[PATCH v4 2/5] mtd: rawnand: nand_base: Handle algorithm selection

[Linus Walleij]

For BRCMNAND with 1-bit BCH ECC (BCH-1) such as used on the
D-Link DIR-885L and DIR-890L routers, we need to explicitly
select the ECC like this in the device tree:

  nand-ecc-algo = "bch";
  nand-ecc-strength = <1>;
  nand-ecc-step-size = <512>;

This is handled by the Linux kernel but U-Boot core does
not respect this. Fix it up by parsing the algorithm and
preserve the behaviour using this property to select
software BCH as far as possible.

Reviewed-by: Michael Trimarchi <michael at amarulasolutions.com>
Acked-by: William Zhang <william.zhang at broadcom.com>
Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
---
ChangeLog v3->v4:
- After a bug report from Tom, be more careful when
  assigning algorithm: only overwrite the chip default when
  something other than undefined was actually detected.
ChangeLog v2->v3:
- Collect review tags from Michael and William
- Resend with the NorthStar enablement patches
ChangeLog v1->v2:
- Drop pointless check for ecc_algo >= 0, it is always
  >= 0.
---
 drivers/mtd/nand/raw/nand_base.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
index 9eba360d55f3..6b4adcf6bdc9 100644
--- a/drivers/mtd/nand/raw/nand_base.c
+++ b/drivers/mtd/nand/raw/nand_base.c
@@ -4487,6 +4487,7 @@ EXPORT_SYMBOL(nand_detect);
 static int nand_dt_init(struct mtd_info *mtd, struct nand_chip *chip, ofnode node)
 {
 	int ret, ecc_mode = -1, ecc_strength, ecc_step;
+	int ecc_algo = NAND_ECC_UNKNOWN;
 	const char *str;
 
 	ret = ofnode_read_s32_default(node, "nand-bus-width", -1);
@@ -4512,10 +4513,22 @@ static int nand_dt_init(struct mtd_info *mtd, struct nand_chip *chip, ofnode nod
 			ecc_mode = NAND_ECC_SOFT_BCH;
 	}
 
-	if (ecc_mode == NAND_ECC_SOFT) {
-		str = ofnode_read_string(node, "nand-ecc-algo");
-		if (str && !strcmp(str, "bch"))
-			ecc_mode = NAND_ECC_SOFT_BCH;
+	str = ofnode_read_string(node, "nand-ecc-algo");
+	if (str) {
+		/*
+		 * If we are in NAND_ECC_SOFT mode, just alter the
+		 * soft mode to BCH here. No change of algorithm.
+		 */
+		if (ecc_mode == NAND_ECC_SOFT) {
+			if (!strcmp(str, "bch"))
+				ecc_mode = NAND_ECC_SOFT_BCH;
+		} else {
+			if (!strcmp(str, "bch")) {
+				ecc_algo = NAND_ECC_BCH;
+			} else if (!strcmp(str, "hamming")) {
+				ecc_algo = NAND_ECC_HAMMING;
+			}
+		}
 	}
 
 	ecc_strength = ofnode_read_s32_default(node,
@@ -4529,6 +4542,14 @@ static int nand_dt_init(struct mtd_info *mtd, struct nand_chip *chip, ofnode nod
 		return -EINVAL;
 	}
 
+	/*
+	 * Chip drivers may have assigned default algorithms here,
+	 * onlt override it if we have found something explicitly
+	 * specified in the device tree.
+	 */
+	if (ecc_algo != NAND_ECC_UNKNOWN)
+		chip->ecc.algo = ecc_algo;
+
 	if (ecc_mode >= 0)
 		chip->ecc.mode = ecc_mode;
 
-- 
2.39.2