Re: [PATCH 13/15] mtd: nand: samsung: retrieve ECC requirements from extended ID

From: Valdis . Kletnieks
Date: Mon May 30 2016 - 16:58:11 EST

On Mon, 30 May 2016 09:44:46 +0200, Boris Brezillon said:
> Hi Valdis,

> Actually, that was my first reaction [1], but the more I think about it
> the more I realize it's a non-issue.
> AFAICT, there's no full-id entries for Samsung NANDs in the nand_ids
> table, so this either means there's no real users of Samsung MLCs or
> NAND controller drivers connecting to those chips don't care about the
> ->ecc_{step_ds,strength_ds} fields.

I'm mostly, though not totally convinced (not having looked closely at
the existing code). There's still a possible issue with the distinction

A) "driver never references the variable" and

B) driver check if it's zero, and acts like it doesn't care if it is, but if
it's non-zero, it goes ahead and uses it, with possible hilarity ensuing if the
value is wrong.

Should be pretty easy for somebody who knows the code better than I to rule
out case B fairly quickly...

> I agree that the solution is not perfect, but I'd prefer seeing the
> NAND detection code iteratively improved than rejecting everything
> until we're 100% sure that all cases are correctly handled (which might
> never happen since NAND vendors introduce new NAND ID scheme if they
> need to).
> BTW, do you have Samsung datasheets describing a different NAND ID
> format, or is it purely hypothetical?

Mostly hypothetical. I've just seen too many patches that assume "all chips
from vendor XYZ do *this*" that were not at all corrrect.

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