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Date: Wed, 08 Jan 2014 08:29:32 +0100
From: Stefan Roese <sr@denx.de>
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Subject: Re: [RFC/PATCH] mtd: mtd_read: Fix bitflips_threshold comparison
 to allow max bitflips
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Cc: Brian Norris <computersforpeace@gmail.com>, Pekon Gupta <pekon@ti.com>
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On 30.12.2013 13:40, Stefan Roese wrote:
> On a custom AM335x based platform with a Toshiba NAND device
> (TC58NVG1S3H) we are currently seeing quite a few of these UBI messages:
> 
> [   18.044967] UBI: fixable bit-flip detected at PEB 50
> [   18.050252] UBI: schedule PEB 50 for scrubbing
> ...
> 
> After a bit debugging I found that those messages are only printed when
> the OMAP NAND driver has detected 8 (corrected) bitflips / 512 bytes on
> a read. We're using HW BCH8 and the Toshiba chip supports 8 bit ECC for
> each 512Byte. I was wondering why 8 bitflips resulted in these UBI
> messages and e.g. 7 bitflips didn't. Hence I discovered the comparison
> "ret_code >= mtd->bitflip_threshold" in mtd_read().
> 
> With this patch applied all tests (UBIFS) I've done so far didn't produce
> any of these "UBI: fixable bit-flip" messages any more.
> 
> Note that I'm sending this patch as RFC for now. To get some feedback
> from other MTD / NAND developers on this issue. The main question is:
> Should mtd_read() return -EUCLEAN if the corrected bitflips are equal to
> the bitflip-threshold value? Or should it return 0 since the bitflips
> have been corrected?

Brian, do you have any comments? Is this patch good as is? Should I
resend it as non-RFC?

Thanks,
Stefan