RE: [EXT] Re: [PATCH 6/8] mtd: spinand: micron: Turn driver implementation generic

["Shivamurthy Shastri (sshivamurthy)" <sshivamurthy@micron.com>]

Hi Boris,

Thank you for the review.

> 
> On Mon, 19 Aug 2019 09:03:38 +0000
> "Shivamurthy Shastri (sshivamurthy)" <sshivamurthy@micron.com> wrote:
> 
> > >
> > > >  static int micron_spinand_detect(struct spinand_device *spinand)
> > > >  {
> > > > +	const struct spi_mem_op *op;
> > > >  	u8 *id = spinand->id.data;
> > > > -	int ret;
> > > >
> > > >  	/*
> > > >  	 * Micron SPI NAND read ID need a dummy byte,
> > > > @@ -114,16 +102,55 @@ static int micron_spinand_detect(struct
> > > spinand_device *spinand)
> > > >  	if (id[1] != SPINAND_MFR_MICRON)
> > > >  		return 0;
> > > >
> > > > -	ret = spinand_match_and_init(spinand, micron_spinand_table,
> > > > -				     ARRAY_SIZE(micron_spinand_table),
> > > id[2]);
> > >
> > > I am not sure this is the right solution. I would keep this call and
> > > overwrite what you need to overwrite with the fixup hook.
> > >
> 
> I'm definitely not comfortable with this whole "rely on ONFi
> param-page" thing. Vendors have proven to get it wrong from time to
> time, so before we do that, I'd like to make sure all currently
> supported Micron NANDs (looks like we only support MT29F2G01ABAGD, so
> that shouldn't be hard) expose the right thing there. For instance, are
> we sure the ECC layout is always the same, and if not, do we have a
> reliable way to extract that?
> 
> >
> > Then, I will have dummy structure like below.
> >
> > static const struct spinand_info micron_spinand_table[] = {
> >         SPINAND_INFO(NULL, 0,
> >                      NAND_MEMORG(0, 0, 0, 0, 0, 0, 0, 0, 0),
> >                      NAND_ECCREQ(0, 0),
> >                      SPINAND_INFO_OP_VARIANTS(&read_cache_variants,
> >                                               &write_cache_variants,
> >                                               &update_cache_variants),
> >                      0,
> >                      SPINAND_ECCINFO(&micron_ooblayout_ops,
> >                                      micron_ecc_get_status)),
> > };
> 
> >
> > Let me know if you are thinking for different approach.
> 
> Exposing dummy entries is useless. If you're entirely sure all Micron
> SPI NANDs have a valid ONFi param page, then no need to use the
> ID-based detection. But as I said above, I feel param-page-based
> detection is going to be as messy as SFDP-based detection is for SPI
> NORs. Vendors tend to make mistakes which we have to fix to make
> things work. ID-based detection is much more reliable in this regard,
> as long as we don't have ID collisions :P.
> Plus, it looks like only a few manufacturers decided to use ONFi param
> pages to expose SPI NAND info (AFAICT, only Micron and Macronix do
> that), which is not surprising since the ONFi param page has been
> created to describe parallel NANDs not SPI NANDs (if you look closely
> enough, you'll notice that some fields are meaningless for SPI NANDs).

Okay, I will send new patches with ID-based detection for the new devices.


Thanks,
Shiva