Re: [EXT] [PATCH v2 3/3] mtd: rawnand: micron: Address the shallow erase issue

[Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>]

On Wed, 6 May 2020 22:59:39 +0200 (CEST)
Richard Weinberger <richard@xxxxxx> wrote:

> ----- Ursprüngliche Mail -----
> >> UBI scans only headers during attach. If you don't touch these, no way.  
> > 
> > Sorry, I misunderstood what you meant by payload. UBI should schedule
> > the PEB for erase if the EC/VID header is corrupted.  
> 
> UBI even tries to recover from such a situation. If only the EC header is bad,
> it will create a new one. Only of the VID header is bad/missing and the payload
> is corrupted (ECC errors or bit-flips) it will erase it.

Yep, I remember that, though in the case of a corrupted EC, UBI will
schedule a PEB recovery, and if the payload is corrupted, the read
should fail when copying the LEB content to another block.

> 
> A missing VID header plus good payload will cause UBI to stop attaching since it
> violates the IO model.

Sure, and that's not what we want to do anyway. We basically have 2
choices here:

1/ overwrite all pages starting from page 0 and ending at page 15. This
will lead to ECC errors on already written pages, and 0-filled pages
for others (unless we go for a raw write, in which case it might
actually lead to ECC errors depending on the engine).
2/ track already written pages (by reading them first), and only writes
those that have not been written yet. That means no ECC error in that
case, and no corrupted EC/VID header as well.

Clearly, #2 would help mitigate the perf penalty incurred by the Micron
workaround, but if it's not an option, maybe we can just start with
#1 (which is basically what Miquel implemented).

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