Eugene,

Thanks for the tip. It is a pity I have to verify content because our hardware cannot help me here, but it may be not a big deal since I have to do it only in case of an uncorrectable error.

One question though - are you saying yaffs may decide to retire a block based on _corrected_ errors reported by mtd? I know nand layer (I am on 2.6.26.8) returns -EUCLEAN on corrected error, but I see that yaffs treats it as any other error. Our hardware has pretty strong ecc block - up to 6 bit errors per 512 byte chunk. I would hate to waste that capability.
So where is the threshold where I need to report correctable errors? Maybe I should not do it at all?

Regards,
Max

949-483-9081 (office)
949-483-9414 (lab)

-----Original Message-----
From: Eugene Surovegin [mailto:ebs@ebshome.net]
Sent: Thursday, July 01, 2010 7:57 AM
To: Max Rayskiy
Cc: 'yaffs@lists.aleph1.co.uk'
Subject: Re: [Yaffs] Failure to write to an erased flash due to yaffs_CheckChunkErased failure

On Wed, Jun 30, 2010 at 11:19:07AM -0700, Max Rayskiy wrote:
> Hello,
>
> I am developing a NAND driver for an SOC and trying to use YAFFS2 with it. Our proprietary flash controller has hardware ECC support. One problem I cannot find a solution for is how to tell yaffs to ignore ECC errors when reading pages from erased blocks.
> I am getting a request for full page read with tags, and obviously for
> an erased block I have to return that there were uncorrectable ECC
> errors. I would assume that yaffs should be able to tell erased block
> from real ECC failure. But all I am getting is messages like

I have written MTD driver for a similar controller, and I deal with this in the driver itself - on uncorrectable ECC error I verify contents of that page, and if it's all 0xff I don't report ECC errors to the upper levels. You also probably shouldn't report 1-bit correctable ECC errors if hw ECC is much stronger (say it can correct 3 bit erros per 512 byte chunk) - 1-bit errors are frequent enough so after several weeks or months, YAFFS will retire a lot of blocks without any good reason.

--
Eugene


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