How to distinguish MLC and SLC NANDs?

[Juergen Beisert]

Hi Brian,

Brian Norris wrote:
> On Thu, Sep 15, 2011 at 7:33 AM, Juergen Beisert <jbe at pengutronix.de> wrote:
> > Is there a unique pattern for MLC
> > or SLC in the mtd structure available after calling nand_scan_ident() to
> > select what correction sum type should be used for the attached NAND?
>
> Actually, there isn't anything available in struct mtd_info. This
> belongs in struct nand_chip, actually, since it's a NAND-specific
> feature. In fact, there is some data available there. As you can see
> in nand_get_flash_type() in nand_base.c, we fill in the
> `chip->cellinfo' field, then later use a mask on it like this:
>
> chip->cellinfo & NAND_CI_CELLTYPE_MSK
>
> According to the data sheets for *most* NAND parts, this is a safe way
> of determining SLC vs. MLC (non-zero => MLC; zero => SLC), and we use
> it for certain detection code paths.

Hmm, *most* means this information is not reliable? Would it be better to give 
the driver a hint what kind of NAND it should expect via the platform_data?

> Note that if the chip uses ONFI, you supply your own ID table, or the chip
> uses some of the older ID codes, nand_base.c won't set chip->cellinfo for
> you; but it will default to SLC I think, which is the correct option for old
> parts. 

BTW: Is there a known disadvantage or incompatibility if I protect the data of 
an SLC with the more stronger ECC sums intended for MLCs (beside the effect 
the OOB area is more filled than required)?

> But it's up to you to determine your own reliance on this method. I
> don't know of any users who rely on `chip->cellinfo &
> NAND_CI_CELLTYPE_MSK' for this type of information.

I was in the hope of a perfect world and the MTD framework detects the NAND 
type reliable ;-). Now I tend more to use user's info from the platform_data.

Thanks for your answer.

Juergen

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