Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756735AbbLBUod (ORCPT ); Wed, 2 Dec 2015 15:44:33 -0500 Received: from arrakis.dune.hu ([78.24.191.176]:40198 "EHLO arrakis.dune.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752008AbbLBUoa (ORCPT ); Wed, 2 Dec 2015 15:44:30 -0500 MIME-Version: 1.0 In-Reply-To: <565F51D2.4010204@simon.arlott.org.uk> References: <5659FF4A.7080203@simon.arlott.org.uk> <565F51D2.4010204@simon.arlott.org.uk> From: Jonas Gorski Date: Wed, 2 Dec 2015 21:44:04 +0100 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] mtd: brcmnand: Workaround false ECC uncorrectable errors To: Simon Arlott Cc: Florian Fainelli , Kamal Dasu , Linux Kernel Mailing List , MTD Maling List , bcm-kernel-feedback-list , Brian Norris , David Woodhouse Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1686 Lines: 41 On Wed, Dec 2, 2015 at 9:17 PM, Simon Arlott wrote: > On 01/12/15 10:41, Jonas Gorski wrote: >> On Sat, Nov 28, 2015 at 8:23 PM, Simon Arlott wrote: >>> + >>> + /* Go to start of buffer */ >>> + buf -= FC_WORDS; >>> + >>> + /* Erased if all data bytes are 0xFF */ >>> + buf_erased = memchr_inv(buf, 0xFF, FC_WORDS) == NULL; >>> + >>> + if (!buf_erased) >>> + goto out_free; >> >> We now have a function exactly for that use case in 4.4, >> nand_check_erased_buf [1], consider using that. This also has the >> benefit of treating bit flips as correctable as long as the ECC scheme >> is strong enough. > > I have no idea whether or not it's appropriate to specify > bitflips_threshold > 0 so it'd just be a more complex way to do > a memchr_inv() search for 0xFF. The threshold would be the amount of bitflips the code can correct, so basically ecc.strength (at least that is my understanding). > The code also has to check for the hamming code bytes being all 0x00, > because according to the comments [2], the controller also has > difficulty with the non-erased all-0xFFs scenario too. According to brcmnand.c hamming can fix up to fifteen bitflips, but in the current code you would fail a hamming protected all-0xff-page for even a single bitflip in the data or in the ecc bytes, which means that all-0xff-pages wouldn't be protected at all. Jonas -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/