4bit NAND ECC

4bit NAND ECC

[Dennis Millard]

Anyone who has worked with NAND ECC support, I have a question-

    I have a platform running the 2.6.30 kernel based on the Marvell 
88F6281.  It has 512 MB NAND flash, and is very similar to the Marvell 
Sheevaplug reference design.  My Uboot is using 4bit NAND ECC to write 
the kernel and ramdisk to flash.  However, I recently discovered that 
the 2.6.30 kernel does not support 4bit ECC mode.  When I try to access 
the Uboot environment variables from the running kernel, I can only use 
1bit ECC.  When I switch Uboot to use 1bit ECC, I get lots of errors 
while accessing the Uboot vars in flash.  I've been told that I really 
should be using 4bit ECC in Uboot.

    I noticed that the 2.6.32 kernel supports 4bit ECC, but it appears 
to be only for the TI DaVinci CPU.  Can someone confirm this?  Does this 
mean that 4bit ECC is not available for general use in the 2.6.32 
kernel?  Does anyone know of a patch that would make it available for 
the Marvell 88F6281?

Thanks-
  Dennis Millard

Re: 4bit NAND ECC

[Nicolas Pitre]

On Thu, 17 Dec 2009, Dennis Millard wrote:

> Anyone who has worked with NAND ECC support, I have a question-
> 
>    I have a platform running the 2.6.30 kernel based on the Marvell 88F6281.
> It has 512 MB NAND flash, and is very similar to the Marvell Sheevaplug
> reference design.  My Uboot is using 4bit NAND ECC to write the kernel and
> ramdisk to flash.  However, I recently discovered that the 2.6.30 kernel does
> not support 4bit ECC mode.  When I try to access the Uboot environment
> variables from the running kernel, I can only use 1bit ECC.  When I switch
> Uboot to use 1bit ECC, I get lots of errors while accessing the Uboot vars in
> flash.  I've been told that I really should be using 4bit ECC in Uboot.
> 
>    I noticed that the 2.6.32 kernel supports 4bit ECC, but it appears to be
> only for the TI DaVinci CPU.  Can someone confirm this?  Does this mean that
> 4bit ECC is not available for general use in the 2.6.32 kernel?  Does anyone
> know of a patch that would make it available for the Marvell 88F6281?

The Davinci 4-bit ECC support is about hardware ECC.

I'm sitting on software 4-bit ECC code that I still have to integrate 
with the MTD code at some point.

And you should really avoid using flash for ramdisks.  Better use 
JFFS2 or UBIFS directly rather than using a ramdisk.


Nicolas