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

[Koen Vandeputte]

On 20.10.18 17:46, Hauke Mehrtens wrote:
> 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
Very good point.
I've requested Mikrotik this morning to provide some details about the 
actual chips being used since the launch of that board ..

tbc

Koen


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