Re: [PATCH v2 1/2] mtd: spi-nor: sst: Fix write enable before AAI sequence

[Hendrik Donner]

Hello,

On 3/13/26 12:46, Pratyush Yadav wrote:
> On Fri, Mar 06 2026, Hendrik Donner wrote:
>
> > Hello,
> >
> > On 2/23/26 10:29, Michael Walle wrote:
> > > Hi,
> > > On Mon Feb 23, 2026 at 10:17 AM CET, Sanjaikumar V S wrote:
> > > > > Raises concern about writes ending at odd offsets potentially
> > > > > having the same issue
> > > >
> > > > The odd end address case (trailing byte) is already handled in the
> > > > existing code at lines 243-255:
> > > >
> > > > /* Write out trailing byte if it exists. */
> > > > if (actual != len) {
> > > >       ret = spi_nor_write_enable(nor);
> > > >       ...
> > > >       ret = sst_nor_write_data(nor, to, 1, buf + actual);
> > > > }
> > > Ah, I must be blind. I stopped reading at the write_disable.
> > >
> > > > So write_enable is already called before writing the trailing
> > > > byte. My patch only addresses the odd start case where BP clears
> > > > WEL before the AAI sequence begins.
> > > >
> > > > > Suggests simplifying the conditional logic by removing the length
> > > > > check
> > > >
> > > > The condition `if (actual < len - 1)` avoids an unnecessary
> > > > write_enable when len == 1 (single byte write at odd address, no
> > > > AAI follows). But if you prefer unconditional write_enable for
> > > > simplicity, I can change it in v3.
> > > I know, but I actually don't like repeating the condition in the for
> > > loop. So I'd prefer to have a local "needs_write_enable" boolean
> > > which will be set to true. But then, I wouldn't care too much if
> > > there is a write enable followed by a write disable for a rare case.
> > >
> > > > > Notes the patch lacks runtime testing
> > > >
> > > > I don't have the hardware setup to test odd-address writes at the
> > > > moment. The fix is based on code analysis. I have tested patch 2/2
> > > > (dirmap fallback) on hardware.
> > > I'm hesitant - because like I said, if there is really a bug - it
> > > would have never worked correctly, since day 1. But yeah, I've also
> > > read the datasheet and it clearly states that the byte write will
> > > clear the write enable latch.
> >
> > i can confirm both patches fix real issues, i have similiar fixes
> > on a kernel tree i always wanted to clean up and upstream. Diffs
> > based on 6.6.127:
> >
> > diff --git a/drivers/mtd/spi-nor/sst.c b/drivers/mtd/spi-nor/sst.c
> > index 197d2c1101ed5..eaa50561ede2c 100644
> > --- a/drivers/mtd/spi-nor/sst.c
> > +++ b/drivers/mtd/spi-nor/sst.c
> > @@ -155,6 +155,13 @@ static int sst_nor_write(struct mtd_info *mtd, loff_t to, size_t len,
> >                  if (ret)
> >                          goto out;
> >
> > +               ret = spi_nor_write_enable(nor);
> > +               if (ret)
> > +                       goto out;
> > +               ret = spi_nor_wait_till_ready(nor);
> > +               if (ret)
> > +                       goto out;
> > +
> >                  to++;
> >                  actual++;
> >          }
> >
> >
> > diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
> > index 1b0c6770c14e4..646bfb2e91a65 100644
> > --- a/drivers/mtd/spi-nor/core.c
> > +++ b/drivers/mtd/spi-nor/core.c
> > @@ -276,7 +276,7 @@ static ssize_t spi_nor_spimem_write_data(struct spi_nor *nor, loff_t to,
> >          if (spi_nor_spimem_bounce(nor, &op))
> >                  memcpy(nor->bouncebuf, buf, op.data.nbytes);
> >
> > -       if (nor->dirmap.wdesc) {
> > +       if (nor->dirmap.wdesc && nor->program_opcode != SPINOR_OP_AAI_WP) {
>
> Why is this better? This removes the use of dirmap for all flashes other
> than SST.

i claim the opposite down below? That patch 2 of the posted patch series
looks better to me. Sorry if that was unclear.

Regards,
Hendrik

> >                  nbytes = spi_mem_dirmap_write(nor->dirmap.wdesc, op.addr.val,
> >                                                op.data.nbytes, op.data.buf.out);
> >          } else {
> >
> >
> > I think patch 2 of this series is the better approach though.
>
> There is a v4 here:
> https://lore.kernel.org/linux-mtd/20260311103057.29-1-sanjaikumarvs@xxxxxxxxx/T/#u
>
> Can you please review and test it so we can apply it?
>
> > Regards,
> > Hendrik
> >
> > > > Please let me know if you'd like me to send a v3 with the
> > > > simplified unconditional write_enable.
> > > Please see above.
> > > -michael
> > > ______________________________________________________
> > > Linux MTD discussion mailing list
> > > http://lists.infradead.org/mailman/listinfo/linux-mtd/