Re: [PATCH 1/2] mtd: nand: add OOB argument to NAND {read, write}_page interfaces

[Shmulik Ladkani <shmulik.ladkani@gmail.com>]

Hi Bastian,

On Mon, 23 Apr 2012 11:14:39 +0200 Bastian Hecht <hechtb@googlemail.com> wrote:
> Following this thread, I wondered how mtd_write_oob is meant to work.
> The sh_flctl code simply writes the OOB data 1 to 1 into the oob area
> of the nand chip when using hardware ECC. So when reading this, it
> should result in a corrupted page. Is the driver meant to OR the ECC
> code to the buffer? Then the driver would need a page read and write
> it back applying the oob data, no?

The beahvior is dependent on mtd_oob_ops->mode.

If mode is MTD_OPS_AUTO_OOB, 'nand_fill_oob' places the user provided
'oobbuf' into the "free" locations within the OOB layout (as defined by
'chip->ecc.layout->oobfree').
Implementor of 'chip->ecc.write_page' is expected to take care of ECC
caclulation and fill the ECC bytes (driver's or HW responsibility).

If the mode is MTD_OPS_RAW, user provided 'oobbuf' should be transferred
as-is, without error correction ('chip->ecc.write_page_raw' will be
invoked).

If the mode is MTD_OPS_PLACE_OOB, then 'nand_fill_oob' copies user's
'oobbuf' onto 'oob_poi'.
As with MTD_OPS_AUTO_OOB, implementor of 'chip->ecc.write_page' is
expected to take care of ECC calculation; the ECC locations are assumed
to be overwritten (ignoring user's bytes at the ECC locations).

This is according to the nand_base.c default methods.
For example, you can follow nand_do_write_ops, nand_write_page,
nand_write_page_swecc.

Regards,
Shmulik