realtek: mtd: nand: backport realtek-ecc OOB check fix patch

Add a backport patch of realtek ecc driver which has been accepted
upstream. It enables us to make use of devices with NAND that have
OOB size larger than 64 and utilize Realtek ECC engine in OpenWrt.

Signed-off-by: Rustam Adilov <adilov@tutamail.com>
Link: https://github.com/openwrt/openwrt/pull/22243
Signed-off-by: Robert Marko <robimarko@gmail.com>

diff --git a/target/linux/realtek/patches-6.12/022-v7.0-mtd-nand-realtek-ecc-relax-OOB-size-check-to-minimum.patch b/target/linux/realtek/patches-6.12/022-v7.0-mtd-nand-realtek-ecc-relax-OOB-size-check-to-minimum.patch
new file mode 100644 (file)
index 0000000..8155c78
--- /dev/null
+++ b/target/linux/realtek/patches-6.12/022-v7.0-mtd-nand-realtek-ecc-relax-OOB-size-check-to-minimum.patch
@@ -0,0 +1,67 @@
+From 0c741b8b6963e584b41c284cd743c545636edb04 Mon Sep 17 00:00:00 2001
+From: Ahmed Naseef <naseefkm@gmail.com>
+Date: Sat, 7 Feb 2026 11:02:43 +0400
+Subject: 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>
+---
+ drivers/mtd/nand/ecc-realtek.c | 18 ++++++++++--------
+ 1 file changed, 10 insertions(+), 8 deletions(-)
+
+--- a/drivers/mtd/nand/ecc-realtek.c
++++ b/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
+       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;
+       }
+