Hi Rick,

On Thursday 06 September 2007 14:30, Rick Bronson wrote:
> 
>   This is my first patch for yaffs2 so bear with me...  sorry if I missed
> something.
> 
> [PATCH] [YAFFS] YAFFS2: Add comments for maintaining backward compatibility.
> 
> [From: Rick Bronson <rick@efn.org>]
> [Acked-by: Realname <realmail>]
> Signed-off-by: Realname <realmail>
> 
> 
> diff -ruN yaffs2.orig/yaffs_mtdif1.c yaffs2/yaffs_mtdif1.c
> --- yaffs2.orig/yaffs_mtdif1.c	2007-07-23 12:14:04.000000000 -0700
> +++ yaffs2/yaffs_mtdif1.c	2007-09-06 11:26:13.000000000 -0700
> @@ -45,7 +45,8 @@
>  #endif
>  
>  #if 0
> -/* Use the following nand_ecclayout with MTD when using
> +/* Use the following nand ecclayout (replace the one in
> + * nand_base.c with this one) with MTD when using

Adding more comment/help describing how to use this nand_ecclayout is
good.  I would rather encourage folks to add this to their platform
"NAND probe routine" rather than the stock mtd/nand/nand_base.c
module.

>   * CONFIG_YAFFS_9BYTE_TAGS and the older on-NAND tags layout.
>   * If you have existing Yaffs images and the byte order differs from this,
>   * adjust 'oobfree' to match your existing Yaffs data.
> @@ -58,12 +59,24 @@
>   * We have/need PackedTags1 plus pageStatus: T0,T1,T2,T3,T4,T5,T6,T7,P
>   * where Tn are the tag bytes, En are MTD's ECC bytes, P is the pageStatus
>   * byte and B is the small-page bad-block indicator byte.
> + *
> + * If you need to maintain different OOB layouts on jffs2 vs yaffs on the
> + * same NAND part then you will need to set chip->ecc.layout on entry to
> + * the following routines: nand_read, nand_read_oob, nand_write,
> + * nand_write_oob, nand_erase_nand, nand_block_markbad.  You also need
> + * to set parts->ecclayout for the separate partitions, probably in your
> + * NAND probe routine.

Using different layouts for different partitions of a device is
not something that comes easy to MTD.  The layout being part of
the nand_chip object (single instance) rather that the mtd_partition
object. So I'm not sure I follow what you mean when you say "need to set
chip->ecc.layout on entry" -- do you mean make changes to nand_base.c
to support multiple (runtime) layouts?  If so, there's quite a bit
more to this, isn't there?

>   */
>  static struct nand_ecclayout nand_oob_16 = {
>  	.eccbytes = 6,
>  	.eccpos = { 8, 9, 10, 13, 14, 15 },
> +#ifdef CONFIG_YAFFS_9BYTE_TAGS
>  	.oobavail = 9,
>  	.oobfree = { { 0, 4 }, { 6, 2 }, { 11, 2 }, { 4, 1 } }
> +#else
> +	.oobavail = 8,
> +	.oobfree = { { 0, 4 }, { 6, 2 }, { 11, 2 } }
> +#endif
>  };
>  #endif

This ifdef only works if Yaffs config is part of the kernel build
because the file containing this data definition would normally be
in the (static) kernel or platform module -- not in Yaffs code.
If the layout were passed to MTD at initialization in the probe
routine, simply ifdef'ing the assignment to chip->ecc.layout in
the probe would be as easy. Also, what harm is there in offering
an additional byte of oob/spare if it's available?

-imcd