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

[Hauke Mehrtens]

On 10/18/2018 02:28 PM, Koen Vandeputte 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.
> 
> 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

Have you checked if these are really MLC chips or if they are just
getting detected wrongly?
I think I saw some SPI NAND chips which a patched Linux detected as MLC
but the datasheet said they are SLC chips.

Hauke

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