bad()
loop? Then page 0 will be read twice but checkbad() can stay around and
only do what its name promises.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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