Erase verify problem with OneNAND

[Jarkko Lavinen <jarkko.lavinen@nokia.com>]

Hi Kyungmin

I have a strange erase verify read problem with OneNand. It occurs
strangely when crossing the 128MB border, first erasing (and
presumably verifying) a block on other side and then erasing another
block on the other side. Then verify reads garbage.

I am using CVS head for the drivers/mtd but the JFFS2 part is from the
2.6.15 kernel, before Erase Block Headers were committed. Onenand_base.c
is rev 1.15. The test board has muxed 256MB OneNand.

I see JFFS2 repeatably complaining "Newly-erased block contained
word...".  This comes from fs/jffs2/erase.c:jffs2_block_check_erase()
which reads the erased block and checks all the bits are 1.

I see this occuring when I flash JFFS2 root image and boot it. Our
bootloader leaves unused erase blocks empty, without cleanmarker.
When JFFS2 sees an empty block, it has to erase it again since there 
is no cleanmarker. After erasing, it reads the first page to see it 
really is empty.

For some reason the first verify read at physical offset 0x7fe0000 
(JFFS2 report offset 0x07b60000 relative to the partition offset 
0x480000) fails but retry succeeds -- which means the block was 
correctly erased but the first verify reads some garbage.

This is tricky to debug, since the problem disappears if I increase 
MTD debug level. On the other hand the verify problem seems to appear
always after after flashing and booting the board.

I have modified jffs2_block_check_erase() to retry the verify read
if garbage is seen at the erased page.  I am using MTD debug level
0 and changed onenand_erase to report at that level to see when it 
is being called.

The repeatably occuring one:

  ...
  onenand_erase: start = 0x08040000, len = 131072
  onenand_erase: start = 0x08020000, len = 131072
  onenand_erase: start = 0x08000000, len = 131072
  onenand_erase: start = 0x07fe0000, len = 131072
  Newly-erased block contained word 0x45e0f628 at offset 0x07b60000
  Read OK after 1 retries
  onenand_erase: start = 0x07fc0000, len = 131072
  onenand_erase: start = 0x07fa0000, len = 131072
  onenand_erase: start = 0x07f80000, len = 131072
  ...

Another exmaple, less frequent:

  onenand_erase: start = 0x04ce0000, len = 131072
  onenand_erase: start = 0x04cc0000, len = 131072
  onenand_erase: start = 0x04ca0000, len = 131072
  onenand_erase: start = 0x0ffe0000, len = 131072
  Newly-erased block contained word 0x7ea4c at offset 0x0fb60000
  Read OK after 1 retries

Jarkko Lavinen