Re: [PATCH] mtd: spi-nor: winbond: add Zetta ZD25Q128C support

["Michael Walle" <mwalle@kernel.org>]

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Hi,

> > Zetta normally uses BAh as its vendor ID. But for the ZD25Q128C they
> > took the one from Winbond and messed up the size parameters in SFDP.
> > Most functions seem compatible with the W25Q128, we just have to fix up
> > the size.
> >
> > Link: http://www.zettadevice.com/upload/file/20150821/DS_Zetta_25Q128_RevA.pdf
> > Link: https://www.lcsc.com/datasheet/lcsc_datasheet_2312081757_Zetta-ZD25Q128CSIGT_C19626875.pdf
> > Signed-off-by: Michael Walle <mwalle@kernel.org>
> > ---
> [...]
> > diff --git a/drivers/mtd/spi-nor/winbond.c b/drivers/mtd/spi-nor/winbond.c
> > index e065e4fd42a3..9f7ce5763e71 100644
> > --- a/drivers/mtd/spi-nor/winbond.c
> > +++ b/drivers/mtd/spi-nor/winbond.c
> > @@ -17,6 +17,31 @@
> >  		   SPI_MEM_OP_NO_DUMMY,					\
> >  		   SPI_MEM_OP_DATA_OUT(1, buf, 0))
> >  
> > +static int
> > +w25q128_post_bfpt_fixups(struct spi_nor *nor,
> > +			 const struct sfdp_parameter_header *bfpt_header,
> > +			 const struct sfdp_bfpt *bfpt)
> > +{
> > +	/*
> > +	 * Zetta ZD25Q128C is a clone of the Winbond device. But the encoded
> > +	 * size is really wrong. It seems that they confused Mbit with MiB.
> > +	 * Thus the flash is discovered as a 2MiB device.
> > +	 */
> > +	if (bfpt_header->major == SFDP_JESD216_MAJOR &&
> > +	    bfpt_header->minor == SFDP_JESD216_MINOR &&
> > +	    nor->params->size == SZ_2M &&
> > +	    nor->params->erase_map.regions[0].size == SZ_2M) {
> > +		nor->params->size = SZ_16M;
> > +		nor->params->erase_map.regions[0].size = SZ_16M;
> > +	}
>
> Since the size is 16 MiB for both Zetta and Winbond, why do you have
> these conditions here? Why not just do it unconditionally? What
> situation do you want to protect against?

Two things, I want to make sure, the values I'll overwrite (which
were set indirectly by the SFDP data I check here) are really the
"before" value I expect them to be. And secondly, I want to
fingerprint the SFDP as accurately as possible. I mean you wouldn't
need the SFDP version either. Think of a preparation for a possible
.match() callback in zetta.c. That would probably look like this,
i.e. check the flash id and these four conditions.

What are your concerns?

-michael

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