From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753578Ab3KYMaF (ORCPT ); Mon, 25 Nov 2013 07:30:05 -0500 Received: from top.free-electrons.com ([176.31.233.9]:44932 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751128Ab3KYMaD (ORCPT ); Mon, 25 Nov 2013 07:30:03 -0500 Date: Mon, 25 Nov 2013 09:30:13 -0300 From: Ezequiel Garcia To: David Woodhouse Cc: Hans Zhang , Richard Genoud , linux-mtd , "linux-kernel@vger.kernel.org" , zhouguangming@innofidei.com Subject: Re: [PATCH] Make the mtdblock read/write skip the bad nand sector Message-ID: <20131125123012.GE2408@localhost> References: <528EB1E3.7030101@innofidei.com> <20131122015237.GB3509@localhost> <528EBD0B.5010006@innofidei.com> <20131122114509.GB2414@localhost> <5292A7E7.5060003@innofidei.com> <20131125101147.GA2408@localhost> <529334D9.2030204@innofidei.com> <20131125115238.GC2408@localhost> <1385381770.24518.18.camel@shinybook.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1385381770.24518.18.camel@shinybook.infradead.org> 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 David, On Mon, Nov 25, 2013 at 12:16:10PM +0000, David Woodhouse wrote: > On Mon, 2013-11-25 at 08:52 -0300, Ezequiel Garcia wrote: > > > > Your understanding is correct: NAND *must* be erased explictly in > > userspace > > before writing. However, keep in mind the following additional > > constraints: > > > > * Writing should be always performed using 'nandwrite', > > not tools such as 'cat' or 'dd'. > > > > * An mtdblock shouldn't be used to access directly the NAND from > > userspace. AFAICS, the primarily usage of mtdblock is to be able to > > mount JFFS2. > > No. You don't need mtdblock to mount JFFS2 at all. > > The mtdblock driver was used in the *very* early days of the MTD system, > on NOR flash with a "traditional" file system. Either in read-only mode > for something like cramfs, or in a very unsafe writeable mode. We > actually put ext2 on it for the Compaq iPaq for a while, before we had > JFFS. > > It was used as a shortcut for mounting JFFS2, and still is by a lot of > people, but it's certainly not necessary. You can turn off CONFIG_BLOCK > entirely and still use JFFS2. > > You should consider mtdblock to be the most basic, primitive, "flash > translation layer" that can possibly exist. And thus, should basically > never use it. I certainly don't approve of trying to extend it. > Thanks a lot for the insight. After reading this, I'm wondering what's preventing us from killing MTD block support altogether. Artem, already suggested it a while back... -- Ezequiel García, Free Electrons Embedded Linux, Kernel and Android Engineering http://free-electrons.com