Re: [PATCH 2/4] mtd: nand: implement two pairing scheme

[Boris Brezillon <boris.brezillon@free-electrons.com>]

On Sun, 12 Jun 2016 14:42:15 +0200
Boris Brezillon <boris.brezillon@free-electrons.com> wrote:

> >   
> > >> Also, the data sheets are a real PITA to find.  I have yet to
> > >> see an actual data sheet that documents the stride-3 pairing scheme.    
> >   
> > > Yes, that's a real problem. Here is a Samsung NAND data sheet
> > > describing stride-3 [1], and an Hynix one describing stride-6 [2].
> > > 
> > > [1]http://dl.btc.pl/kamami_wa/k9gbg08u0a_ds.pdf
> > > [2]http://www.szyuda88.com/uploadfile/cfile/201061714220663.pdf    
> > 
> > Thank you very much!
> > 
> > Did you see the footnote at the bottom of p. 64 of the latter?
> > Does that affect your pair/group addressing scheme?
> > 
> > It seems they are grouping not just 8K pages into even/odd double-pages,
> > and those 16K double-pages are being addressed with stride of 3.
> > 
> > But in particular, an interrupted write is likely to corrupt both
> > double-pages, 32K of data!  
> 
> Yes, that's yet another problem I decided to ignore for now :).

Now I remember why I decided to ignore this. If you look at this other
Hynix data sheet [1] exposing the same pairing scheme you see that the
description as slightly changed. I don't know if it's a fix from the
previous description or if the pairing scheme are really different, but
until someone has tested it on a real device, I'll assume the Hynix
case is an exception which should be handled separately.

> 
> I guess a solution would be to consider that all 4 pages are 'paired'
> together, but this also implies considering that the NAND is a 4-level
> cells, which will make us loose even more space when operating in 'SLC
> mode' where we only write the lower page (page attached to group 0) of
> each pair.
> 

[1]http://minipcsale.ru/images/joomlakassa/TV_BOX/MINIX_NEO_X7/SK%20Hynix%20H27UCG8T2BTR.pdf

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com