Spare area access information from JFFS2

Spare area access information from JFFS2

[Sudeep K N]

Hi,

       We are working on Nand Flash Controller which does not support
       ECC protection during Spare_Only Operation, rather it supports
       ECC protection for both Main_and_Spare area. In this regard,
       before to implement any workaround in my nand driver we want to
       know "Spare Area and Spare + Main area access sequence" from
       JFFS2 filesystem perspective during any JFFS2 operation.

       Proceeding further to observe JFFS2 Spare area access we found the
       the following:

       1. During Mount: scans the block, [erases], and writes "0x20031985"
               into the spare area on start of every block followed by another
               18 bytes which spans across multiple pages because free bytes in
               spare area is only 4
       2. Later during main page program operation our nand controller
               updates spare area ECC bytes, during this sequence we are not
               clear whether JFFS2 perform any spare operation to updates it
               meta data.
       3. Also, we want know, later the above sequence, does JFFS2 performs
               any spare only program operations.


Regards,
Sudeep

Re: Spare area access information from JFFS2

[Thomas Gleixner]

On Sat, 2007-05-05 at 21:48 +0530, Sudeep K N wrote:
>        1. During Mount: scans the block, [erases], and writes "0x20031985"
>                into the spare area on start of every block followed by another
>                18 bytes which spans across multiple pages because free bytes in
>                spare area is only 4

JFFS2 writes only 4 bytes, when you set the ecclayout information
correct. Even if you set it to something else, it writes max. 12 bytes.
So your 4 + 18 bytes observation is rather strange.

>        2. Later during main page program operation our nand controller
>                updates spare area ECC bytes, during this sequence we are not
>                clear whether JFFS2 perform any spare operation to updates it
>                meta data.

JFFS2 does not use the spare area for metadata information other than
the cleanmarker.

>        3. Also, we want know, later the above sequence, does JFFS2 performs
>                any spare only program operations.
> 

No. The only exception is the block_mark_bad operation.

	tglx