[PATCH 18/20] mtd: nand: ecc-hamming: Let the software Hamming ECC engine be unselected

[Miquel Raynal]

There is no reason to always embed the software Hamming ECC engine
implementation. By default it is (with raw NAND), but we can let the
user decide.

Signed-off-by: Miquel Raynal <miquel.raynal at bootlin.com>
---
 drivers/mtd/nand/Kconfig                | 11 +++++++-
 drivers/mtd/nand/raw/Kconfig            |  2 +-
 include/linux/mtd/nand-ecc-sw-hamming.h | 36 +++++++++++++++++++++++++
 3 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/nand/Kconfig b/drivers/mtd/nand/Kconfig
index 306c33ca3448..15ffe1a1b863 100644
--- a/drivers/mtd/nand/Kconfig
+++ b/drivers/mtd/nand/Kconfig
@@ -16,7 +16,16 @@ config MTD_NAND_ECC
        depends on MTD_NAND_CORE
 
 config MTD_NAND_ECC_SW_HAMMING
-	bool
+	bool "Software Hamming ECC engine"
+	default y if MTD_RAW_NAND
+	select MTD_NAND_ECC
+	help
+	  This enables support for software Hamming error
+	  correction. This correction can correct up to 1 bit error
+	  per chunk and detect up to 2 bit errors. While it used to be
+	  widely used with old parts, newer NAND chips usually require
+	  more strength correction and in this case BCH or RS will be
+	  preferred.
 
 config MTD_NAND_ECC_SW_HAMMING_SMC
 	bool "NAND ECC Smart Media byte order"
diff --git a/drivers/mtd/nand/raw/Kconfig b/drivers/mtd/nand/raw/Kconfig
index 6149096e32cb..cc86d6e4e042 100644
--- a/drivers/mtd/nand/raw/Kconfig
+++ b/drivers/mtd/nand/raw/Kconfig
@@ -3,7 +3,6 @@ menuconfig MTD_RAW_NAND
 	tristate "Raw/Parallel NAND Device Support"
 	select MTD_NAND_CORE
 	select MTD_NAND_ECC
-	select MTD_NAND_ECC_SW_HAMMING
 	help
 	  This enables support for accessing all type of raw/parallel
 	  NAND flash devices. For further information see
@@ -72,6 +71,7 @@ config MTD_NAND_AU1550
 config MTD_NAND_NDFC
 	tristate "IBM/MCC 4xx NAND controller"
 	depends on 4xx
+	select MTD_NAND_ECC_SW_HAMMING
 	select MTD_NAND_ECC_SW_HAMMING_SMC
 	help
 	  NDFC Nand Flash Controllers are integrated in IBM/AMCC's 4xx SoCs
diff --git a/include/linux/mtd/nand-ecc-sw-hamming.h b/include/linux/mtd/nand-ecc-sw-hamming.h
index 9d4b4d623741..5a39e96c3546 100644
--- a/include/linux/mtd/nand-ecc-sw-hamming.h
+++ b/include/linux/mtd/nand-ecc-sw-hamming.h
@@ -32,6 +32,8 @@ struct nand_ecc_sw_hamming_conf {
 	unsigned int sm_order;
 };
 
+#if IS_ENABLED(CONFIG_MTD_NAND_ECC_SW_HAMMING)
+
 int ecc_sw_hamming_calculate(const unsigned char *buf, unsigned int step_size,
 			     unsigned char *code, bool sm_order);
 int nand_ecc_sw_hamming_calculate(struct nand_device *nand,
@@ -44,4 +46,38 @@ int nand_ecc_sw_hamming_correct(struct nand_device *nand, unsigned char *buf,
 				unsigned char *read_ecc,
 				unsigned char *calc_ecc);
 
+#else /* !CONFIG_MTD_NAND_ECC_SW_HAMMING */
+
+static inline int ecc_sw_hamming_calculate(const unsigned char *buf,
+					   unsigned int step_size,
+					   unsigned char *code, bool sm_order)
+{
+	return -ENOTSUPP;
+}
+
+static inline int nand_ecc_sw_hamming_calculate(struct nand_device *nand,
+						const unsigned char *buf,
+						unsigned char *code)
+{
+	return -ENOTSUPP;
+}
+
+static inline int ecc_sw_hamming_correct(unsigned char *buf,
+					 unsigned char *read_ecc,
+					 unsigned char *calc_ecc,
+					 unsigned int step_size, bool sm_order)
+{
+	return -ENOTSUPP;
+}
+
+static inline int nand_ecc_sw_hamming_correct(struct nand_device *nand,
+					      unsigned char *buf,
+					      unsigned char *read_ecc,
+					      unsigned char *calc_ecc)
+{
+	return -ENOTSUPP;
+}
+
+#endif /* CONFIG_MTD_NAND_ECC_SW_HAMMING */
+
 #endif /* __MTD_NAND_ECC_SW_HAMMING_H__ */
-- 
2.20.1