[Yaffs] cvs YAFFS + MTD cvs + 2.4.27-vrs1 problems

[Charles Manning]

On Friday 10 December 2004 21:47, Thomas Gleixner wrote:
> On Fri, 2004-12-10 at 13:32 +1300, Charles Manning wrote:
> > I might argue the latter point here. I believe the ECC byte ordering
> > calculated by SJHill's nand_ecc.c is wrong.   yaffs_ecc.c can calcula=
te
> > this ECC order or the SmartMedia "correct" order.  yaffs_ecc.c is als=
o
> > slightly faster than nand_ecc.c ;-).
>
> I have no problem to put a faster algorithm into nand_ecc.c. The byte
> ordering is simple to fix by
>
> -        eccpos: {8, 9, 10, 13, 14, 15}
> +        eccpos: {9, 8, 10, 14, 13, 15}
>
> or whatever byte ordering is the correct one.
>
> > I don't think I have a gripe with the ECC stuff, it's the write
> > verification that gets me.
>
> Why ? The nand driver provides write verify and tells you when it
> failed.

When I write the deletion markers or bad block marking  I don't want to u=
se=20
verification.=20

When you program NAND, writing 0xFF does not mean "set this to 0xFF" it m=
eans=20
"don't do anything to these bytes". The verifying does not work this way.=
=20
Perhaps it would be nice to have a flag to apply or ignore verification.

>
> > From my understanding this is only a configuration issue.
> >
> > YAFFS can be build with CONFIG_YAFFS_USE_NAND_ECC which means yaffs w=
on't
> > do ECC - it lets mtd do all ECC. This is, IMHO, the best way to do th=
ings
> > with Linux - particularly if there are other non-yaffs users of the N=
AND.
> >
> > With non-Linux usage, I recommend using yaffs_ecc.c if software ECC i=
s
> > required.
>
> Sure, but I strongly recommend to seperate this from the filesystem.

In YAFFS2 it is so :-).

>
> > Where things do break down a bit is with mkyaffs which does calculate
> > ECC. You need to be careful to use a consistent ECC strategy.
>
> Yep, but I notice that most newer designs use hardware ecc, which
> sometimes leads to strange page layouts and uses other algorithms e.g.
> Reed-Solomon, so the generic mkyaffs - generate everything - will not
> work anymore.
>
> As we discussed before the only way to solve this is ECC autoplacement,
> which is unfortunately not possible with YAFFS1 although it could be
> tweaked to use it. YAFFS2 uses autoplacement ?

It would be quite simple to modify YAFFS1 to work with autoplacement. YAF=
FS2=20
uses autoplacement.

>
> To provide images which can be programmed into the FLASH during
> manufacturing you will need a different approach.
>
> - mkyaffs provides the filesystem data
>
> - an ecc generator which must be aware of the algortihm and the
> placement builds the final image which can be programmed to the chip
>
> - If you can programm it from the OS, then you can read the image back
> from the chip and you do not need a software emulation of the ecc and
> placement
>
> tglx
>
>
>
> _______________________________________________
> yaffs mailing list
> yaffs@stoneboat.aleph1.co.uk
> http://stoneboat.aleph1.co.uk/cgi-bin/mailman/listinfo/yaffs