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

[Pratyush Yadav <pratyush@kernel.org>]

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.

>                 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@gmail.com/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/
>

-- 
Regards,
Pratyush Yadav