mtd, mtdblock and nand ecc.

[Thomas Gleixner]

On Wednesday 14 April 2004 18:49, David Daney wrote:
> >
> >He ? 1 minute ? Where is the time spent ?
> How should I know?

Profiling :)

> >Thats totaly out of the usual time. My boot time with JFFS2 is well below
> > 30s on an ARM7. I have no YAFFS root fs handy, but it is much faster.
> >
> >The solution is checking where the time is lost and fixing it.
>
> I have a custom nand driver (based on nand.c, but adapted to a non
> standard nand physical interface) that uses software ECC.  On a 300 MHz
> mips32 cpu.

Why did you modify nand.c ? 
Almost everything in nand.c can be overridden by the board driver. Therefor we 
call all the functions through chip->xxx().

> When ever jffs2 or yaffs are mounted, they both seem to read many
> pages.  Perhaps the ECC overhead of reading all that data.
> I suppose I could turn off ECC and see how fast it is...

Sure, that would give an estimation.

> >>That is why I am thinking about using a non NAND aware file system for
> >>things that can be read-only.
> >
> >But this does not answer my question how you want to deal with bad blocks
> > ?
>
> I want a file system very much like cramfs, but that can have holes in
> it so that it works on NAND.
> When mounted it would start scanning blocks starting from the beginning
> of the NAND partition until it found a valid superblock (or what ever
> you would call it).  Then it would be done because all of the indexes
> would be built to work around the bad blocks.  Since this filesystem
> would be read-only with a static structure, you would never have to read
> more than necessary.

OK, so you are going to write a fs driver, which is NAND aware and behaves 
similar to cramfs. 
Whatfor then the discussion about making mtdblock nand aware ?
If you write a nand aware fs then you just call the appropriate functions. 
This fs will be specific for nand or selectable for nand, so what ?
No need to touch anything in mtdblock.c

-- 
Thomas
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