From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.free-electrons.com ([62.4.15.54]) by bombadil.infradead.org with esmtp (Exim 4.87 #1 (Red Hat Linux)) id 1d96DR-00040z-97 for linux-mtd@lists.infradead.org; Fri, 12 May 2017 08:46:28 +0000 Date: Fri, 12 May 2017 10:45:54 +0200 From: Boris Brezillon To: Mario Rugiero Cc: Richard Weinberger , "linux-mtd@lists.infradead.org" Subject: Re: [PATCH] mtd: nand: add option to erase NAND blocks even if detected as bad. Message-ID: <20170512104554.5670bb4d@bbrezillon> In-Reply-To: References: <20170512053957.10426-1-mrugiero@gmail.com> <20170512102407.217b805a@bbrezillon> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Fri, 12 May 2017 05:34:10 -0300 Mario Rugiero wrote: > 2017-05-12 5:24 GMT-03:00 Boris Brezillon : > > On Fri, 12 May 2017 05:16:08 -0300 > > Mario Rugiero wrote: > > > >> 2017-05-12 5:12 GMT-03:00 Richard Weinberger : > >> > Mario, > >> > > >> > On Fri, May 12, 2017 at 7:39 AM, Mario J. Rugiero wrote: > >> >> Some chips used under a custom vendor driver can get their blocks > >> >> incorrectly detected as bad blocks, out of incompatibilities > >> >> between such drivers and MTD drivers. > >> >> When there are too many misdetected bad blocks, the device becomes > >> >> unusable because a bad block table can't be allocated, aside from > >> >> all the legitimately good blocks which become unusable under these > >> >> conditions. > >> >> This adds a build option to workaround the issue by enabling the > >> >> user to free up space regardless of what the driver thinks about > >> >> the blocks. > >> > > >> > Hmm, this sounds like a gross hack. > >> It is, but I see no other solution. The NAND chips were used in an > >> incompatible way by a hack-n-slash driver made by allwinner, and > >> trying to load them with a proper MTD driver fails miserably if this > >> is not done. > >> If anyone can propose a better solution I'll more than happily implement it. > >> I'm open to suggestions, and of course I'm open to rejection of my > >> patches if needed. > > > > u-boot provides the nand.scrub command, which does exactly what you're > > looking for. And no, I don't think it's a good idea to allow erasing > > bad blocks, at least not by default. > > > > If we really want to support this feature in linux, this should be > > explicitly enabled through debugfs. > If I do this, does it stand a chance at getting upstream? > If so, I'll have it done soon. > Note however that the build option is disabled by default. I get that > there should also be one runtime option, disabled by default, exposed > through debugfs. Does that sound right? > > > >> > > >> >> Example usage: recovering NAND chips on sunxi devices, as explained > >> >> here: http://linux-sunxi.org/Mainline_NAND_Howto#Known_issues > >> > > >> > What this wiki suggests is not wise. > >> > How can you know which blocks are really bad and which not? > >> You don't, at least not without an even grosser hack implementing read > >> support for their incompatible format. > >> Would that be better? I might attempt it if desired. > > > > No, please don't do that, at least not in the kernel. If you really > > want to parse the old format, you should develop a tool that reads NAND > > pages in raw mode, stores the list of bad blocks somewhere and then > > re-use this list to select which blocks should be forcibly erased. > > > > Not sure it's worth the pain :-). > It's worth the pain to me. I'm dealing with a bit rotten 3.4 based > pile of cr*p on production because of this. Whatever I have to do to > get those machines running the mainline kernel is worth it. No, I meant, doing that vs scrubbing the NAND. Note that MLC support is not reliable in mainline, so I'd strongly discourage to use a mainline kernel right now, unless you have an SLC NAND.