[OpenWrt-Users] How to use JFFS based firmware ?

[FrekoDing]

Hi,

I've just build a custom firmware for my Asus WL500gp (V1 Atheros Wifi).
I choose to use a JFFS2 root filesystem by setting my conf like that 
(only JFFS) :

# CONFIG_TARGET_ROOTFS_INITRAMFS is not set
CONFIG_TARGET_ROOTFS_JFFS2=y
# CONFIG_TARGET_ROOTFS_SQUASHFS is not set
# CONFIG_TARGET_ROOTFS_TGZ is not set
# CONFIG_TARGET_ROOTFS_CPIOGZ is not set
# CONFIG_TARGET_ROOTFS_EXT2FS is not set

Is it good ?
Why this question ?
The built result take me 2 files : openwrt-brcm47xx-jffs2-128k.trx and 
openwrt-brcm47xx-jffs2-64k.trx.
The openwrt documentation specify that use the first file for 8 MB flash 
version and the second for 4 MB flash version.
I checked on the hardware table (http://wiki.openwrt.org/OpenWrtDocs/Har 
... us/WL500GP)
I've to use the 128k version... the router don't boot with it.
It boot only with the 64k version.
I've forget something somewhere ?

To help, the df -h result :

root at OpenWrt:/# df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/mtdblock2            6.9M      2.3M      4.6M  33% /
tmpfs                    14.7M     40.0k     14.6M   0% /tmp
tmpfs                   512.0k         0    512.0k   0% /dev

Last question : how to know the embedded flash real size ?

Many thanks for your help !