Hi Avinash,
Hi Peter,

On 23.11.2012 11:43, Philip, Avinash wrote:

On Wed, Nov 21, 2012 at 15:45:23, Daniel Mack wrote:

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On 20.11.2012 16:59, Peter Korsgaard wrote:

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"Daniel" == Daniel Mack [off-list ref] writes:

Peter,

In patch [1], mtd: nand: omap2: Support for hardware BCH

ecc_layout made compatible with Rom Boot Loader ECC layout for am335x.

This action is based on is_elm_used flag.

Requirement of this flag is to identify the whether the platform
ELM module & based on this configure ELM module if present.

But ideally BCH8 ecc lay out didn't have a dependency on ELM, it
can work with software BCH ecc. RBL compatibility is missing
in software BCH because of addition of constant polynomial to
ecc vector. If we remove the dependency on erased page handling
by ecc vector with constant polynomial, software BCH can do the
job of RBL compatibility.

Ivan,
Do you have any suggestions?
Discussion for RBL compatibility found at [2].

It is good that software BCH also support RBL compatibility by suppressing
constant polynomial modification. Then ecc layout can be selected from
DT entry and error correction can be chosen between software/hardware
depending on the availability of ELM hardware.
Currently RBL BCH8 compatibility depends on the availability of ELM
hardware. Later once software BCH start supporting RBL compatibility,
we can remove  the check.

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That is what I experienced, yes. The kernel was unable to parse NAND
pages that were written from U-Boot with bch8 hardware mode when the elm
module was not active. Maybe someone from TI can explain that? Giving it
a dedicated name would also solve the problem with the extra DT property.

Daniel,

Currently BCH8 is supported with software ecc error correction in mainline.
The layout for BCH8 ECC layout is
0-1 -> BAD block markers
2-11-> oob free area
12-63-> BCH8 ECC.

RBL ECC layout is
0-1 -> BAD block markers
2-57-> BCH8 ecc layout
58-63-> OOB free area

As u-boot also maintain RBL ecc layout, write from U-boot
and read from Linux requires compatibility with RBL ecc layout.
The same is achieved in the patch [1], with by setting is_elm_used
to true.

1. https://lkml.org/lkml/2012/10/31/87
2. https://lkml.org/lkml/2012/10/11/20

So, after reading this, I'm still uncertain what's your preferred way of
handling the bindings here. Are you saying we should stick with the
is_elm_used flag, and subsequently care for BCH8 software mode
compatibility?

I would like to submit a new version soon, so it can be queued up for
the next merge window, and that decision is the last blocker currently
for sending out a new series.


Many thanks,
Daniel