Re: [PATCH] mtd: spi-nor: Add support for w25qNNjwim

[Michael Walle]

Hi Tudor,

Am 2020-01-13 11:07, schrieb Michael Walle:
> > > Btw. is renaming the flashes also considered a backwards incomaptible
> > > change?
> >
> > No, we can fix the names.
> >
> > > And can there be two flashes with the same name? Because IMHO it 
> > > would
> > > be
> >
> > I would prefer that we don't. Why would you have two different 
> > jedec-ids with
> > the same name?
>
> Because as pointed out in the Winbond example you cannot distiguish 
> between
> W25Q32DW and W25Q32JWIQ; and in the Macronix example between MX25L8005 
> and
> MX25L8006E. Thus my reasoning was to show only the common part, ie 
> W25Q32
> or MX25L80 which should be the same for this particular ID. Like I 
> said, I'd
> prefer showing an ambiguous name instead of a wrong one. But then you 
> may
> have different IDs with the same ambiguous name.


Another solution would be to have the device tree provide a hint for the
actual flash chip. There would be multiple entries in the spi_nor_ids 
with the
same flash id. By default the first one is used (keeping the current
behaviour). If there is for example

  compatible = "jedec,spi-nor", "w25q32jwq";

the flash_info for the w25q32jwq will be chosen.

I know this will conflict with the new rule that there should only be

  compatible = "jedec,spi-nor";

without the actual flash chip. But it seems that it is not always 
possible
to just use the jedec id to match the correct chip.

Also see for example mx25l25635_post_bfpt_fixups() which tries to figure
out different behaviour by looking at "some" SFDP data. In this case we
might have been lucky, but I fear that this won't work in all cases and
for older flashes it won't work at all.

BTW I do not suggest to add the strings to the the spi_nor_dev_ids[].

I guess that would be a less invasive way to fix different flashes with
same jedec ids.

-michael