linux-kernel - Re: [PATCH] ubi: Reject MLC NAND

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Message-ID: <20180307221733.GE10438@amd>
Date:   Wed, 7 Mar 2018 23:17:33 +0100
From:   Pavel Machek <pavel@....cz>
To:     David Woodhouse <dwmw2@...radead.org>, Greg KH <greg@...ah.com>
Cc:     Steve deRosier <derosier@...il.com>,
        Richard Weinberger <richard@....at>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        dedekind1@...il.com, tharvey@...eworks.com,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        marek.vasut@...il.com, linux-mtd@...ts.infradead.org,
        cyrille.pitchen@...ev4u.fr, computersforpeace@...il.com
Subject: Re: [PATCH] ubi: Reject MLC NAND

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.

I'll certainly not consider this patch a bug fix.

Removing support for hardware that "only works by mistake" may be good
idea, but maybe it is slightly too surprising for a -stable.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html