Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756871AbbLBUym (ORCPT ); Wed, 2 Dec 2015 15:54:42 -0500 Received: from mail-pf0-f169.google.com ([209.85.192.169]:34877 "EHLO mail-pf0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756653AbbLBUyS (ORCPT ); Wed, 2 Dec 2015 15:54:18 -0500 X-Greylist: delayed 8124 seconds by postgrey-1.27 at vger.kernel.org; Wed, 02 Dec 2015 15:54:18 EST Date: Wed, 2 Dec 2015 12:54:15 -0800 From: Brian Norris To: Jonas Gorski Cc: Simon Arlott , Florian Fainelli , Kamal Dasu , Linux Kernel Mailing List , MTD Maling List , bcm-kernel-feedback-list , David Woodhouse , Boris Brezillon Subject: Re: [PATCH] mtd: brcmnand: Workaround false ECC uncorrectable errors Message-ID: <20151202205415.GQ64635@google.com> References: <5659FF4A.7080203@simon.arlott.org.uk> <565F51D2.4010204@simon.arlott.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2453 Lines: 57 Hi, On Wed, Dec 02, 2015 at 09:44:04PM +0100, Jonas Gorski wrote: > 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 Hamming only protects 1 bitflip. The '15' is the value used by the controller to represent Hamming (i.e., there is no BCH-15). > 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. 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. Brian -- 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/