[OpenWrt-Devel] [PATCH] kernel: tolerate using UBI/UBIFS on MLC flash (FS#1830)

[Rafał Miłecki]

On Thu, 18 Oct 2018 at 14:29, Koen Vandeputte
<koen.vandeputte at ncentric.com> wrote:
> starting from upstream commit 577b4eb23811 ("ubi: Reject MLC NAND")
> it is not allowed to use UBI and UBIFS on a MLC flavoured NAND flash chip. [1]
>
> According to David Oberhollenzer [2]:
>
> The real problem is that on MLC NAND, pages come in pairs.
>
> Multiple voltage levels inside a single, physical memory cell are used to
> encode more than one bit. Instead of just having pages that are twice as big,
> the flash exposes them as *two different pages*. Those pages are usually not
> ordered sequentially either, but according to a vendor/device specific
> pairing scheme.
>
> Within OpenWrt, devices utilizing this type of flash,
> combined with ubi(fs) will be bricked when a user upgrades
> from 17.01.4 to a newer version as the MLC will be refused.

We should disable building images for those unsupported devices. Could
you provide a list of devices using MLC & "supported" by OpenWrt,
please? Or even better a patch disabling images for them?


> As these devices are currently advertised as supported by OpenWrt,
> we should at least maintain the original state during the lifecycle
> of the current releases.
>
> Support can be gracefully ended when a new release-branch is created.
>
> Signed-off-by: Koen Vandeputte <koen.vandeputte at ncentric.com>
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v4.14.77&id=577b4eb23811dfc8e38924dc476dbc866be74253
> [2] https://lore.kernel.org/patchwork/patch/920344/
> ---
>
> Mainly intended for discussion first on this approach before applying it.
> Can be cherrypicked to 18.06.
>
> Feel free to drop your (n)ack on this approach

Well, MAYBE, we could push this to the openwrt-18.06. I'm not sure
about this. Upstream developers decided to drop MLC support completely
even for stable kernels (Cc: stable@).

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