davinci_nand ecc (1-bit) config handling

Update/bugfix hardware ECC config handling.  The driver should still
be able to build without that support enabled (else remove its Kconfig
option!); remove frowned-upon inline #ifdeffery.

Also suffix all the original ECC logic with _1bit to distinguish it
from the DM355's enhanced ECC hardware (corrects 4 single-bit errors
per 512 bytes), which should get good support.

Note that I think the issue with flash access on the DM355 EVM is
likely to be ECC related.  Specifically, the original LSP uses that
enhanced ECC hardware, and thus needs 10 bytes of data per 512 byte
block ... which seems to be stored INLINE rather than in the OOB
region, because of a Linux restriction to 32 bytes of ECC data.
(One hopes that restriction gets lifted ASAP.)
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>

drivers/mtd/nand/davinci_nand.c

@@ -67,9 +67,14 @@ static inline int mtd_has_cmdlinepart(void) { return 0; }
 #endif
 
 #ifdef CONFIG_NAND_FLASH_HW_ECC
-#define DAVINCI_NAND_ECC_MODE NAND_ECC_HW3_512
+static inline int is_hw_ecc_1bit(void) { return 1; }
 #else
-#define DAVINCI_NAND_ECC_MODE NAND_ECC_SOFT
+static inline int is_hw_ecc_1bit(void) { return 0; }
+#define NAND_ECC_HW3_256	100
+#define NAND_ECC_HW3_512	101
+#define NAND_ECC_HW6_512	102
+#define NAND_ECC_HW8_512	103
+#define NAND_ECC_HW12_2048	104
 #endif
 
 #define DRIVER_NAME "davinci_nand"
@@ -151,8 +156,7 @@ static void nand_davinci_select_chip(struct mtd_info *mtd, int chip)
 	/* do nothing */
 }
 
-#ifdef CONFIG_NAND_FLASH_HW_ECC
-static void nand_davinci_enable_hwecc(struct mtd_info *mtd, int mode)
+static void nand_davinci_enable_hwecc_1bit(struct mtd_info *mtd, int mode)
 {
 	struct davinci_nand_info *info;
 	u32 retval;
@@ -171,7 +175,7 @@ static void nand_davinci_enable_hwecc(struct mtd_info *mtd, int mode)
 /*
  * Read DaVinci ECC register
  */
-static u32 nand_davinci_readecc(struct mtd_info *mtd)
+static inline u32 nand_davinci_readecc_1bit(struct mtd_info *mtd)
 {
 	struct davinci_nand_info *info = to_davinci_nand(mtd);
 
@@ -182,10 +186,10 @@ static u32 nand_davinci_readecc(struct mtd_info *mtd)
 /*
  * Read DaVinci ECC registers and rework into MTD format
  */
-static int nand_davinci_calculate_ecc(struct mtd_info *mtd,
+static int nand_davinci_calculate_ecc_1bit(struct mtd_info *mtd,
 				      const u_char *dat, u_char *ecc_code)
 {
-	unsigned int ecc_val = nand_davinci_readecc(mtd);
+	unsigned int ecc_val = nand_davinci_readecc_1bit(mtd);
 	/* squeeze 0 middle bits out so that it fits in 3 bytes */
 	unsigned int tmp = (ecc_val & 0x0fff) | ((ecc_val & 0x0fff0000) >> 4);
 	/* invert so that erased block ecc is correct */
@@ -197,7 +201,7 @@ static int nand_davinci_calculate_ecc(struct mtd_info *mtd,
 	return 0;
 }
 
-static int nand_davinci_correct_data(struct mtd_info *mtd, u_char *dat,
+static int nand_davinci_correct_data_1bit(struct mtd_info *mtd, u_char *dat,
 				     u_char *read_ecc, u_char *calc_ecc)
 {
 	struct nand_chip *chip = mtd->priv;
@@ -228,7 +232,6 @@ static int nand_davinci_correct_data(struct mtd_info *mtd, u_char *dat,
 	}
 	return 0;
 }
-#endif
 
 /*
  * Read OOB data from flash.
@@ -415,7 +418,9 @@ static void __init nand_davinci_set_eccsize(struct nand_chip *chip)
 {
 	chip->ecc.size = 256;
 
-#ifdef CONFIG_NAND_FLASH_HW_ECC
+	if (!is_hw_ecc_1bit())
+		return;
+
 	switch (chip->ecc.mode) {
 	case NAND_ECC_HW12_2048:
 		chip->ecc.size = 2048;
@@ -424,7 +429,7 @@ static void __init nand_davinci_set_eccsize(struct nand_chip *chip)
 	case NAND_ECC_HW3_512:
 	case NAND_ECC_HW6_512:
 	case NAND_ECC_HW8_512:
-	chip->ecc.size = 512;
+		chip->ecc.size = 512;
 		break;
 
 	case NAND_ECC_HW3_256:
@@ -432,14 +437,15 @@ static void __init nand_davinci_set_eccsize(struct nand_chip *chip)
 		/* do nothing */
 		break;
 	}
-#endif
 }
 
 static void __init nand_davinci_set_eccbytes(struct nand_chip *chip)
 {
 	chip->ecc.bytes = 3;
 
-#ifdef CONFIG_NAND_FLASH_HW_ECC
+	if (!is_hw_ecc_1bit())
+		return;
+
 	switch (chip->ecc.mode) {
 	case NAND_ECC_HW12_2048:
 		chip->ecc.bytes += 4;
@@ -453,7 +459,6 @@ static void __init nand_davinci_set_eccbytes(struct nand_chip *chip)
 		/* do nothing */
 		break;
 	}
-#endif
 }
 
 static void __init nand_davinci_flash_init(struct davinci_nand_info *info)
@@ -583,7 +588,6 @@ static int __init nand_davinci_probe(struct platform_device *pdev)
 	info->chip.chip_delay	= 0;
 	info->chip.select_chip	= nand_davinci_select_chip;
 	info->chip.options	= 0;
-	info->chip.ecc.mode	= DAVINCI_NAND_ECC_MODE;
 
 	/* Set address of hardware control function */
 	info->chip.cmd_ctrl	= nand_davinci_hwcontrol;
@@ -596,12 +600,28 @@ static int __init nand_davinci_probe(struct platform_device *pdev)
 	/* Speed up the creation of the bad block table */
 	info->chip.scan_bbt      = nand_davinci_scan_bbt;
 
-#ifdef CONFIG_NAND_FLASH_HW_ECC
-	/* REVISIT should be using runtime check */
-	info->chip.ecc.calculate = nand_davinci_calculate_ecc;
-	info->chip.ecc.correct   = nand_davinci_correct_data;
-	info->chip.ecc.hwctl     = nand_davinci_enable_hwecc;
-#endif
+	/*
+	 * REVISIT should probably be using runtime check using board's
+	 * platform_data, since three ECC modes (soft, 1bit, 4bit) are
+	 * incompatible at the binary level.  If the board formatted its
+	 * flash for a mode that's not supported by this kernel, bail!
+	 *
+	 * REVISIT dm355 adds an ECC mode that corrects up to 4 error
+	 * bits, using 10 ECC bytes every 512 bytes of data.  And that
+	 * is what TI's original LSP uses... along with quite a hacked
+	 * up "inline OOB" scheme storing those ECC bytes, which happens
+	 * to use (in good blocks) bytes used by factory bad-block marks
+	 * (in bad blocks).  There was evidently a technical issue (now
+	 * fixed?):  Linux seemed to limit ECC data to 32 bytes.
+	 */
+	if (is_hw_ecc_1bit()) {
+		info->chip.ecc.mode	 = NAND_ECC_HW3_512;
+		info->chip.ecc.calculate = nand_davinci_calculate_ecc_1bit;
+		info->chip.ecc.correct   = nand_davinci_correct_data_1bit;
+		info->chip.ecc.hwctl     = nand_davinci_enable_hwecc_1bit;
+	} else {
+		info->chip.ecc.mode	 = NAND_ECC_SOFT;
+	}
 
 	info->clk = clk_get(&pdev->dev, "AEMIFCLK");
 	if (IS_ERR(info->clk)) {