Re: [RFC 2/3] mtd: spi-nor: core: compare JEDEC bytes to already found flash_info

[<Tudor.Ambarus@microchip.com>]

On 7/2/21 4:17 PM, Rasmus Villemoes wrote:
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> 
> On 23/06/2021 08.46, Tudor.Ambarus@microchip.com wrote:
>> Hi,
>>
>> On 6/22/21 11:58 PM, Rasmus Villemoes wrote:
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>>>
>>> On 22/06/2021 13.57, Michael Walle wrote:
>>>> [+ some people from MXIC as they are ones who posted to the ML
>>>> lately. Feel free to forward this mail to the corresponding people.]
>>>>
>>>> Am 2021-06-21 17:23, schrieb Rasmus Villemoes:
>>>>> Macronix engineers, in their infinite wisdom, have a habit of reusing
>>>>> JEDEC ids for different chips. There's already one
>>>>> workaround (MX25L25635F v MX25L25635E), but the same problem exists
>>>>> for MX25L3205D v MX25L3233F, the latter of which is not currently
>>>>> supported by linux.
>>>>>
>>>>> AFAICT, that case cannot really be handled with any of the ->fixup
>>>>> machinery: The correct entry for the MX25L3233F would read
>>>>>
>>>>>         { "mx25l3233f",  INFO(0xc22016, 0, 64 * 1024,  64, SECT_4K |
>>>>> SPI_NOR_DUAL_READ | SPI_NOR_QUAD_READ ) },
>>>>>
>>>>> while the existing one is
>>>>>
>>>>>     { "mx25l3205d",  INFO(0xc22016, 0, 64 * 1024,  64, SECT_4K) },
>>>>>
>>>>> So in spi_nor_init_params(), we won't even try reading the sfdp
>>>>> info (i.e. call spi_nor_sfdp_init_params), and hence
>>>>> spi_nor_post_sfdp_fixups() has no way of distinguishing the
>>>>> chips.
>>>>>
>>>>> Replacing the existing entry with the mx25l3233f one to coerce the
>>>>> core into issuing the SPINOR_OP_RDSFDP is also not really an option,
>>>>> because the data sheet for the mx25l3205d explicitly says not to issue
>>>>> any commands not listed ("It is not recommended to adopt any other
>>>>> code not in the command definition table, which will potentially enter
>>>>> the hidden mode.", whatever that means).
>>>>
>>>> Maybe we should ask Macronix if it is safe to send the RDSFDP command.
>>>> Can anyone from MXIC comment this?
>>>
>>> Yeah, that would be useful to know, but I don't have any hopes
>>> whatsoever of Macronix engineers being able to help sort out the mess
>>> they've created by reusing IDs in the first place. They don't seem to
>>> understand how that can possibly be a problem.
>>>
>>> I, and my client, have contacted them on several occasions to ask how
>>> we're supposed to deal with that. At one point, the answer was
>>> "MX25L3233F support Serial Flash Discoverable Parameters (SFDP) mode,
>>> MX25L3205D does not support.", but when I asked the obvious follow-up
>>> ("but the MX25L3205D datasheet warns against doing RDSFDP or any other
>>> not explicitly allowed command"), I got no response.
>>>
>>> Another response was
>>>
>>> "I can only comment on Linux 4.4, as that is the only version that I
>>> have supporting material for. Basically we have a patch for MTD/SPI-NOR
>>> (see attached). This is to allow allow the MTD subsystem to cope with
>>> devices that have the same ID (see below first paragraph of application
>>> note attached). Please note that the MX25L3205D had an EOL notification
>>> on 14th May 2010."
>>>
>>> and that attached patch is a 173KB .patch file that made me taste my
>>> breakfast again.
>>>
>>> And they keep repeating the argument that when a chip is EOL, it's OK to
>>> reuse its ID (because obviously nobody have used that chip in a product
>>> that would receive OS updates, so any OS released later than that EOL
>>> date can just include support for the newer chip and drop the old one...).
>>>
>>>>> In order to support such cases, extend the logic in spi_nor_read_id()
>>>>> a little so that if we already have a struct flash_info* from the name
>>>>> in device tree, check the JEDEC bytes against that, and if it is a
>>>>> match, accept that (device tree compatible + matching JEDEC bytes) is
>>>>> stronger than merely matching JEDEC bytes.
>>>>
>>>> This won't help much without a proper dt schema. No in-tree devicetree
>>>> could use is because the DT validation would complain.
>>>
>>> I can certainly extend the regexp in jedec,spi-nor.yaml to match this
>>> new one. DT is supposed to describe the hardware, so I can't see how
>>> that could possibly be controversial.
>>
>> No, please don't go that path yet.
>>
>>>
>>>  So if this will
>>>> go in (and the maintainers are rather hesitant to add it, I tried
>>>> it myself [1]), you'd also need to add it to jedec,spi-nor.yaml and
>>>> get an ack from Rob.
>>
>> I'm not hesitant, I'm keeping my NACK until we're sure there isn't any other way
>> to differentiate at run-time.
> 
> It seems that we have established that by now, right?
> 

It is unlikely that RDSFDP will cause any problems for the old MX25L3205D,
I would like to differentiate between the two flashes by parsing SFDP.

I'm preparing a patch set to address the all the ID collision thingy.
https://github.com/ambarus/linux-0day/commit/b760260efecb4f3678de3b78250f99338ecbad1b