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

[Christian Lamparter]

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.



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