Re: [PATCH 2/4] Fine split S3C arch dependencies from generic code

From: Juergen Beisert <jbe@pengutronix.de>
To: barebox@lists.infradead.org
Cc: Alexey Galakhov <agalakhov@gmail.com>
Subject: Re: [PATCH 2/4] Fine split S3C arch dependencies from generic code
Date: Fri, 4 May 2012 14:00:18 +0200	[thread overview]
Message-ID: <201205041400.18168.jbe@pengutronix.de> (raw)
In-Reply-To: <4FA3C036.3050706@gmail.com>

Alexey Galakhov wrote:
> On 04.05.2012 17:13, Juergen Beisert wrote:
> > AFAIR the MLC ECC generator is different in its handling. At least it is
> > much slower than the 1 bit ECC generator and so the routines must wait
> > the result to continue on the block data.
>
> Correct.
>
> This is achieved by adding register polling loop at the beginning of
> corresponding calculate() function. The rest of function is almost the
> same, just the number of ECC bytes is larger.
>
> The S3C2440 has a hardware ECC corrector which we do not use yet.

AFAIK only a hardware ECC _calculator_, but no correction unit. It must be 
done in software.

> >> I suggest to support both new and old hardware in the same code. Why
> >> not? It is 95% the same.
> >
> > Instead of making the S3c2440 NAND driver more and more complicated (what
> > is the benefit of all in one driver?) I would vote for fading it out (as
> > its hardware do not change anymore). And creating a new driver for all
> > more recent CPUs with MLC support.
> >
> > My idea was also to not support simple ECC on these newer CPUs anymore.
> > Using the 8 bit reed-solomon checksum would be an improvement for SLCs as
> > well (and also their OOB sizes are large enough to store the 8 bit
> > checksums). And at least if we want to boot from NAND we cannot continue
> > to use simple ECC checksums anymore.
>
> Maybe that's right. But simple ECC support is very simple anyway,
> harmless to keep.

Or _useless_ to keep ;)

> And looks like some low-cost Chinese boards still have SLC even with newer
> CPUs.

The better the checksum the saver your NAND data content is. That is why I 
want to use reed-solomon checksums even for SLCs (and keep in mind: you 
_must_ use 8 bit reed-solomon checksums if you want to boot from NAND).

> [...]
> BTW, do we want software ECC support too?

No. Nobody needs it and nobody wants it (ways to slow).

jbe

-- 
Pengutronix e.K.                              | Juergen Beisert             |
Linux Solutions for Science and Industry      | http://www.pengutronix.de/  |

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