[Buildroot] Writable EXT2 fs on dataflash (using MTD)

Ulf Samuelsson ulf at atmel.com
Mon Oct 15 16:14:49 UTC 2007

> You can make sure that the flash is unlocked by running:
> flash_unlock /dev/mtd/x
> (Where /dev/mtd/x is the character device corresponding to the mtd in
> question).
> "flash_unlock" is part of the mtd tools and can be selected under package
> selection in the buildroot.
> You might have better luck using jffs2 instead of ext2.  The jffs2 file
> system is intended for MTD devices, and uses "wear-leveling" to distribute
> writes over the entire flash part.

Luck has nothing to do with it...
using EXT2 will wear out the dataflash in record time...

There is some support for Dataflash in buildroot, but you have to set the
page size to 0x420 and the erase size to 0x2100.

The sizes are by default, the sizes needed for par flash.
If you make menuconfig and save it before changing this,
then the page/erase size will not be changed automagically,
and you file system will be built in the wrong way.

I am thinking of changing this to

config 4kB
config 1056 byte
config custom

config jffs_page_size_custom
    depends on custom

config jffs_page_size
    "0x1000" if 4kB
    "0x420" if 1056 byte
    $(jffs_page_size_custom) if custom

Then changing the choice, will update the value

and let the user supply

> Regards,
> Jon Nalley
> On 10/14/07, Jorge S. <jorgesolla at gmail.com> wrote:
>> Hi all,
>> I've created a rootfs for my AT91RM9200 based custom board and i'm unable
>> to mount the ext2 fs on a writable way.
>> I'm using an AT45DB64 spi dataflash as an MTD device and i've defined 3
>> partitions using this kernel bootargs:
>> console=/dev/ttyS0,115200 root=/dev/mtdblock2 
>> mtdparts=AT45DB642.spi0:168960(boot)ro,2162688(kernel),-(rootfs)rw
>> rootfstype=ext2 mem=32M
>> After booting the kernel always says:
>> VFS: Mounted root (ext2 filesystem) readonly.
>> Even if i try a "mount -o remount,rw /" from the busybox shell, i get 
>> this
>> message:
>> mount: /dev/root is write-protected, mounting read-only
>> The "rootfs" partition is defined "writable" at the u-boot code, so i
>> think i can assume the flash is Unlocked.
>> Any ideas? Did i miss something when building the Rootfs? any option?
>> Thanks in advance.

Best Regards
Ulf Samuelsson 

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