u-boot how to mark bad blocks

Question

While in U-boot in an arm based board (wb45n), I manually erase and then mark a block bad.

U-Boot> nand erase 0x00720000 20000

NAND erase: device 0 offset 0x00720000, size 0x20000
Erasing at 0x720000 -- 100% complete.
OK
U-Boot> nand markbad 0x00720000
block 0x00720000 successfully marked as bad
U-Boot> nand bad
>
Device 0 bad blocks:
00720000

I write software and can see the bad blocks being skipped in the process.

NAND write: device 0 offset 0x5e0000, size 0x16c0000
Skip bad block 0x00720000
23855104 bytes written: OK

After the software writing, I reboot and the bad blocks are not there.

U-Boot> nand bad
>
Device 0 bad blocks:
U-Boot>

Seems as if they have been automatically corrected. If I don't erase the blocks before marking them bad, I can write software successfully but I (often but not always) get the following error during the kernel boot: (I don' t really know why this error message is produced, any explanations are welcome)

UBI error: scan_peb: bad image sequence number 1748114077 in PEB 175, expected 1578922167

Erase counter header dump:

    magic          0x55424923
    version        1
    ec             1
    vid_hdr_offset 2048
    data_offset    4096
    image_seq      1748114077
    hdr_crc        0x285278f

Starting kernel ...

Uncompressing Linux... done, booting the kernel.

add to erase: PEB 0, EC 0 UBI error: ubi_compare_lebs: unsupported on-flash UBI format
UBI error: ubi_attach_mtd_dev: failed to attach mtd6, error -22
UBI error: ubi_init: cannot attach mtd6
UBIFS error (pid 1): ubifs_mount: cannot open "ubi0:rootfs", error -19
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown- block(0,0)

What I am trying to do is test the board to see how many bad blocks it can handle before failing.

Is the way I mark the bad blocks correct?
Why do the bad blocks disappear?
Is there a way to mark bad blocks that will persist?
What does the last error mean?

Answer 1

https://community.nxp.com/thread/334536#comment-453692

the error is related to a problem in the flashing of the board, that is:

1. you flash a new image incorrectly - you do not erase whole flash

2. you flash a new image - by erasing only the erase blocks where you write, but not erasing the rest of eraseblock.

I can imagine this happening if

• you omitted your nand erase or
• you wrote an image with N blocks marked bad on the NAND, then subsequently wrote the same image but with N-1 blocks marked bad on the NAND. After the end of the current image, there would be 1 block left over at the end from the previous image, which would not have been overwritten.