[PATCH 0/2] mtd: rawnand: vf610_nfc: two fixes for chips with large OOB and for erased pages

[Mehmet Fide]

From: Mehmet Fide <mehmet.fide at screeningeagle.com>

Two independent fixes for the Vybrid NAND flash controller, both found
while bringing a Colibri VF61 up on mainline and both verified on
hardware.

Patch 1 is a regression. The driver clamps mtd->oobsize to the 64 bytes
its ECC layout uses, but since commit a7ab085d7c16 ("mtd: rawnand:
Initialize the nand_device object") nand_scan_tail() restores the value
from the memory organization right after ->attach_chip(), so the clamp
is silently lost. On a chip with more than 64 bytes of OOB every
ECC-protected read then fails and the board does not boot. Clamping the
memory organization as well is what the rest of the tree does when a
driver has to change the OOB size (nand_samsung.c, nand_onfi.c,
nand_jedec.c and denali.c all write memorg->oobsize); mpc5121_nfc.c
touches mtd->oobsize directly but does so before nand_scan(), so it is
not affected.

Doing this in ->attach_chip() is deliberate: the chip really does have
112 spare bytes, it is this controller that can only use 64, and
->attach_chip() is where a controller adapts to the detected chip. The
patch also touches the memory organization because nanddev_init(), which
runs later in nand_scan_tail(), re-derives mtd->{erasesize, writesize,
writebufsize, oobsize, size} from it, so an adjustment made only in mtd
does not survive. If you would rather have the core preserve what
->attach_chip() set up, or a dedicated way for a driver to declare that
it uses fewer OOB bytes than the chip provides, I am happy to respin; I
went with the minimal form because this is a regression fix that should
be backportable.

Patch 2 makes the erased-page check look at the flash instead of at the
controller buffer. When the ECC engine fails to decode a page it leaves
a bogus single-bit "correction" in that buffer, which the check counts
as a real bitflip; on the 60-byte ECC mode every erased page is
reported with one corrected bitflip, which renders the MTD statistics
useless for flash health monitoring.

Testing, all booting from NAND on an Iris carrier with Linux 6.18.44 and
U-Boot 2026.07:

  0010 Colibri VF50 128MB V1.2A     Macronix MX30LF1G08AA, 64-byte OOB
  0013 Colibri VF50 128MB IT V1.2B  Macronix MX30LF1G18AC, 64-byte OOB
  0012 Colibri VF61 256MB IT V1.2B  Macronix MX30LF4G28AC, 112-byte OOB

Without patch 1 the VF61 cannot attach UBI at all. With the series all
three boot, mtd oobsize stays 64, the bad block table written by an
older kernel reads back without ECC errors and the corrected-bitflip
counter stays at zero over a full-partition nanddump. The clamp only
triggers on the VF61 chip, so both patches are a no-op on the two VF50
revisions, which is what I wanted to confirm before sending them.

The credit for spotting both problems goes to Edward Karpicz, who
reported them on the Toradex community forum.

Mehmet Fide (2):
  mtd: rawnand: vf610_nfc: fix reads on chips with more than 64 bytes of
    OOB
  mtd: rawnand: vf610_nfc: fix false bitflips on reads of erased pages

 drivers/mtd/nand/raw/vf610_nfc.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)


base-commit: 15a3cbce32994141252bb4ecfe3ff3a5d22d0b4f
-- 
2.54.0