Re: mxc nand i.mx35: no OOB with HW_ECC

[Sascha Hauer <s.hauer@pengutronix.de>]

Hi John,

On Tue, Nov 03, 2009 at 04:25:10PM +0100, John Ogness wrote:
> Hi,
> 
> I spent a while trying to figure out why JFFS2 was getting hardware ECC
> errors on an i.MX35 NANDFC with 2K pages. The problem also existed when
> using nandwrite together with the -n and -o options.
> 
> The problem is that for page sizes larger than 512 bytes, the i.MX35
> NANDFC can only write the page and oob data together. When writing the
> page and oob data, the ECC hardware also writes the ECC codes for
> it. This is ok if the filesystem driver or userspace application
> understands that only one write per page+oob is allowed.
> 
> But jffs2 and "nandwrite -n -o" assume that they can write the oob data
> and the page data separately. With the recently posted mxc_nand.c
> driver, this results in the NANDFC writing the ECC codes to flash
> twice... with different values. This means the ECC codes that end up on
> the flash chip are garbage.

I can confirm jffs2 errors on i.MX35 with the patches I posted. And yes
you're right, I mostly use UBIFS.

Freescale originally provided two drivers, one for the i.MX27/31 type
nand controller (v1) from which the in kernel driver is derived and one
for the remaining nand controllers (i.mx35/25) (v2). What I did is to
work on both drivers till they both looked (nearly) the same and posted
the patches for the v1 driver.

One remaining difference is in mxc_do_addr_cycle(). Here is the version
from the v2 driver which works with jffs2:

static void mxc_do_addr_cycle(struct mtd_info *mtd, int column, int
page_addr)
{
	struct nand_chip *nand_chip = mtd->priv;
	struct mxc_nand_host *host = nand_chip->priv;

	u32 page_mask = nand_chip->pagemask;

	if (column != -1) {
		send_addr(host, column & 0xFF, 0);
		if (mtd->writesize == 2048) {
			/* another col addr cycle for 2k page */
			send_addr(host, (column >> 8) & 0xF, 0);
		} else if (mtd->writesize == 4096) {
			/* another col addr cycle for 4k page */
			send_addr(host, (column >> 8) & 0x1F, 0);
		}
	}
	if (page_addr != -1) {
		do {
			send_addr(host, (page_addr & 0xff), 0);
			page_mask >>= 8;
			page_addr >>= 8;
		} while (page_mask != 0);
	}
}

Putting this function into the v1 driver makes the driver work for me on
i.MX35 with jffs2. Can you confirm this?

I haven't looked deeply into the differences and I suspect this version
of mxc_do_addr_cycle() won't work on the v1 type controllers, so this is
not a solution yet.

Sascha

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