[PATCH v3 1/3] mtd: rawnand: rockchip-nand-controller: fix oobfree offset and description

[Johan Jonker <jbx6244@gmail.com>]

The MTD framework reserves 1 or 2 bytes for the bad block marker
depending on the bus size. The rockchip-nand-controller driver
currently only supports a 8 bit bus, but reserves standard 2 bytes
for the BBM in the chip->oob_poi buffer. The first free OOB byte is
therefore OOB2 at offset 2. Page Address (PA) bytes are located at the
last 4 positions before ECC. The current advertised free OOB area has
an offset that starts at OOB6 and a length that overlaps with the space
reserved for the PA bytes. Writing unrelated data to a reserved space
with a specific task can corrupt our boot block page read order.
Fix by changing the free OOB offset to 2.

This change breaks existing jffs2 users.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
---

Changed V3:
  Change prefixes
  Reword
  State break existing users.

---

Example:

Wrong free OOB offset starts at OOB6:
oob_region->offset = NFC_SYS_DATA_SIZE + 2;
                   = 4 + 2
                   = 6

oob_region->length = rknand->metadata_size - NFC_SYS_DATA_SIZE - 2;
                   = 32 - 4 - 2
                   = 26

Together with this length above it overlaps a reserved space for the
boot blocks Page Address(PA)

chip->oob_poi buffer layout for 8 steps:

BBM0   BBM1  OOB2  OOB3  | OOB4  OOB5  OOB6  OOB7

OOB8   OOB9  OOB10 OOB11 | OOB12 OOB13 OOB15 OOB15
OOB16  OOB17 OOB18 OOB19 | OOB20 OOB21 OOB22 OOB23

OOB24  OOB25 OOB26 OOB27 | PA0   PA1   PA2   PA3

ECC0   ECC1  ECC2  ECC3  | ...   ...   ...   ...

Fix by new offset at OOB2:
oob_region->offset = 2;

The full range of free OOB with 8 steps runs from OOB2
till/including OOB27.
---
 drivers/mtd/nand/raw/rockchip-nand-controller.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/mtd/nand/raw/rockchip-nand-controller.c b/drivers/mtd/nand/raw/rockchip-nand-controller.c
index 2312e2736..37fc07ba5 100644
--- a/drivers/mtd/nand/raw/rockchip-nand-controller.c
+++ b/drivers/mtd/nand/raw/rockchip-nand-controller.c
@@ -562,9 +562,10 @@ static int rk_nfc_write_page_raw(struct nand_chip *chip, const u8 *buf,
 		 *    BBM  OOB1 OOB2 OOB3 |......|  PA0  PA1  PA2  PA3
 		 *
 		 * The rk_nfc_ooblayout_free() function already has reserved
-		 * these 4 bytes with:
+		 * these 4 bytes together with 2 bytes for BBM
+		 * by reducing it's length:
 		 *
-		 * oob_region->offset = NFC_SYS_DATA_SIZE + 2;
+		 * oob_region->length = rknand->metadata_size - NFC_SYS_DATA_SIZE - 2;
 		 */
 		if (!i)
 			memcpy(rk_nfc_oob_ptr(chip, i),
@@ -933,12 +934,8 @@ static int rk_nfc_ooblayout_free(struct mtd_info *mtd, int section,
 	if (section)
 		return -ERANGE;

-	/*
-	 * The beginning of the OOB area stores the reserved data for the NFC,
-	 * the size of the reserved data is NFC_SYS_DATA_SIZE bytes.
-	 */
 	oob_region->length = rknand->metadata_size - NFC_SYS_DATA_SIZE - 2;
-	oob_region->offset = NFC_SYS_DATA_SIZE + 2;
+	oob_region->offset = 2;

 	return 0;
 }
--
2.30.2


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