[PATCH] mtd: nand: fsmc: Add BCH4 SW ECC support for SPEAr600

[Stefan Roese <sr@denx.de>]

This patch adds support for 4-bit ECC BCH4 for the SPEAr600 SoC. This can
be used by boards equipped with a NAND chip that requires 4-bit ECC
strength. The SPEAr600 HW ECC only supports 1-bit ECC strength.

To enable SW BCH4, you need to specify this in your nand controller
DT node:

	nand-ecc-mode = "soft_bch";

Tested on a custom SPEAr600 board.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Brian Norris <computersforpeace@gmail.com>
---
 drivers/mtd/nand/fsmc_nand.c | 72 ++++++++++++++++++++++++++++++++------------
 include/linux/mtd/fsmc.h     |  2 ++
 2 files changed, 54 insertions(+), 20 deletions(-)

diff --git a/drivers/mtd/nand/fsmc_nand.c b/drivers/mtd/nand/fsmc_nand.c
index 793872f..3e01288 100644
--- a/drivers/mtd/nand/fsmc_nand.c
+++ b/drivers/mtd/nand/fsmc_nand.c
@@ -29,9 +29,11 @@
 #include <linux/types.h>
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/nand.h>
+#include <linux/mtd/nand_bch.h>
 #include <linux/mtd/nand_ecc.h>
 #include <linux/platform_device.h>
 #include <linux/of.h>
+#include <linux/of_mtd.h>
 #include <linux/mtd/partitions.h>
 #include <linux/io.h>
 #include <linux/slab.h>
@@ -908,6 +910,13 @@ static int fsmc_nand_probe_config_dt(struct platform_device *pdev,
 		}
 		pdata->bank = val;
 	}
+
+	ret = of_get_nand_ecc_mode(np);
+	if (ret >= 0)
+		pdata->ecc_mode = ret;
+	else
+		pdata->ecc_mode = NAND_ECC_HW;
+
 	return 0;
 }
 #else
@@ -960,7 +969,7 @@ static int __init fsmc_nand_probe(struct platform_device *pdev)
 	host->data_va = devm_ioremap_resource(&pdev->dev, res);
 	if (IS_ERR(host->data_va))
 		return PTR_ERR(host->data_va);
-	
+
 	host->data_pa = (dma_addr_t)res->start;
 
 	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "nand_addr");
@@ -1023,7 +1032,7 @@ static int __init fsmc_nand_probe(struct platform_device *pdev)
 	nand->cmd_ctrl = fsmc_cmd_ctrl;
 	nand->chip_delay = 30;
 
-	nand->ecc.mode = NAND_ECC_HW;
+	nand->ecc.mode = pdata->ecc_mode;
 	nand->ecc.hwctl = fsmc_enable_hwecc;
 	nand->ecc.size = 512;
 	nand->options = pdata->options;
@@ -1071,10 +1080,27 @@ static int __init fsmc_nand_probe(struct platform_device *pdev)
 		nand->ecc.bytes = 13;
 		nand->ecc.strength = 8;
 	} else {
-		nand->ecc.calculate = fsmc_read_hwecc_ecc1;
-		nand->ecc.correct = nand_correct_data;
-		nand->ecc.bytes = 3;
-		nand->ecc.strength = 1;
+		switch (nand->ecc.mode) {
+		case NAND_ECC_HW:
+			dev_info(&pdev->dev, "Using 1-bit HW ECC scheme\n");
+			nand->ecc.calculate = fsmc_read_hwecc_ecc1;
+			nand->ecc.correct = nand_correct_data;
+			nand->ecc.bytes = 3;
+			nand->ecc.strength = 1;
+			break;
+
+		case NAND_ECC_SOFT_BCH:
+			dev_info(&pdev->dev, "Using 4-bit SW BCH ECC scheme\n");
+			nand->ecc.calculate = nand_bch_calculate_ecc;
+			nand->ecc.correct = nand_bch_correct_data;
+			nand->ecc.bytes = 7;
+			nand->ecc.strength = 4;
+			break;
+
+		default:
+			dev_err(&pdev->dev, "Unsupported ECC mode!\n");
+			goto err_scan_ident;
+		}
 	}
 
 	/*
@@ -1114,20 +1140,26 @@ static int __init fsmc_nand_probe(struct platform_device *pdev)
 			BUG();
 		}
 	} else {
-		switch (host->mtd.oobsize) {
-		case 16:
-			nand->ecc.layout = &fsmc_ecc1_16_layout;
-			break;
-		case 64:
-			nand->ecc.layout = &fsmc_ecc1_64_layout;
-			break;
-		case 128:
-			nand->ecc.layout = &fsmc_ecc1_128_layout;
-			break;
-		default:
-			dev_warn(&pdev->dev, "No oob scheme defined for oobsize %d\n",
-				 mtd->oobsize);
-			BUG();
+		/*
+		 * Don't set layout for BCH4 SW ECC. This will be
+		 * generated later in nand_bch_init() later.
+		 */
+		if (nand->ecc.mode != NAND_ECC_SOFT_BCH) {
+			switch (host->mtd.oobsize) {
+			case 16:
+				nand->ecc.layout = &fsmc_ecc1_16_layout;
+				break;
+			case 64:
+				nand->ecc.layout = &fsmc_ecc1_64_layout;
+				break;
+			case 128:
+				nand->ecc.layout = &fsmc_ecc1_128_layout;
+				break;
+			default:
+				dev_warn(&pdev->dev, "No oob scheme defined for oobsize %d\n",
+					 mtd->oobsize);
+				BUG();
+			}
 		}
 	}
 
diff --git a/include/linux/mtd/fsmc.h b/include/linux/mtd/fsmc.h
index c8be32e..dfdbb16 100644
--- a/include/linux/mtd/fsmc.h
+++ b/include/linux/mtd/fsmc.h
@@ -163,6 +163,8 @@ struct fsmc_nand_platform_data {
 	/* priv structures for dma accesses */
 	void			*read_dma_priv;
 	void			*write_dma_priv;
+
+	int			ecc_mode;
 };
 
 extern int __init fsmc_nor_init(struct platform_device *pdev,
-- 
2.5.1