From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.bootlin.com ([62.4.15.54]) by bombadil.infradead.org with esmtp (Exim 4.89 #1 (Red Hat Linux)) id 1ethah-0006pd-So for linux-mtd@lists.infradead.org; Wed, 07 Mar 2018 22:31:22 +0000 Date: Wed, 7 Mar 2018 23:30:57 +0100 From: Boris Brezillon To: Pavel Machek Cc: David Woodhouse , Greg KH , Steve deRosier , Richard Weinberger , Boris Brezillon , dedekind1@gmail.com, tharvey@gateworks.com, linux-kernel@vger.kernel.org, stable@vger.kernel.org, marek.vasut@gmail.com, linux-mtd@lists.infradead.org, cyrille.pitchen@wedev4u.fr, computersforpeace@gmail.com Subject: Re: [PATCH] ubi: Reject MLC NAND Message-ID: <20180307233057.54bd35c3@bbrezillon> In-Reply-To: <20180307221733.GE10438@amd> References: <20180303104554.5958-1-richard@nod.at> <20180306231805.GA28183@amd> <6772577.AmT7QaWTNU@blindfold> <20180307214342.GA9852@amd> <1520460673.31298.136.camel@infradead.org> <20180307221733.GE10438@amd> 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: , Hi Pavel, On Wed, 7 Mar 2018 23:17:33 +0100 Pavel Machek wrote: > On Wed 2018-03-07 22:11:13, David Woodhouse wrote: > > > > > > On Wed, 2018-03-07 at 14:08 -0800, Steve deRosier wrote: > > > > > > To clarify one thing: the reason for this is MLC has actually never > > > been supported, nor worked properly. The fact that it kinda worked was > > > incidental and the cause of major problems for people due to that not > > > being clear. This patch only makes it explicit and avoids people > > > mistakenly trying to use UBIFS on MLC flash and risking their data and > > > products. To me, that's what's important. > > > > > > This is an important patch, even if all it does is keep people from > > > loosing data. It also changes the conversation from "I have a > > > corrupted UBIFS device, BTW it's on MLC..." to "What can we do to get > > > UBIFS to work on MLC". > > Well, for -stable I'd suggest printk(KERN_ALERT ...) but keep the > system running. > > > This is a bug fix. > > > > UBI on MLC never worked. It was a bug that we ever permitted it. This > > is now fixed. > > Yeah, well, so lets say I have a working hardware (maybe using > read-only UBI on MLC), update to next stable kernel, and now kernel > refuses to see the partition. Read-only does not save you from the read-disturb issue, and you even have to take care of programming the full erase-block on some MLC NANDs, which AFAIR is not done when updating a static volume. I have one simple question: did you ever play with MLC NANDs or are you just trolling? If you had, like Richard and I did when working on MLC support, I'm pretty sure you wouldn't play this "don't backport to stable" card. Now, if you volunteer to add reliable MLC support, I can send you a few boards to play with. I even have a "working but not so tested PoC" here [1] if you want to finish the job, but please don't do the mistake of thinking the fix is that simple. > > I'll certainly not consider this patch a bug fix. And apparently a lot of people disagree with you on this point, and I guess all of them had problems with MLC NANDs. > > Removing support for hardware that "only works by mistake" may be good > idea, but maybe it is slightly too surprising for a -stable. I wouldn't say "work by mistake" but "seems to work at first but in the end breaks", so definitely a candidate for -stable IMO. Regards, Boris [1]https://github.com/bbrezillon/linux/tree/nand/mlc -- Boris Brezillon, Bootlin (formerly Free Electrons) Embedded Linux and Kernel engineering https://bootlin.com