[RFC PATCH 17/27] mtd: nand: ecc: Let the software Hamming ECC engine be unselected

[Miquel Raynal <miquel.raynal@xxxxxxxxxxx>]

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

Signed-off-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
---
 drivers/mtd/nand/ecc/Kconfig               | 10 +++++-
 drivers/mtd/nand/raw/Kconfig               |  2 +-
 include/linux/mtd/nand-sw-hamming-engine.h | 38 ++++++++++++++++++++++
 3 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/nand/ecc/Kconfig b/drivers/mtd/nand/ecc/Kconfig
index e0106b3a7ec1..ff20e621ffef 100644
--- a/drivers/mtd/nand/ecc/Kconfig
+++ b/drivers/mtd/nand/ecc/Kconfig
@@ -1,7 +1,15 @@
 menu "ECC engine support"
 
 config MTD_NAND_ECC_SW_HAMMING
-	tristate
+	tristate "Software Hamming ECC engine"
+	default y
+	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 995fa78bdedb..76a2a8493b1f 100644
--- a/drivers/mtd/nand/raw/Kconfig
+++ b/drivers/mtd/nand/raw/Kconfig
@@ -1,6 +1,5 @@
 menuconfig MTD_RAW_NAND
 	tristate "Raw/Parallel NAND Device Support"
-	select MTD_NAND_ECC_SW_HAMMING
 	help
 	  This enables support for accessing all type of raw/parallel
 	  NAND flash devices. For further information see
@@ -69,6 +68,7 @@ config MTD_NAND_AU1550
 config MTD_NAND_NDFC
 	tristate "IBM/MCC 4xx NAND controller"
 	depends on 4xx
+	depends on 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-sw-hamming-engine.h b/include/linux/mtd/nand-sw-hamming-engine.h
index c50da3a255b7..378ba46f7e1d 100644
--- a/include/linux/mtd/nand-sw-hamming-engine.h
+++ b/include/linux/mtd/nand-sw-hamming-engine.h
@@ -30,6 +30,8 @@ struct 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);
@@ -42,4 +44,40 @@ int __ecc_sw_hamming_correct(unsigned char *buf, unsigned char *read_ecc,
 int 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 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 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__ */
-- 
2.19.1


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