Hi Pavel, On Wed, 7 Mar 2018 23:17:33 +0100 Pavel Machek <pavel@xxxxxx> 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