[PATCH 1/2] nand_base: SOFT_BCH: Request strength over bytes

[Aaron Sierra]

----- Original Message -----
> From: "Boris Brezillon" <boris.brezillon at free-electrons.com>
> Sent: Wednesday, January 14, 2015 3:34:49 AM
> 
> Hi Aaron,
> 
> On Mon, 12 Jan 2015 18:35:55 -0600 (CST)
> Aaron Sierra <asierra at xes-inc.com> wrote:
> 
> > Previously, we requested that drivers pass ecc.size and ecc.bytes when
> > using NAND_ECC_SOFT_BCH. However, a driver is likely to only know the ECC
> > strength required for its NAND, so each driver would need to perform a
> > strength-to-bytes calculation.
> > 
> > Avoid duplicating this calculation in each driver by asking drivers to
> > pass ecc.size and ecc.strength so that the strength-to-bytes calculation
> > need only be implemented once.
> > 
> > This reverts/generalizes this commit:
> >     mtd: nand: Base BCH ECC bytes on required strength
> 
> Apart from the nit below, you can add my:
> 
> Reviewed-by: Boris Brezillon <boris.brezillon at free-electrons.com>
> 
> > 
> > Signed-off-by: Aaron Sierra <asierra at xes-inc.com>
> > ---
> >  drivers/mtd/nand/nand_base.c  | 21 +++++++++++++++------
> >  drivers/mtd/nand/sunxi_nand.c |  2 --
> >  2 files changed, 15 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> > index 41585df..993612c 100644
> > --- a/drivers/mtd/nand/nand_base.c
> > +++ b/drivers/mtd/nand/nand_base.c
> > @@ -4028,22 +4028,31 @@ int nand_scan_tail(struct mtd_info *mtd)
> >  		ecc->read_oob = nand_read_oob_std;
> >  		ecc->write_oob = nand_write_oob_std;
> >  		/*
> > -		 * Board driver should supply ecc.size and ecc.bytes values to
> > -		 * select how many bits are correctable; see nand_bch_init()
> > -		 * for details. Otherwise, default to 4 bits for large page
> > -		 * devices.
> > +		 * Board driver should supply ecc.size and ecc.strength values
> > +		 * to select how many bits are correctable. Otherwise, default
> > +		 * to 4 bits for large page devices.
> >  		 */
> >  		if (!ecc->size && (mtd->oobsize >= 64)) {
> >  			ecc->size = 512;
> > -			ecc->bytes = DIV_ROUND_UP(13 * ecc->strength, 8);
> > +			ecc->strength = 4;
> >  		}
> > +
> > +		/*
> > +		 * We previously recommended drivers pass ecc.size and
> > +		 * ecc.bytes. Continue to support drivers that do.
> > +		 * See nand_bch_init() for details.
> > +		 */
> > +		if (ecc->bytes && !ecc->strength)
> > +			ecc->strength = ecc->bytes * 8 / fls(8 * ecc->size);
> 
> How about fixing all NAND_ECC_SOFT_BCH users (AFAICT the only remaining
> one is nandsim, since you fixed sunxi_nand) instead of keeping this
> backward compat code.

Boris,
Yes, nandsim was the only other that I found. I will submit an update that
does not include this backward compatibility code, thanks.

-Aaron

> 
> Best Regards,
> 
> Boris