Re: [LINUX PATCH v17 1/2] mtd: rawnand: nand_micron: Do not over write driver's read_page()/write_page()

[Helmut Grohne]

On Tue, Jun 25, 2019 at 06:46:29AM +0200, Naga Sureshkumar Relli wrote:
> --- a/drivers/mtd/nand/raw/nand_micron.c
> +++ b/drivers/mtd/nand/raw/nand_micron.c
> @@ -500,8 +500,11 @@ static int micron_nand_init(struct nand_chip *chip)
>  		chip->ecc.size = 512;
>  		chip->ecc.strength = chip->base.eccreq.strength;
>  		chip->ecc.algo = NAND_ECC_BCH;
> -		chip->ecc.read_page = micron_nand_read_page_on_die_ecc;
> -		chip->ecc.write_page = micron_nand_write_page_on_die_ecc;
> +		if (!chip->ecc.read_page)
> +			chip->ecc.read_page = micron_nand_read_page_on_die_ecc;
> +
> +		if (!chip->ecc.write_page)
> +			chip->ecc.write_page = micron_nand_write_page_on_die_ecc;

When used with pl353_nand.c, this change prioritizes the
pl353_nand_read_page_raw/pl353_nand_write_page_raw implementations over
micron_nand_read_page_on_die_ecc/micron_nand_write_page_on_die_ecc. The
pl353 implementations don't check the status register of the flash for
NAND_ECC_STATUS_WRITE_RECOMMENDED nor do they update ecc_stats.failed in
any way. Unless I am mistaken, this implies that bitflips cannot be
detected at all anymore.

However, this is the change that makes a MT29F2G08ABAEAWP practically
work with jffs2 on the Zynq platform.

In this context, I countered a document from Micron[1] indicating that
their on-die chips are incompatible with jffs2 as is, because the on-die
oob layout is incompatible with jffs2. I suppose that using the raw
variants puts jffs2 in full control of the oob area, but is this really
the correct solution?

Helmut

[1] https://www.micron.com/~/media/Documents/Products/Technical%20Note/NAND%20Flash/tn2975_enable_on-die-ECC_NAND_JFFS2.pdf