mtd: nand: realtek-ecc: relax OOB size check to minimum

The ECC engine strictly validates that flash OOB size equals exactly
64 bytes. However, some NAND chips have a larger physical OOB while
vendor firmware only uses the first 64 bytes for the ECC layout. For
example the Macronix MX35LF1G24AD found in the Netlink HG323DAC has
128 byte physical OOB but vendor firmware only uses the first 64
bytes (24 bytes free + 40 bytes BCH6 parity), leaving bytes 64-127
unused.

Since the engine only operates on the first 64 bytes of OOB
regardless of the physical size, change the check from exact match
to minimum size. Flash with OOB >= 64 bytes works correctly with
the engine's 64-byte layout.

Suggested-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Signed-off-by: Ahmed Naseef <naseefkm@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

Author: naseef

drivers/mtd/nand/ecc-realtek.c

@@ -17,10 +17,12 @@
  * - BCH12 : Generate 20 ECC bytes from 512 data bytes plus 6 free bytes
  *
  * It can run for arbitrary NAND flash chips with different block and OOB sizes. Currently there
- * are only two known devices in the wild that have NAND flash and make use of this ECC engine
- * (Linksys LGS328C & LGS352C). To keep compatibility with vendor firmware, new modes can only
- * be added when new data layouts have been analyzed. For now allow BCH6 on flash with 2048 byte
- * blocks and 64 bytes oob.
+ * are a few known devices in the wild that make use of this ECC engine
+ * (Linksys LGS328C, LGS352C & Netlink HG323DAC). To keep compatibility with vendor firmware,
+ * new modes can only be added when new data layouts have been analyzed. For now allow BCH6 on
+ * flash with 2048 byte blocks and at least 64 bytes oob. Some vendors make use of
+ * 128 bytes OOB NAND chips (e.g. Macronix MX35LF1G24AD) but only use BCH6 and thus the first
+ * 64 bytes of the OOB area. In this case the engine leaves any extra bytes unused.
  *
  * This driver aligns with kernel ECC naming conventions. Neverthless a short notice on the
  * Realtek naming conventions for the different structures in the OOB area.
@@ -39,7 +41,7 @@
  */
 
 #define RTL_ECC_ALLOWED_PAGE_SIZE 	2048
-#define RTL_ECC_ALLOWED_OOB_SIZE	64
+#define RTL_ECC_ALLOWED_MIN_OOB_SIZE	64
 #define RTL_ECC_ALLOWED_STRENGTH	6
 
 #define RTL_ECC_BLOCK_SIZE 		512
@@ -310,10 +312,10 @@ static int rtl_ecc_check_support(struct nand_device *nand)
 	struct mtd_info *mtd = nanddev_to_mtd(nand);
 	struct device *dev = nand->ecc.engine->dev;
 
-	if (mtd->oobsize != RTL_ECC_ALLOWED_OOB_SIZE ||
+	if (mtd->oobsize < RTL_ECC_ALLOWED_MIN_OOB_SIZE ||
 	    mtd->writesize != RTL_ECC_ALLOWED_PAGE_SIZE) {
-		dev_err(dev, "only flash geometry data=%d, oob=%d supported\n",
-			RTL_ECC_ALLOWED_PAGE_SIZE, RTL_ECC_ALLOWED_OOB_SIZE);
+		dev_err(dev, "only flash geometry data=%d, oob>=%d supported\n",
+			RTL_ECC_ALLOWED_PAGE_SIZE, RTL_ECC_ALLOWED_MIN_OOB_SIZE);
 		return -EINVAL;
 	}