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

[Koen Vandeputte]

On 22.10.18 19:27, Christian Lamparter wrote:
> On Monday, October 22, 2018 3:48:29 PM CEST Koen Vandeputte wrote:
>> 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 ..
> For the RB450/G you can take a look at the User Guide on their side:
> <https://mikrotik.com/product/RB450G#fndtn-downloads>
> <https://i.mt.lv/cdn/rb_files/rb450GugA.pdf>
>
> On Page 3 there's a "System Board View" with a bottom view of the PCB
> and this is where the NAND chip is located. It reads:
>
> HY27UT084G2A
>
> This translates to:
> <http://natisbad.org/NAS/refs/Hynix_NAND_flash_part_number_decoding.pdf>
>
> HY27UT084G2A
>    ||||
>    |||^--- T = MLC + Single Die + Large Block
>    ||^---U = 2.7V~3.6V
>    |^---7 = NAND FLASH
>    ^---2 = FLASH
>   
> So, it is NAND MLC FLASH.
>
Received a reply from Mikrotik tech dept.:


Hello,

Mainly there are two possible NAND chips for RB450G:
W29N04GVSIAA (see attachment);
MT29F4G08ABADAWPD.

Can you provide some device serial numbers?


Best regards,
Elans L.




Checking the datasheets from both chips mentioned above shows they are both SLC flash.
@Christian, do you have this board?  Could you provide the serial?


Thanks,

Koen


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