Re: [PATCH] mtd: spinand: Wait after erase in spinand_markbad

[Boris Brezillon <bbrezillon@xxxxxxxxxx>]

On Mon, 18 Feb 2019 12:27:25 +0100
Emil Lenngren <emil.lenngren@xxxxxxxxx> wrote:
  
> > > At the same time, it's generally disallowed to write the
> > > same page twice...  
> >
> > That's only if you care about the data you write to the page. Marking a
> > block bad is just about setting the BBM to 0x0, which should always work
> > even if the page you're writing to has already been written, simply
> > because a 1 -> 0 cell transition does not require an erase (only a 0 ->
> > 1 transition does).  
> 
> Should the BBM be written with or without ECC? Now it uses whatever
> mode was used in the last operation. Also for reading, I see the
> "spinand_isbad" function sets .mode to MTD_OPS_RAW but that field
> doesn't seem to be inspected, again using the same ECC mode as in the
> last operation.
> Isn't it best to use the non-ECC mode for both reading and writing the
> BBM?

We should definitely disable the ECC engine when reading/writing the
BBM.

> If we would use ECC mode and overwrite the page when writing the
> BBM marker, I guess the controller needs to store a second error
> correction code (overwriting the previous one), which will probably
> lead to ECC failure if later read in ECC-mode (and who knows if it
> will "correct" the zero bits to ones...).

Well, you could just ignore the ECC result, but that's better to simply
read the BBM in raw mode.

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