MLC NAND support in ubifs

[Richard Weinberger]

On Mon, Sep 20, 2021 at 9:39 PM Filip Kubicz <filip at kubicz.engineer> wrote:
>
> Hi All,
>
> I'm bumping up the question about NAND support since it looks like it slipped unnoticed between emails with patches. Does anyone know the answer?
>
> Thank you in advance,
> Filip
>
> filip at kubicz.engineer
> tel. (+48) 697 088 078
>
>
> ---- On Thu, 09 Sep 2021 18:41:24 +0200 filip at kubicz.engineer  wrote ----
>
>  > Hi!
>  >
>  > I would like to ask about MLC NAND support in UBIFS.
>  >
>  > I was recently bringing up a device with IMX6ULL and raw MLC NAND flash. I have built Linux 5.4 kernel, u-boot and rootfs (using buildroot), flashed them to my device with MLC NAND flash, and learned from dmesg error that MLC is unsupported by ubifs. Support removed in this commit: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b5094b7f135be
>  >
>  > Then I followed the story from Richard and Boris and watched the talk where they explain the issues with MLC, and propose an alternative: https://www.youtube.com/watch?v=9j2pOIiJqYw&ab_channel=TheLinuxFoundation
>  > Alternative available since Linux 5.8: https://www.phoronix.com/scan.php?page=news_item&px=Linux-5.8-NAND-MLC-SLC-Emulate
>  >
>  > My questions:
>  > 1. Is NAND MLC (+ubifs) reliable to use with SLC emulate mode introduced in kernel 5.8? Or should I rather switch to eMMC for this design? SLC NAND is too costly at my required size.

SLC emulation solves only the paired pages problem. You still get all
other downsides of MLC. I'd not use it unless I'm forced to.

>  > 2. If the MLC NAND is not supported, can you update these pages:
>  > - http://www.linux-mtd.infradead.org/doc/ubifs.html
>  > - https://www.kernel.org/doc/html/latest/filesystems/ubifs.html
>  > - http://www.linux-mtd.infradead.org/faq/ubifs.html
>  > Each of the documentation pages mention MLC, so you can get an idea that it is supported. But it looks like the MLC NAND flash is not supported by UBIFS.

Good point!

-- 
Thanks,
//richard