[PATCH v3 00/52] mtd: rework ECC layout definition

On Thu, 25 Feb 2016 17:27:23 -0800
Stefan Agner [off-list ref] wrote:

Hi Boris,

On 2016-02-25 16:57, Boris Brezillon wrote:

quoted

Hello,

This patchset aims at getting rid of the nand_ecclayout limitations.
struct nand_ecclayout is defining fixed eccpos and oobfree arrays which
can only be increased by modifying the MTD_MAX_ECCPOS_ENTRIES_LARGE and
MTD_MAX_OOBFREE_ENTRIES_LARGE macros.
This approach forces us to modify the macro values each time we add a
new NAND chip with a bigger OOB area, and increasing these arrays also
penalize all platforms, even those who only support small NAND devices
(with small OOB area).

The idea to overcome this limitation, is to define the ECC/OOB layout
by the mean of two functions: ->ecc() and ->free(), which will
basically return the same information has those stored in the
nand_ecclayout struct.

Another advantage of this solution is that ECC layouts are usually
following a repetitive pattern (i.e. leave X bytes free and put Y bytes
of ECC per ECC chunk), which allows one to implement the ->ecc()
and ->free() functions with a simple logic that can be applied
to any size of OOB.

Patches 1 to 4 are just cleanups or trivial fixes that can be taken
independently.

Also note that the last two commits are removing the nand_ecclayout
definition, thus preventing any new driver to use this structure.
Of course, this step can be delayed if some of the previous patches
are not accepted.

Is the patch set somewhere available to pull from?

Yes, it's here [1].

Do I see things right that patch 21/52 contains the crucial function
nand_ooblayout_ecc_lp which calculate the ECC position? (for those who
do not provide mtd_ooblayout_ops anyway...)

You're correct. This implementation is here for NAND controller drivers
relying on the linux default ECC layout (the one used when soft ECC is
selected, or when not layout is specified). This layout is just putting
all ECC bytes at the end of the OOB area.

[1]https://github.com/bbrezillon/linux-0day/tree/nand/ecclayout

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com