imx-bbu-nand-fcb: Workaround ROM checking fingerprint before correcting bitflips

The FCB block is protected with a ECC code which can correct 1bit errors
and detect 2bit errors. This works fine for all fields except the
fingerprint marker (Containing "FCB") and the version field. Here the ROM
chooses to check the correct value of the fields *before* running the ECC
correction. Thus a FCB is not used by the ROM anymore when it has a bitflip
in the fingerprint or version. For us this means we have to rewrite the FCB
in this case, so reject the faulty FCB in read_fcb_hamming_13_8() which
triggers a rewrite during the check operation.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 11 insertions, 0 deletions

diff --git a/common/imx-bbu-nand-fcb.c b/common/imx-bbu-nand-fcb.c
index 15ddf5d7b0..8842ba6c58 100644
--- a/common/imx-bbu-nand-fcb.c
+++ b/common/imx-bbu-nand-fcb.c
@@ -318,6 +318,17 @@ struct fcb_block *read_fcb_hamming_13_8(void *rawpage)
 	fcb = rawpage + 12;
 	ecc = rawpage + 512 + 12;
 
+	/*
+	 * The ROM does the check for the correct fingerprint and version before
+	 * correcting bitflips. This means we cannot allow bitflips in the
+	 * fingerprint and version. We bail out with an error if it's not correct.
+	 * This is currently done in the i.MX6qdl path. It needs to be checked if
+	 * the same happens in the BCH encoded variants (i.MX6ul(l)) aswell.
+	 */
+	if (((struct fcb_block *)fcb)->FingerPrint != 0x20424346 ||
+	    ((struct fcb_block *)fcb)->Version != 0x01000000)
+		return ERR_PTR(-EINVAL);
+
 	for (i = 0; i < 512; i++) {
 		parity = ecc[i];
 		np = calculate_parity_13_8(fcb[i]);