Re: [PATCH v2 1/3] UBI: Do not zero out EC and VID on ECC-ed NOR flashes

[Pratyush Yadav <p.yadav@ti.com>]

On 28/11/20 10:58AM, Tudor.Ambarus@microchip.com wrote:
> On 11/18/20 8:24 PM, Pratyush Yadav wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> > 
> > For NOR flashes EC and VID are zeroed out before an erase is issued to
> > make sure UBI does not mistakenly treat the PEB as used and associate it
> > with an LEB.
> > 
> > But on some flashes, like the Cypress Semper S28 SPI NOR flash family,
> > multi-pass page programming is not allowed on the default ECC scheme.
> > This means zeroing out these magic numbers will result in the flash
> > throwing a page programming error.
> > 
> > Do not zero out EC and VID for such flashes. A writesize > 1 is an
> > indication of an ECC-ed flash.
> > 
> > Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
> > ---
> > 
> > Notes:
> >     Changes in v2:
> > 
> >     - Use mtd->writesize to check if multi-pass programming can be done
> >       instead of using MTD_NO_MULTI_PASS_WRITE.
> >     - Remove the assertion that a NOR flash most have writesize of 1.
> > 
> >  drivers/mtd/ubi/build.c | 4 +---
> >  drivers/mtd/ubi/io.c    | 9 ++++++++-
> >  2 files changed, 9 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
> > index e85b04e9716b..25fd7816b1f4 100644
> > --- a/drivers/mtd/ubi/build.c
> > +++ b/drivers/mtd/ubi/build.c
> > @@ -628,10 +628,8 @@ static int io_init(struct ubi_device *ubi, int max_beb_per1024)
> >                 ubi->bad_peb_limit = get_bad_peb_limit(ubi, max_beb_per1024);
> >         }
> > 
> > -       if (ubi->mtd->type == MTD_NORFLASH) {
> > -               ubi_assert(ubi->mtd->writesize == 1);
> > +       if (ubi->mtd->type == MTD_NORFLASH)
> >                 ubi->nor_flash = 1;
> > -       }
> > 
> >         ubi->min_io_size = ubi->mtd->writesize;
> >         ubi->hdrs_min_io_size = ubi->mtd->writesize >> ubi->mtd->subpage_sft;
> > diff --git a/drivers/mtd/ubi/io.c b/drivers/mtd/ubi/io.c
> > index 14d890b00d2c..2f3312c31e51 100644
> > --- a/drivers/mtd/ubi/io.c
> > +++ b/drivers/mtd/ubi/io.c
> > @@ -535,7 +535,14 @@ int ubi_io_sync_erase(struct ubi_device *ubi, int pnum, int torture)
> >                 return -EROFS;
> >         }
> > 
> > -       if (ubi->nor_flash) {
> > +       /*
> > +        * If the flash is ECC-ed then we have to erase the ECC block before we
> > +        * can write to it. But the write is in preparation to an erase in the
> > +        * first place. This means we cannot zero out EC and VID before the
> > +        * erase and we just have to hope the flash starts erasing from the
> > +        * start of the page.
> > +        */
> > +       if (ubi->nor_flash && ubi->mtd->writesize == 1) {
> 
> Are there any SPI NORs with ECC block size of 4 bytes? Should we call
> nor_erase_prepare() in this case?

None that I know of. But even if there was such a flash this check would 
continue to be correct.

Like Vignesh explained in the previous version, mtd->writesize > 1 means 
that multi-pass writes are not allowed in that ECC block. So even if a 
flash has ECC block size of 4, we still are not allowed to write 4 (or 
less) bytes to it before erasing first.
 
> Anyway, there's none in SPI NOR as of now, so:
> 
> Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
> 
> >                 err = nor_erase_prepare(ubi, pnum);
> >                 if (err)
> >                         return err;
> > --
> > 2.28.0
> > 
> 

-- 
Regards,
Pratyush Yadav
Texas Instruments India