[PATCH] mtd: rawnand: nand_bbt: Skip bad blocks when searching for the BBT in NAND

[Stefan Riedmueller]

The blocks containing the bad block table can become bad as well. So
make sure to skip any blocks that are marked bad when searching for the
bad block table.

Otherwise in very rare cases where two BBT blocks wear out it might
happen that an obsolete BBT is used instead of a newer available
version.

This only applies to drivers which make use of a bad block marker in flash.
Other drivers won't be able to identify bad BBT blocks and thus can't skip
these.

Signed-off-by: Stefan Riedmueller <s.riedmueller@xxxxxxxxx>
---

Hi,

this is the second approach of this patch. The first one [1] unfortunately lead
to boot failures on i.MX 27 boards [2] since the i.MX 27 driver uses the bad
block marker position for the bad block table marker which lead to falsely
identifying all BBT blocks as bad.

This new patch now skips the check for bad BBT blocks if the BBT marker
position in OOB overlaps with the bad block marker position or if a driver
can't use bad block markers in flash at all (NAND_BBT_NO_OOB_BBM or
NAND_NO_BBM_QUIRK are set). This hopefully makes sure we don't break drivers
which cannot check for bad BBT blocks due to the limitations mentioned before.

I was only able to test this patch on a phyCORE-i.MX 6 and a phyCARD-i.MX 27.
Therfore would really appreciate more people testing this to make sure I have
not missed another use case where the bad block marker position in OOB is used
in a different way than for the BBM.

Regards,
Stefan

[1] https://lore.kernel.org/linux-mtd/20210325102337.481172-1-s.riedmueller@xxxxxxxxx/
[2] https://lore.kernel.org/linux-mtd/CAOMZO5DufVR=+EzCa1-MPUc+ZefZVTXb5Kgu3Wxms7cxw9GmGg@xxxxxxxxxxxxxx/

 drivers/mtd/nand/raw/nand_bbt.c | 34 +++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/drivers/mtd/nand/raw/nand_bbt.c b/drivers/mtd/nand/raw/nand_bbt.c
index dced32a126d9..2a30714350ee 100644
--- a/drivers/mtd/nand/raw/nand_bbt.c
+++ b/drivers/mtd/nand/raw/nand_bbt.c
@@ -447,6 +447,36 @@ static int scan_block_fast(struct nand_chip *this, struct nand_bbt_descr *bd,
 	return 0;
 }
 
+/* Check if a potential BBT block is marked as bad */
+static int bbt_block_checkbad(struct nand_chip *this,
+				      struct nand_bbt_descr *td,
+				      loff_t offs, uint8_t *buf)
+{
+	struct nand_bbt_descr *bd = this->badblock_pattern;
+
+	/*
+	 * No need to check for a bad BBT block if the BBM area overlaps with
+	 * the bad block table marker area in OOB since writing a BBM here
+	 * invalidates the bad block table marker anyway.
+	 */
+	if (!(td->options & NAND_BBT_NO_OOB) &&
+	    td->offs >= bd->offs && td->offs < bd->offs + bd->len)
+		return 0;
+
+	/*
+	 * There is no point in checking for a bad block marker if writing
+	 * such marker is not supported
+	 */
+	if (this->bbt_options & NAND_BBT_NO_OOB_BBM ||
+	    this->options & NAND_NO_BBM_QUIRK)
+		return 0;
+
+	if (scan_block_fast(this, bd, offs, buf) > 0)
+		return 1;
+
+	return 0;
+}
+
 /**
  * create_bbt - [GENERIC] Create a bad block table by scanning the device
  * @this: NAND chip object
@@ -560,6 +590,10 @@ static int search_bbt(struct nand_chip *this, uint8_t *buf,
 			int actblock = startblock + dir * block;
 			loff_t offs = (loff_t)actblock << this->bbt_erase_shift;
 
+			/* Check if block is marked bad */
+			if (bbt_block_checkbad(this, td, offs, buf))
+				continue;
+
 			/* Read first page */
 			scan_read(this, buf, offs, mtd->writesize, td);
 			if (!check_pattern(buf, scanlen, mtd->writesize, td)) {
-- 
2.25.1