NAND / BCH and DMA?

[Arkadi Shishlov]

Hi,

it looks like much of the perceived Linux slowness on CI20 NAND is due to BCH driver using PIO? Or is it UBI/FS?

Is there a fundamental limitation of NEMC / BCH or MTD that requires CPU to read / write each data word or this could be changed to use DMA engine / driver?

I wrote some (proprietary) drivers in Linux v2.0 days, but complete lost touch with the kernel developments after v2.4.9. It's much more complicated set of frameworks now, but I may want to play with it on 3.18 or 6.1 if speed improvement is realistic. The only doc I have is JZ4780 Programming Manual though (JZ4780_pm.pdf).

[H. Nikolaus Schaller]

Hi,

I am running my CI20 from an SD card with 6.2-rc8 kernel which seems to use DMA. No slowness issues.

AFAIR there is no NAND driver any more. It was removed years ago because the author thought that it can't work anyways.

BR,

Nikolaus

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[Arkadi Shishlov]

On Tuesday, 14 February 2023 at 14:35:12 UTC+2 H. Nikolaus Schaller wrote:

Hi,

I am running my CI20 from an SD card with 6.2-rc8 kernel which seems to use DMA. No slowness issues.

AFAIR there is no NAND driver any more. It was removed years ago because the author thought that it can't work anyways.

Yep, SD is totally fine, running Buildroot image from SD here.

I reverted ubi: Reject MLC NAND [1] patch and UBIFS works for me. Interesting insights in the thread.

My question is mostly in 3.18 CI20_Linux context, as that what I stubbornly run from MTD for desktop experience. (cache is on SD)

1. https://lore.kernel.org/lkml/20180303104554...@nod.at/