mtd: nand: omap: add CONFIG_NAND_OMAP_ECCSCHEME for selection of ecc-scheme

This patch adds new CONFIG_NAND_OMAP_ECCSCHEME, replacing other distributed
CONFIG_xx used for selecting NAND ecc-schemes.
This patch aims at solving following issues.

1) Currently ecc-scheme is tied to SoC platform, which prevents user to select
   other ecc-schemes also supported in hardware. like;
 - most of OMAP3 SoC platforms use only 1-bit Hamming ecc-scheme, inspite
   the fact that they can use higher ecc-schemes like 8-bit ecc-schemes with
   software based error detection (OMAP_ECC_BCH4_CODE_HW_DETECTION_SW).
 - most of AM33xx SoC plaforms use 8-bit BCH ecc-scheme for now, but hardware
   supports BCH16 ecc-scheme also.

2) Different platforms use different CONFIG_xx to select ecc-schemes, which
   adds confusion for user while migrating platforms.
 - *CONFIG_NAND_OMAP_ELM* which enables ELM hardware engine, selects only
    8-bit BCH ecc-scheme with h/w based error-correction (OMAP_ECC_BCH8_CODE_HW)
    whereas ELM hardware engine supports other ecc-schemes also like; BCH4,
    and BCH16 (in future).
 - *CONFIG_NAND_OMAP_BCH8* selects 8-bit BCH ecc-scheme with s/w based error
    correction (OMAP_ECC_BCH8_CODE_HW_DETECTION_SW).
 - *CONFIG_SPL_NAND_SOFTECC* selects 1-bit Hamming ecc-scheme using s/w library

Thus adding new *CONFIG_NAND_OMAP_ECCSCHEME* de-couples ecc-scheme dependency
on SoC platform and NAND driver. And user can select ecc-scheme independently
foreach board.
However, selection some hardware based ecc-schemes (OMAP_ECC_BCHx_CODE_HW) still
depends on presence of ELM hardware engine on SoC. (Refer doc/README.nand)

Signed-off-by: Pekon Gupta <pekon@ti.com>

2 files changed, 24 insertions, 2 deletions

diff --git a/doc/README.nand b/doc/README.nand
index 487548fcb8..b91f1985d1 100644
--- a/doc/README.nand
+++ b/doc/README.nand
@@ -208,6 +208,29 @@ Platform specific options
 	detection. However ECC calculation on such plaforms would still be
 	done by GPMC controller.
 
+   CONFIG_NAND_OMAP_ECCSCHEME
+	On OMAP platforms, this CONFIG specifies NAND ECC scheme.
+	It can take following values:
+	OMAP_ECC_HAM1_CODE_SW
+		1-bit Hamming code using software lib.
+		(for legacy devices only)
+	OMAP_ECC_HAM1_CODE_HW
+		1-bit Hamming code using GPMC hardware.
+		(for legacy devices only)
+	OMAP_ECC_BCH4_CODE_HW_DETECTION_SW
+		4-bit BCH code (unsupported)
+	OMAP_ECC_BCH4_CODE_HW
+		4-bit BCH code (unsupported)
+	OMAP_ECC_BCH8_CODE_HW_DETECTION_SW
+		8-bit BCH code with
+		- ecc calculation using GPMC hardware engine,
+		- error detection using software library.
+		- requires CONFIG_BCH to enable software BCH library
+		(For legacy device which do not have ELM h/w engine)
+	OMAP_ECC_BCH8_CODE_HW
+		8-bit BCH code with
+		- ecc calculation using GPMC hardware engine,
+		- error detection using ELM hardware engine.
 
 NOTE:
 =====
diff --git a/doc/README.omap3 b/doc/README.omap3
index 1fbe79db37..a62c357405 100644
--- a/doc/README.omap3
+++ b/doc/README.omap3
@@ -161,8 +161,7 @@ BCH8
 
 To enable hardware assisted BCH8 (8-bit BCH [Bose, Chaudhuri, Hocquenghem]) on
 OMAP3 devices we can use the BCH library in lib/bch.c. To do so add CONFIG_BCH
-to enable the library and CONFIG_NAND_OMAP_BCH8 to to enable hardware assisted
-syndrom generation to your board config.
+and set CONFIG_NAND_OMAP_ECCSCHEME=5 (refer README.nand) for selecting BCH8_SW.
 The NAND OOB layout is the same as in linux kernel, if the linux kernel BCH8
 implementation for OMAP3 works for you so the u-boot version should also.
 When you require the SPL to read with BCH8 there are two more configs to