[RFC] Change ECC algorithm from userspace

[Atlant Schmidt]

Javier:

  That's why most people boot from NOR Flash
  where a 1-bit ECC is adequate.

  I don't see how you can possibly expect to
  reliably, successfully boot from a NAND Flash
  using just 1 bit ECC; you've either got to
  change the boot loader to allow more ECC or
  use more-reliable Flash hardware.

                            Atlant

-----Original Message-----
From: linux-mtd-bounces at lists.infradead.org [mailto:linux-mtd-bounces at lists.infradead.org] On Behalf Of Javier Martinez Canillas
Sent: Friday, October 28, 2011 05:43
To: linux-mtd at lists.infradead.org; linux-omap at vger.kernel.org
Cc: Enric Balletbo i Serra
Subject: [RFC] Change ECC algorithm from userspace

Hello,

We've a custom board using an ARM OMAP DM3730 whose ROM boot loader
only supports 1-bit ECC correction using Hamming algorithm.

So, in order to be able to boot from the NAND, we have to configure
the GPMC (OMAP's memory controller that interfaces with NAND devices)
to use 1-bit HW ECC and write the loader binary to the first NAND
sector. That way the ROM boot will take this sector as valid and load
the loader binary to RAM.

The problem is that the SLC NAND device that we are using has a
minimum required ECC of 4-bit correction per each 512 bytes.

I want to be able to use 1-bit ECC for the first partition where I
save the loader binary and has to be accessed by the ROM boot but use
a 4-bit ECC for my rootfs partition.

Does anyone have this same issue?

What is the best approach to store data in a NAND device using
different ECC techniques?

I've think of two approaches:

1- Adding an ioctl to mtdchar (something like ECCSETBITS) to change
the ECC technique used.
2- Use a platform data field to notify the omap2 nand driver that the
ROM boot only supports 1-bit ECC. So it can use a 1-bit ECC to write
and read the first 4 sectors but a 4-bit ECC for the rest.

Of course both approaches can only be used if the none of the nand
memory partitions are mounted.

Thank you and best regards,

--
Javier Martínez Canillas
(+34) 682 39 81 69
Barcelona, Spain

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