mtd: nand: davinci_nand, 4-bit ECC for smallpage

Minimal support for the 4-bit ECC engine found on DM355, DM365,
DA830/OMAP-L137, and similar recent DaVinci-family chips.

This is limited to small-page flash for now; there are some page
layout issues for large page chips.  Note that most boards using
this engine (like the DM355 EVM) include 2GiB large page chips.

Sanity tested on DM355 EVM after swapping the socketed NAND for
a small-page one.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

arch/arm/mach-davinci/include/mach/nand.h

@@ -68,10 +68,14 @@ struct davinci_nand_pdata {		/* platform_data */
 
 	/* none  == NAND_ECC_NONE (strongly *not* advised!!)
 	 * soft  == NAND_ECC_SOFT
-	 * 1-bit == NAND_ECC_HW
-	 * 4-bit == NAND_ECC_HW_SYNDROME (not on all chips)
+	 * else  == NAND_ECC_HW, according to ecc_bits
+	 *
+	 * All DaVinci-family chips support 1-bit hardware ECC.
+	 * Newer ones also support 4-bit ECC, but are awkward
+	 * using it with large page chips.
 	 */
 	nand_ecc_modes_t	ecc_mode;
+	u8			ecc_bits;
 
 	/* e.g. NAND_BUSWIDTH_16 or NAND_USE_FLASH_BBT */
 	unsigned		options;

drivers/mtd/nand/davinci_nand.c

@@ -44,7 +44,7 @@
  * and some flavors of secondary chipselect (e.g. based on A12) as used
  * with multichip packages.
  *
- * The 1-bit ECC hardware is supported, but not yet the newer 4-bit ECC
+ * The 1-bit ECC hardware is supported, as well as the newer 4-bit ECC
  * available on chips like the DM355 and OMAP-L137 and needed with the
  * more error-prone MLC NAND chips.
  *
@@ -54,11 +54,14 @@
 struct davinci_nand_info {
 	struct mtd_info		mtd;
 	struct nand_chip	chip;
+	struct nand_ecclayout	ecclayout;
 
 	struct device		*dev;
 	struct clk		*clk;
 	bool			partitioned;
 
+	bool			is_readmode;
+
 	void __iomem		*base;
 	void __iomem		*vaddr;
 
@@ -73,6 +76,7 @@ struct davinci_nand_info {
 };
 
 static DEFINE_SPINLOCK(davinci_nand_lock);
+static bool ecc4_busy;
 
 #define to_davinci_nand(m) container_of(m, struct davinci_nand_info, mtd)
 
@@ -217,6 +221,192 @@ static int nand_davinci_correct_1bit(struct mtd_info *mtd, u_char *dat,
 
 /*----------------------------------------------------------------------*/
 
+/*
+ * 4-bit hardware ECC ... context maintained over entire AEMIF
+ *
+ * This is a syndrome engine, but we avoid NAND_ECC_HW_SYNDROME
+ * since that forces use of a problematic "infix OOB" layout.
+ * Among other things, it trashes manufacturer bad block markers.
+ * Also, and specific to this hardware, it ECC-protects the "prepad"
+ * in the OOB ... while having ECC protection for parts of OOB would
+ * seem useful, the current MTD stack sometimes wants to update the
+ * OOB without recomputing ECC.
+ */
+
+static void nand_davinci_hwctl_4bit(struct mtd_info *mtd, int mode)
+{
+	struct davinci_nand_info *info = to_davinci_nand(mtd);
+	unsigned long flags;
+	u32 val;
+
+	spin_lock_irqsave(&davinci_nand_lock, flags);
+
+	/* Start 4-bit ECC calculation for read/write */
+	val = davinci_nand_readl(info, NANDFCR_OFFSET);
+	val &= ~(0x03 << 4);
+	val |= (info->core_chipsel << 4) | BIT(12);
+	davinci_nand_writel(info, NANDFCR_OFFSET, val);
+
+	info->is_readmode = (mode == NAND_ECC_READ);
+
+	spin_unlock_irqrestore(&davinci_nand_lock, flags);
+}
+
+/* Read raw ECC code after writing to NAND. */
+static void
+nand_davinci_readecc_4bit(struct davinci_nand_info *info, u32 code[4])
+{
+	const u32 mask = 0x03ff03ff;
+
+	code[0] = davinci_nand_readl(info, NAND_4BIT_ECC1_OFFSET) & mask;
+	code[1] = davinci_nand_readl(info, NAND_4BIT_ECC2_OFFSET) & mask;
+	code[2] = davinci_nand_readl(info, NAND_4BIT_ECC3_OFFSET) & mask;
+	code[3] = davinci_nand_readl(info, NAND_4BIT_ECC4_OFFSET) & mask;
+}
+
+/* Terminate read ECC; or return ECC (as bytes) of data written to NAND. */
+static int nand_davinci_calculate_4bit(struct mtd_info *mtd,
+		const u_char *dat, u_char *ecc_code)
+{
+	struct davinci_nand_info *info = to_davinci_nand(mtd);
+	u32 raw_ecc[4], *p;
+	unsigned i;
+
+	/* After a read, terminate ECC calculation by a dummy read
+	 * of some 4-bit ECC register.  ECC covers everything that
+	 * was read; correct() just uses the hardware state, so
+	 * ecc_code is not needed.
+	 */
+	if (info->is_readmode) {
+		davinci_nand_readl(info, NAND_4BIT_ECC1_OFFSET);
+		return 0;
+	}
+
+	/* Pack eight raw 10-bit ecc values into ten bytes, making
+	 * two passes which each convert four values (in upper and
+	 * lower halves of two 32-bit words) into five bytes.  The
+	 * ROM boot loader uses this same packing scheme.
+	 */
+	nand_davinci_readecc_4bit(info, raw_ecc);
+	for (i = 0, p = raw_ecc; i < 2; i++, p += 2) {
+		*ecc_code++ =   p[0]        & 0xff;
+		*ecc_code++ = ((p[0] >>  8) & 0x03) | ((p[0] >> 14) & 0xfc);
+		*ecc_code++ = ((p[0] >> 22) & 0x0f) | ((p[1] <<  4) & 0xf0);
+		*ecc_code++ = ((p[1] >>  4) & 0x3f) | ((p[1] >> 10) & 0xc0);
+		*ecc_code++ =  (p[1] >> 18) & 0xff;
+	}
+
+	return 0;
+}
+
+/* Correct up to 4 bits in data we just read, using state left in the
+ * hardware plus the ecc_code computed when it was first written.
+ */
+static int nand_davinci_correct_4bit(struct mtd_info *mtd,
+		u_char *data, u_char *ecc_code, u_char *null)
+{
+	int i;
+	struct davinci_nand_info *info = to_davinci_nand(mtd);
+	unsigned short ecc10[8];
+	unsigned short *ecc16;
+	u32 syndrome[4];
+	unsigned num_errors, corrected;
+
+	/* All bytes 0xff?  It's an erased page; ignore its ECC. */
+	for (i = 0; i < 10; i++) {
+		if (ecc_code[i] != 0xff)
+			goto compare;
+	}
+	return 0;
+
+compare:
+	/* Unpack ten bytes into eight 10 bit values.  We know we're
+	 * little-endian, and use type punning for less shifting/masking.
+	 */
+	if (WARN_ON(0x01 & (unsigned) ecc_code))
+		return -EINVAL;
+	ecc16 = (unsigned short *)ecc_code;
+
+	ecc10[0] =  (ecc16[0] >>  0) & 0x3ff;
+	ecc10[1] = ((ecc16[0] >> 10) & 0x3f) | ((ecc16[1] << 6) & 0x3c0);
+	ecc10[2] =  (ecc16[1] >>  4) & 0x3ff;
+	ecc10[3] = ((ecc16[1] >> 14) & 0x3)  | ((ecc16[2] << 2) & 0x3fc);
+	ecc10[4] =  (ecc16[2] >>  8)         | ((ecc16[3] << 8) & 0x300);
+	ecc10[5] =  (ecc16[3] >>  2) & 0x3ff;
+	ecc10[6] = ((ecc16[3] >> 12) & 0xf)  | ((ecc16[4] << 4) & 0x3f0);
+	ecc10[7] =  (ecc16[4] >>  6) & 0x3ff;
+
+	/* Tell ECC controller about the expected ECC codes. */
+	for (i = 7; i >= 0; i--)
+		davinci_nand_writel(info, NAND_4BIT_ECC_LOAD_OFFSET, ecc10[i]);
+
+	/* Allow time for syndrome calculation ... then read it.
+	 * A syndrome of all zeroes 0 means no detected errors.
+	 */
+	davinci_nand_readl(info, NANDFSR_OFFSET);
+	nand_davinci_readecc_4bit(info, syndrome);
+	if (!(syndrome[0] | syndrome[1] | syndrome[2] | syndrome[3]))
+		return 0;
+
+	/* Start address calculation, and wait for it to complete.
+	 * We _could_ start reading more data while this is working,
+	 * to speed up the overall page read.
+	 */
+	davinci_nand_writel(info, NANDFCR_OFFSET,
+			davinci_nand_readl(info, NANDFCR_OFFSET) | BIT(13));
+	for (;;) {
+		u32	fsr = davinci_nand_readl(info, NANDFSR_OFFSET);
+
+		switch ((fsr >> 8) & 0x0f) {
+		case 0:		/* no error, should not happen */
+			return 0;
+		case 1:		/* five or more errors detected */
+			return -EIO;
+		case 2:		/* error addresses computed */
+		case 3:
+			num_errors = 1 + ((fsr >> 16) & 0x03);
+			goto correct;
+		default:	/* still working on it */
+			cpu_relax();
+			continue;
+		}
+	}
+
+correct:
+	/* correct each error */
+	for (i = 0, corrected = 0; i < num_errors; i++) {
+		int error_address, error_value;
+
+		if (i > 1) {
+			error_address = davinci_nand_readl(info,
+						NAND_ERR_ADD2_OFFSET);
+			error_value = davinci_nand_readl(info,
+						NAND_ERR_ERRVAL2_OFFSET);
+		} else {
+			error_address = davinci_nand_readl(info,
+						NAND_ERR_ADD1_OFFSET);
+			error_value = davinci_nand_readl(info,
+						NAND_ERR_ERRVAL1_OFFSET);
+		}
+
+		if (i & 1) {
+			error_address >>= 16;
+			error_value >>= 16;
+		}
+		error_address &= 0x3ff;
+		error_address = (512 + 7) - error_address;
+
+		if (error_address < 512) {
+			data[error_address] ^= error_value;
+			corrected++;
+		}
+	}
+
+	return corrected;
+}
+
+/*----------------------------------------------------------------------*/
+
 /*
  * NOTE:  NAND boot requires ALE == EM_A[1], CLE == EM_A[2], so that's
  * how these chips are normally wired.  This translates to both 8 and 16
@@ -294,6 +484,23 @@ static void __init nand_dm6446evm_flash_init(struct davinci_nand_info *info)
 
 /*----------------------------------------------------------------------*/
 
+/* An ECC layout for using 4-bit ECC with small-page flash, storing
+ * ten ECC bytes plus the manufacturer's bad block marker byte, and
+ * and not overlapping the default BBT markers.
+ */
+static struct nand_ecclayout hwecc4_small __initconst = {
+	.eccbytes = 10,
+	.eccpos = { 0, 1, 2, 3, 4,
+		/* offset 5 holds the badblock marker */
+		6, 7,
+		13, 14, 15, },
+	.oobfree = {
+		{.offset = 8, .length = 5, },
+		{.offset = 16, },
+	},
+};
+
+
 static int __init nand_davinci_probe(struct platform_device *pdev)
 {
 	struct davinci_nand_pdata	*pdata = pdev->dev.platform_data;
@@ -378,24 +585,41 @@ static int __init nand_davinci_probe(struct platform_device *pdev)
 	/* Use board-specific ECC config */
 	ecc_mode		= pdata->ecc_mode;
 
+	ret = -EINVAL;
 	switch (ecc_mode) {
 	case NAND_ECC_NONE:
 	case NAND_ECC_SOFT:
+		pdata->ecc_bits = 0;
 		break;
 	case NAND_ECC_HW:
-		info->chip.ecc.calculate = nand_davinci_calculate_1bit;
-		info->chip.ecc.correct = nand_davinci_correct_1bit;
-		info->chip.ecc.hwctl = nand_davinci_hwctl_1bit;
+		if (pdata->ecc_bits == 4) {
+			/* No sanity checks:  CPUs must support this,
+			 * and the chips may not use NAND_BUSWIDTH_16.
+			 */
+
+			/* No sharing 4-bit hardware between chipselects yet */
+			spin_lock_irq(&davinci_nand_lock);
+			if (ecc4_busy)
+				ret = -EBUSY;
+			else
+				ecc4_busy = true;
+			spin_unlock_irq(&davinci_nand_lock);
+
+			if (ret == -EBUSY)
+				goto err_ecc;
+
+			info->chip.ecc.calculate = nand_davinci_calculate_4bit;
+			info->chip.ecc.correct = nand_davinci_correct_4bit;
+			info->chip.ecc.hwctl = nand_davinci_hwctl_4bit;
+			info->chip.ecc.bytes = 10;
+		} else {
+			info->chip.ecc.calculate = nand_davinci_calculate_1bit;
+			info->chip.ecc.correct = nand_davinci_correct_1bit;
+			info->chip.ecc.hwctl = nand_davinci_hwctl_1bit;
+			info->chip.ecc.bytes = 3;
+		}
 		info->chip.ecc.size = 512;
-		info->chip.ecc.bytes = 3;
 		break;
-	case NAND_ECC_HW_SYNDROME:
-		/* FIXME implement */
-		info->chip.ecc.size = 512;
-		info->chip.ecc.bytes = 10;
-
-		dev_warn(&pdev->dev, "4-bit ECC nyet supported\n");
-		/* FALL THROUGH */
 	default:
 		ret = -EINVAL;
 		goto err_ecc;
@@ -435,12 +659,56 @@ static int __init nand_davinci_probe(struct platform_device *pdev)
 	spin_unlock_irq(&davinci_nand_lock);
 
 	/* Scan to find existence of the device(s) */
-	ret = nand_scan(&info->mtd, pdata->mask_chipsel ? 2 : 1);
+	ret = nand_scan_ident(&info->mtd, pdata->mask_chipsel ? 2 : 1);
 	if (ret < 0) {
 		dev_dbg(&pdev->dev, "no NAND chip(s) found\n");
 		goto err_scan;
 	}
 
+	/* Update ECC layout if needed ... for 1-bit HW ECC, the default
+	 * is OK, but it allocates 6 bytes when only 3 are needed (for
+	 * each 512 bytes).  For the 4-bit HW ECC, that default is not
+	 * usable:  10 bytes are needed, not 6.
+	 */
+	if (pdata->ecc_bits == 4) {
+		int	chunks = info->mtd.writesize / 512;
+
+		if (!chunks || info->mtd.oobsize < 16) {
+			dev_dbg(&pdev->dev, "too small\n");
+			ret = -EINVAL;
+			goto err_scan;
+		}
+
+		/* For small page chips, preserve the manufacturer's
+		 * badblock marking data ... and make sure a flash BBT
+		 * table marker fits in the free bytes.
+		 */
+		if (chunks == 1) {
+			info->ecclayout = hwecc4_small;
+			info->ecclayout.oobfree[1].length =
+				info->mtd.oobsize - 16;
+			goto syndrome_done;
+		}
+
+		/* For large page chips we'll be wanting to use a
+		 * not-yet-implemented mode that reads OOB data
+		 * before reading the body of the page, to avoid
+		 * the "infix OOB" model of NAND_ECC_HW_SYNDROME
+		 * (and preserve manufacturer badblock markings).
+		 */
+		dev_warn(&pdev->dev, "no 4-bit ECC support yet "
+				"for large page NAND\n");
+		ret = -EIO;
+		goto err_scan;
+
+syndrome_done:
+		info->chip.ecc.layout = &info->ecclayout;
+	}
+
+	ret = nand_scan_tail(&info->mtd);
+	if (ret < 0)
+		goto err_scan;
+
 	if (mtd_has_partitions()) {
 		struct mtd_partition	*mtd_parts = NULL;
 		int			mtd_parts_nb = 0;
@@ -503,6 +771,11 @@ static int __init nand_davinci_probe(struct platform_device *pdev)
 err_clk_enable:
 	clk_put(info->clk);
 
+	spin_lock_irq(&davinci_nand_lock);
+	if (ecc_mode == NAND_ECC_HW_SYNDROME)
+		ecc4_busy = false;
+	spin_unlock_irq(&davinci_nand_lock);
+
 err_ecc:
 err_clk:
 err_ioremap:
@@ -526,6 +799,11 @@ static int __exit nand_davinci_remove(struct platform_device *pdev)
 	else
 		status = del_mtd_device(&info->mtd);
 
+	spin_lock_irq(&davinci_nand_lock);
+	if (info->chip.ecc.mode == NAND_ECC_HW_SYNDROME)
+		ecc4_busy = false;
+	spin_unlock_irq(&davinci_nand_lock);
+
 	iounmap(info->base);
 	iounmap(info->vaddr);