Re: [PATCH] mtd: spinand: winbond: Add support for W25N08LW

[Nuno Sá]

On Thu, Sep 03, 2026 at 12:12:15PM +0200, Miquel Raynal wrote:
> On 31/08/2026 at 16:38:10 +01, Nuno Sá <nuno.sa@xxxxxxxxxx> wrote:
> 
> > Add support for the W25N08LW, a 1.8V 8Gbit SPI-NAND made of two
> > 4Gbit LUNs, with 4096-byte pages and 256 bytes of spare area.
> >
> > The chip reuses the KV ECC status helper, but needs its own OOB
> > layout because the geometry of its spare area differs from the
> > existing Winbond parts. Only half of it is visible while the
> > internal ECC is enabled, so the ECC region is reported as
> > inaccessible and just the free bytes are exposed.
> >
> > Assisted-by: Claude:Opus-5
> > Signed-off-by: Nuno Sá <nuno.sa@xxxxxxxxxx>
> > ---
> >  drivers/mtd/nand/spi/winbond.c | 45 ++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 45 insertions(+)
> >
> > diff --git a/drivers/mtd/nand/spi/winbond.c b/drivers/mtd/nand/spi/winbond.c
> > index 9b78c1e6cbc9..c2c4cc306f05 100644
> > --- a/drivers/mtd/nand/spi/winbond.c
> > +++ b/drivers/mtd/nand/spi/winbond.c
> > @@ -345,6 +345,41 @@ static const struct mtd_ooblayout_ops w25n02kv_ooblayout = {
> >  	.free = w25n02kv_ooblayout_free,
> >  };
> >  
> > +static int w25n08lw_ooblayout_ecc(struct mtd_info *mtd, int section,
> > +				  struct mtd_oob_region *region)
> > +{
> > +	/*
> > +	 * With ecc enabled the parity bits are not accessible. So we can
> > +	 * only see page + 128. Without ecc the full page + 256 is accessible.
> > +	 * To make it simple just return the area as not accessible.
> > +	 */
> > +	return -ERANGE;
> > +}
> > +
> > +static int w25n08lw_ooblayout_free(struct mtd_info *mtd, int section,
> > +				   struct mtd_oob_region *region)
> > +{
> > +	if (section > 7)
> > +		return -ERANGE;
> > +
> > +	region->offset = (16 * section);
> > +	/* Note that we include User Data 2 which is not protected by ECC */
> 
> The more I think about these free bytes, the more I get convinced that
> we should only expose ECC protected bytes. I honestly do not remember
> any guarantee regarding these officially stated, the common case
> (eg. UBI) there is no impact, but maybe it is best to only expose the
> bytes that are actually protected, since the thresholds are getting
> lower and lower (and chances to get bitflips there increase with the
> optimizations of the technology).
> 
> Do you mind only exposing User Data 1?

Not at all! Will re-spin with that in mind!

Thx!
- Nuno Sá

> 
> Thanks,
> Miquèl
> 
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