From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-db8lp0188.outbound.messaging.microsoft.com ([213.199.154.188] helo=db8outboundpool.messaging.microsoft.com) by merlin.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1ULoX9-0003yo-2w for linux-mtd@lists.infradead.org; Sat, 30 Mar 2013 05:40:56 +0000 Message-ID: <51567AD3.5030704@caviumnetworks.com> Date: Fri, 29 Mar 2013 22:40:35 -0700 From: Aaron Williams MIME-Version: 1.0 To: Ivan Djelic Subject: Re: MTD NAND BCH support for 24 bits/1K of ECC correction? References: <5154C2C5.5000903@caviumnetworks.com> <20130329090219.GB6928@parrot.com> In-Reply-To: <20130329090219.GB6928@parrot.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-mtd@lists.infradead.org, "linux-kernel@vger.kernel.org" List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 03/29/2013 02:02 AM, Ivan Djelic wrote: > On Thu, Mar 28, 2013 at 10:23:01PM +0000, Aaron Williams wrote: >> Hi all, >> >> I am trying to clean up our OCTEON NAND flash driver in the Linux kernel >> and enable support for multi-bit ECC using BCH and am having some >> issues. I am able to successfully work with NAND flash that requires 4 >> bits ECC per 512 bytes but I am having issues with one of our boards >> that has a NAND device that requires 24 bits of ECC per 1024 bytes. >> >> I was wondering if ECC of this magnitude has been successfully tested in >> the past. By my calculations I should have 42 bytes of ECC per 1K block >> (m=14, t=24 for 336 bits of ECC data). My problem is that when decoding >> an encoded block I am seeing that nroots != err in decode_bch() after >> find_poly_roots(). I am seeing this for all of the blocks I attempt to >> read. As far as I can tell the data being sent to BCH is good, though it >> might have a few bad bits but nowhere near 24. >> >> I am also seeing this same behavior in my U-Boot code which uses the >> identical bch and nand_bch code. >> > Hi Aaron, > > CC-ing your message to linux-mtd which is the place to go for such questions :-) > > Your configuration (m=14 t=24 with 1024 bytes of data) has been tested, and should work > with the BCH library. Could you give some details about your ECC setup: > > 1. Are you trying to locate and correct errors from hardware-computed syndromes ? > > 2. If yes, did you provide the BCH lib with the specific primitive polynomial used by > your hardware ? What is this polynomial ? > > 3. Could you provide the ECC bytes generated for the following block patterns: > - a 0xff-filled 1024 bytes block > - a 0xff-filled 1024 bytes block, except for the first byte set to 0xfe > This would help me find out how to setup the library to match your hardware. > > Regards, We are doing the BCH support entirely in software due to limitations of our hardware to 1 bit ECC. I may have to get back to you. I may have found the problem and will try and look at it some more next week. It looks like I now have it working in U-Boot and the same bug exists in our Linux driver. It wouldn't be the first one... our NAND drivers haven't been updated in ages. -Aaron -- Aaron Williams Software Engineer Cavium, Inc. (408) 943-7198 (510) 789-8988 (cell)