MLC NAND support in ubifs

[Filip Kubicz]

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.

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.

Kind regards,
Filip Kubicz

filip at kubicz.engineer
tel. (+48) 697 088 078