Re: [PATCH] mtd: spi-nor: Add support for MX25L12833F and MX25L12845G

[Miquel Raynal]

Hi Cheng Ming,

>> It looks like you're getting bitten by the ID reuse. You can't just
>> unconditionally add the quad PP because as far as I can see the
>> MX25L12805D [1] is just a standard single bit i/o flash and doesn't
>> support the 4PP.
>
> You are absolutely right. Thanks for catching this.
>
> The MX25L12805D is indeed a much older product (released around 2009).
> Since the initial JESD216 SFDP standard wasn't published until 2011,
> I double-checked with our internal PM and confirmed that the MX25L12805D
> does not support SFDP at all.
>
> Since the newer flashes (MX25L12833F and MX25L12845G) do support SFDP,
> we could use this as a differentiator to distinguish them from the legacy
> MX25L12805D.
>
> What if we try to read the SFDP signature (RDSFDP) in the fixup hook?
> If a valid SFDP signature is detected, we can safely identify it as the
> newer flash and apply the SNOR_HWCAPS_PP_1_4_4 capability. If there is
> no SFDP signature, we leave it as is for the legacy MX25L12805D.
>
> Do you think this approach is feasible and acceptable? If so, I will
> implement this logic and submit a v2 patch.

The ->post_sfdp() fixup hook is documented as "not called for SPI NORs
that do not support SFDP". Alternatively, I believe an earlier hook,
like ->post_bfpt() could also work since it does not seem to run on
non SFDP compatible flashes.

Thanks,
Miquèl