[PATCH v4 1/6] mtd: spi-nor: Add manufacturer read id function

[Michael Walle]

Am 2023-10-05 15:19, schrieb Tudor Ambarus:
> On 10/5/23 12:43, Michael Walle wrote:
>> Hi,
>> 
> hey
> 
>>>> I see this flash supports 1-1-1, 8-8-8, and 8d-8d-8d, there are no 
>>>> mixed
>>>> modes supported, thus a 8d-8d-8s mode seems just like a hardware bug 
>>>> to
>>>> me. So my proposal is to leave the core away and to handle the read 
>>>> id
>>>> hack just in the macronix driver.
>>> 
>>> +1
>> 
>> I've looked at the xspi spec. There is no RDID specified. So I'd 
>> argue,
>> the only pseudo standard is that RDID was only ever used with 1s1s1s. 
>> But
>> we added spi_nor_read_id() with parameters suited for the "unusual" 
>> 8d8d8d
>> case with additional address and dummy cycles. Just for checking 
>> whether
>> the
>> octal-dtr switch was successful. Therefore, we've already added
>> parameters to
>> spi_nor_read_id() which are not standard. Then we can just add one 
>> more.
>> It's
>> just how macronix is doing it. Again there is no standard.
>> If we'd only put standard (or for the 9F pseudo standard) things in 
>> the
>> core,
>> then spi_nor_read_id() would need to check whether the flash is in 
>> 1s1s1s
>> mode. And no I wouldn't prefer that ;)
>> 
> 
> If we really want to be catholic, we should switch to 8d-8d-8s mode and
> then issue the read id and the core will handle the readid correctly.
> But there is no such a thing, because macronix considers that it is in
> 8d-8d-8d mode at the time of issuing 8d-8d-8s read id. That's why I say
> it's a bug on their side. The core is meant to be generic, I don't want
> to pollute the core with manufacturer specific fixes.

Then why does spi_nor_read_id() have the following parameters:

  * @naddr:      number of address bytes to send. Can be zero if the 
operation
  *              does not need to send an address.
  * @ndummy:     number of dummy bytes to send after an opcode or 
address. Can
  *              be zero if the operation does not require dummy bytes.
  * @proto:      the SPI protocol for register operation.

They aren't standard either. It's just the way spansion and micron 
transfers
the ID via RDID in octal DTR mode. And now there's macronix who does it 
slightly
different. But *neither* of them are standard. Why should one be in the 
core and
one shouldn't.

spi_nor_read_id() should just handle proto == SNOR_PROTO_8D_8D_8S.

-michael