linux-kernel - Re: [PATCH] mtd: brcmnand: Workaround false ECC uncorrectable errors

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Message-ID: <565F62C7.8010009@simon.arlott.org.uk>
Date:	Wed, 2 Dec 2015 21:29:43 +0000
From:	Simon Arlott <simon@...e.lp0.eu>
To:	Jonas Gorski <jogo@...nwrt.org>,
	Brian Norris <computersforpeace@...il.com>
Cc:	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Kamal Dasu <kdasu.kdev@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
	MTD Maling List <linux-mtd@...ts.infradead.org>,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] mtd: brcmnand: Workaround false ECC uncorrectable errors

On 02/12/15 21:08, Jonas Gorski wrote:
> On Wed, Dec 2, 2015 at 9:54 PM, Brian Norris
> <computersforpeace@...il.com> wrote:
>>
>> BTW, I think Kamal had code to handle protecting bitflips in erased
>> pages code in the Broadcom STB Linux BSP. Perhaps he can port that to
>> upstream with nand_check_erased_ecc_chunk()? IIUC, that would probably
>> handle your case too, Simon, although it wouldn't be optimal for an
>> all-0xff check (i.e., bitflip_threshold == 0).
>>
>> If that's really an issue (i.e., we have an implementation + data), I'm
>> sure we could add optimization to nand_check_erased_ecc_chunk() to
>> support the bitflip_threshold == 0 case.
> 
> Maybe I'm missing something, but wasn't the point of introducing
> nand_check_erased_ecc_chunk that bitflips in erased pages should be
> treated as bitflips corrected by the ecc, and therefore fixed up
> before passing the data further on? So having a theshold of 0 would be
> wrong / no protection at all, and could be quite destructive on MLC
> nand, where bitflips in erased pages are rather common.

Without this patch I can't access erased pages at all. I don't know if
the controller will still return an uncorrectable error if the page is
erased but has 1 or more bit flips.

-- 
Simon Arlott
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