Hi Pavel,
On Wed, 7 Mar 2018 23:17:33 +0100 Pavel Machek pavel@ucw.cz 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