[PATCH v6 1/4] ARM: OMAP2+: cleaned-up DT support of various ECC schemes

[Pekon Gupta <pekon@ti.com>]

OMAP NAND driver support multiple ECC scheme, which can used in following
different flavours, depending on in-build Hardware engines supported by SoC.

+---------------------------------------+---------------+---------------+
| ECC scheme                            |ECC calculation|Error detection|
+---------------------------------------+---------------+---------------+
|OMAP_ECC_HAMMING_CODE_HW               |H/W (GPMC)     |S/W            |
+---------------------------------------+---------------+---------------+
|OMAP_ECC_BCH8_CODE_HW_DETECTION_SW     |H/W (GPMC)     |S/W            |
|(requires CONFIG_MTD_NAND_ECC_BCH)     |               |               |
+---------------------------------------+---------------+---------------+
|OMAP_ECC_BCH8_CODE_HW                  |H/W (GPMC)     |H/W (ELM)      |
|(requires CONFIG_MTD_NAND_OMAP_BCH &&  |               |               |
| ti,elm-id in DT)                      |               |               |
+---------------------------------------+---------------+---------------+
To optimize footprint of omap2-nand driver, selection of some ECC schemes
also require enabling following Kconfigs, in addition to setting appropriate
DT bindings
- Kconfig:CONFIG_MTD_NAND_ECC_BCH        enables S/W based BCH ECC algorithm
- Kconfig:CONFIG_MTD_NAND_OMAP_BCH       enables H/W based BCH ECC algorithm

This patch
- updates DT binding for selection of ecc-scheme
- updates DT binding for detection of ELM h/w engine
- removes following obselete ECC schemes
	OMAP_ECC_HAMMING_CODE_DEFAULT (S/W based 1-bit Hamming ECC)
	OMAP_ECC_HAMMING_CODE_HW_ROMCODE (H/W based 1-bit Hamming ECC scheme)
- updates DT binding documentation for mtd/gpmc-nand

Signed-off-by: Pekon Gupta <pekon@ti.com>
---
 .../devicetree/bindings/mtd/gpmc-nand.txt          | 14 +++----
 arch/arm/mach-omap2/board-flash.c                  |  2 +-
 arch/arm/mach-omap2/gpmc.c                         | 47 +++++++++++++++-------
 include/linux/platform_data/mtd-nand-omap2.h       | 23 +++++++----
 4 files changed, 56 insertions(+), 30 deletions(-)

diff --git a/Documentation/devicetree/bindings/mtd/gpmc-nand.txt b/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
index df338cb..958e5d5 100644
--- a/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
+++ b/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
@@ -21,11 +21,8 @@ Optional properties:
 				is wired that way. If not specified, a bus
 				width of 8 is assumed.
 
- - ti,nand-ecc-opt:		A string setting the ECC layout to use. One of:
-
-		"sw"		Software method (default)
-		"hw"		Hardware method
-		"hw-romcode"	gpmc hamming mode method & romcode layout
+ - ti,nand-ecc-scheme:		A string setting the ECC layout to use. One of:
+		"ham1"		1-bit Hamming ecc code
 		"bch4"		4-bit BCH ecc code
 		"bch8"		8-bit BCH ecc code
 
@@ -36,8 +33,11 @@ Optional properties:
 		"prefetch-dma"		Prefetch enabled sDMA mode
 		"prefetch-irq"		Prefetch enabled irq mode
 
- - elm_id:	Specifies elm device node. This is required to support BCH
- 		error correction using ELM module.
+ - ti,elm-id:	Specifies pHandle of the ELM devicetree node.
+		ELM is an on-chip hardware engine on TI SoC which is used for
+		locating ECC errors for BCHx algorithms. SoC devices which have
+		ELM hardware engines should specify this device node in .dtsi
+		Using ELM for ECC error correction frees some CPU cycles.
 
 For inline partiton table parsing (optional):
 
diff --git a/arch/arm/mach-omap2/board-flash.c b/arch/arm/mach-omap2/board-flash.c
index fc20a61..ac82512 100644
--- a/arch/arm/mach-omap2/board-flash.c
+++ b/arch/arm/mach-omap2/board-flash.c
@@ -142,7 +142,7 @@ __init board_nand_init(struct mtd_partition *nand_parts, u8 nr_parts, u8 cs,
 	board_nand_data.nr_parts	= nr_parts;
 	board_nand_data.devsize		= nand_type;
 
-	board_nand_data.ecc_opt = OMAP_ECC_HAMMING_CODE_DEFAULT;
+	board_nand_data.ecc_opt = OMAP_ECC_BCH8_CODE_HW;
 	gpmc_nand_init(&board_nand_data, gpmc_t);
 }
 #endif /* CONFIG_MTD_NAND_OMAP2 || CONFIG_MTD_NAND_OMAP2_MODULE */
diff --git a/arch/arm/mach-omap2/gpmc.c b/arch/arm/mach-omap2/gpmc.c
index 9f4795a..6409884 100644
--- a/arch/arm/mach-omap2/gpmc.c
+++ b/arch/arm/mach-omap2/gpmc.c
@@ -1340,15 +1340,6 @@ static void __maybe_unused gpmc_read_timings_dt(struct device_node *np,
 }
 
 #ifdef CONFIG_MTD_NAND
-
-static const char * const nand_ecc_opts[] = {
-	[OMAP_ECC_HAMMING_CODE_DEFAULT]		= "sw",
-	[OMAP_ECC_HAMMING_CODE_HW]		= "hw",
-	[OMAP_ECC_HAMMING_CODE_HW_ROMCODE]	= "hw-romcode",
-	[OMAP_ECC_BCH4_CODE_HW]			= "bch4",
-	[OMAP_ECC_BCH8_CODE_HW]			= "bch8",
-};
-
 static const char * const nand_xfer_types[] = {
 	[NAND_OMAP_PREFETCH_POLLED]		= "prefetch-polled",
 	[NAND_OMAP_POLLED]			= "polled",
@@ -1363,6 +1354,8 @@ static int gpmc_probe_nand_child(struct platform_device *pdev,
 	const char *s;
 	struct gpmc_timings gpmc_t;
 	struct omap_nand_platform_data *gpmc_nand_data;
+	const __be32 *parp;
+	int lenp;
 
 	if (of_property_read_u32(child, "reg", &val) < 0) {
 		dev_err(&pdev->dev, "%s has no 'reg' property\n",
@@ -1378,12 +1371,36 @@ static int gpmc_probe_nand_child(struct platform_device *pdev,
 	gpmc_nand_data->cs = val;
 	gpmc_nand_data->of_node = child;
 
-	if (!of_property_read_string(child, "ti,nand-ecc-opt", &s))
-		for (val = 0; val < ARRAY_SIZE(nand_ecc_opts); val++)
-			if (!strcasecmp(s, nand_ecc_opts[val])) {
-				gpmc_nand_data->ecc_opt = val;
-				break;
-			}
+	/* Detect availability of ELM module */
+	parp = of_get_property(child, "ti,elm-id", &lenp);
+	if ((parp == NULL) && (lenp != (sizeof(void *) * 2))) {
+		pr_warn("%s: ti,elm-id property not found\n", __func__);
+		gpmc_nand_data->elm_of_node = NULL;
+	} else {
+		gpmc_nand_data->elm_of_node =
+				of_find_node_by_phandle(be32_to_cpup(parp));
+	}
+	/* select NAND ecc-scheme */
+	if (of_property_read_string(child, "ti,nand-ecc-scheme", &s)) {
+		pr_err("%s: valid ti,nand-ecc-scheme not found\n", __func__);
+		return -ENODEV;
+	}
+	if (!strcmp(s, "ham1"))
+		gpmc_nand_data->ecc_opt = OMAP_ECC_HAMMING_CODE_HW;
+	else if (!strcmp(s, "bch4"))
+		if (gpmc_nand_data->elm_of_node)
+			gpmc_nand_data->ecc_opt = OMAP_ECC_BCH4_CODE_HW;
+		else
+			gpmc_nand_data->ecc_opt =
+				OMAP_ECC_BCH4_CODE_HW_DETECTION_SW;
+	else if (!strcmp(s, "bch8"))
+		if (gpmc_nand_data->elm_of_node)
+			gpmc_nand_data->ecc_opt = OMAP_ECC_BCH8_CODE_HW;
+		else
+			gpmc_nand_data->ecc_opt =
+				OMAP_ECC_BCH8_CODE_HW_DETECTION_SW;
+	else
+		pr_err("%s: ti,ecc-scheme: invalid property value\n", __func__);
 
 	if (!of_property_read_string(child, "ti,nand-xfer-type", &s))
 		for (val = 0; val < ARRAY_SIZE(nand_xfer_types); val++)
diff --git a/include/linux/platform_data/mtd-nand-omap2.h b/include/linux/platform_data/mtd-nand-omap2.h
index 6bf9ef4..b4c2c5a 100644
--- a/include/linux/platform_data/mtd-nand-omap2.h
+++ b/include/linux/platform_data/mtd-nand-omap2.h
@@ -23,13 +23,21 @@ enum nand_io {
 };
 
 enum omap_ecc {
-		/* 1-bit ecc: stored at end of spare area */
-	OMAP_ECC_HAMMING_CODE_DEFAULT = 0, /* Default, s/w method */
-	OMAP_ECC_HAMMING_CODE_HW, /* gpmc to detect the error */
-		/* 1-bit ecc: stored at beginning of spare area as romcode */
-	OMAP_ECC_HAMMING_CODE_HW_ROMCODE, /* gpmc method & romcode layout */
-	OMAP_ECC_BCH4_CODE_HW, /* 4-bit BCH ecc code */
-	OMAP_ECC_BCH8_CODE_HW, /* 8-bit BCH ecc code */
+	/* 1-bit  ECC calculation by Software, Error detection by Software */
+	OMAP_ECC_HAMMING_CODE_DEFAULT = 0,
+	/* 1-bit  ECC calculation by GPMC, Error detection by Software */
+	OMAP_ECC_HAMMING_CODE_HW,
+	/* 1-bit  ECC calculation by GPMC, Error detection by Software */
+	/* ECC layout compatible to legacy ROMCODE. */
+	OMAP_ECC_HAMMING_CODE_HW_ROMCODE,
+	/* 4-bit  ECC calculation by GPMC, Error detection by Software */
+	OMAP_ECC_BCH4_CODE_HW_DETECTION_SW,
+	/* 4-bit  ECC calculation by GPMC, Error detection by ELM */
+	OMAP_ECC_BCH4_CODE_HW,
+	/* 8-bit  ECC calculation by GPMC, Error detection by Software */
+	OMAP_ECC_BCH8_CODE_HW_DETECTION_SW,
+	/* 8-bit  ECC calculation by GPMC, Error detection by ELM */
+	OMAP_ECC_BCH8_CODE_HW,
 };
 
 struct gpmc_nand_regs {
@@ -63,5 +71,6 @@ struct omap_nand_platform_data {
 
 	/* for passing the partitions */
 	struct device_node	*of_node;
+	struct device_node	*elm_of_node;
 };
 #endif
-- 
1.8.1