mtd: nand: add driver for diskonchip g4 nand flash

This patch adds a driver for the diskonchip G4 nand flash device.  It is based
on the driver from the linux kernel.

This also includes a separate SPL driver.  A separate SPL driver is used because
the device operates in a different mode (reliable mode) when loading a boot
image, and also because the storage format of the boot image is different from
normal data (pages are stored redundantly).  The SPL driver basically mimics how
a typical IPL reads data from the device.  The special operating mode and
storage format are used to compensate for the fact that the IPL does not contain
the BCH ecc decoding algorithm (due to size constraints).  Although the u-boot
SPL *could* use ecc, it operates like an IPL for the sake of simplicity and
uniformity, since the IPL and SPL share the task of loading the u-boot image.
As a side benefit, the SPL driver is very small.

[port from linux kernel 3.4 commit 570469f3bde7f71cc1ece07a18d54a05b6a8775d]

Signed-off-by: Mike Dunn <mikedunn@newsguy.com>

1 files changed, 1028 insertions, 0 deletions

diff --git a/drivers/mtd/nand/docg4.c b/drivers/mtd/nand/docg4.c
new file mode 100644
index 0000000..7dd9953
--- /dev/null
+++ b/drivers/mtd/nand/docg4.c
@@ -0,0 +1,1028 @@
+/*
+ * drivers/mtd/nand/docg4.c
+ *
+ * Copyright (C) 2013 Mike Dunn <mikedunn@newsguy.com>
+ *
+ * This file is released under the terms of GPL v2 and any later version.
+ * See the file COPYING in the root directory of the source tree for details.
+ *
+ * mtd nand driver for M-Systems DiskOnChip G4
+ *
+ * Tested on the Palm Treo 680.  The G4 is also present on Toshiba Portege, Asus
+ * P526, some HTC smartphones (Wizard, Prophet, ...), O2 XDA Zinc, maybe others.
+ * Should work on these as well.  Let me know!
+ *
+ * TODO:
+ *
+ *  Mechanism for management of password-protected areas
+ *
+ *  Hamming ecc when reading oob only
+ *
+ *  According to the M-Sys documentation, this device is also available in a
+ *  "dual-die" configuration having a 256MB capacity, but no mechanism for
+ *  detecting this variant is documented.  Currently this driver assumes 128MB
+ *  capacity.
+ *
+ *  Support for multiple cascaded devices ("floors").  Not sure which gadgets
+ *  contain multiple G4s in a cascaded configuration, if any.
+ *
+ */
+
+
+#include <common.h>
+#include <asm/arch/hardware.h>
+#include <asm/io.h>
+#include <asm/bitops.h>
+#include <asm/errno.h>
+#include <malloc.h>
+#include <nand.h>
+#include <linux/bch.h>
+#include <linux/bitrev.h>
+#include <linux/mtd/docg4.h>
+
+/*
+ * The device has a nop register which M-Sys claims is for the purpose of
+ * inserting precise delays.  But beware; at least some operations fail if the
+ * nop writes are replaced with a generic delay!
+ */
+static inline void write_nop(void __iomem *docptr)
+{
+	writew(0, docptr + DOC_NOP);
+}
+
+
+static int poll_status(void __iomem *docptr)
+{
+	/*
+	 * Busy-wait for the FLASHREADY bit to be set in the FLASHCONTROL
+	 * register.  Operations known to take a long time (e.g., block erase)
+	 * should sleep for a while before calling this.
+	 */
+
+	uint8_t flash_status;
+
+	/* hardware quirk requires reading twice initially */
+	flash_status = readb(docptr + DOC_FLASHCONTROL);
+
+	do {
+		flash_status = readb(docptr + DOC_FLASHCONTROL);
+	} while (!(flash_status & DOC_CTRL_FLASHREADY));
+
+	return 0;
+}
+
+static void write_addr(void __iomem *docptr, uint32_t docg4_addr)
+{
+	/* write the four address bytes packed in docg4_addr to the device */
+
+	writeb(docg4_addr & 0xff, docptr + DOC_FLASHADDRESS);
+	docg4_addr >>= 8;
+	writeb(docg4_addr & 0xff, docptr + DOC_FLASHADDRESS);
+	docg4_addr >>= 8;
+	writeb(docg4_addr & 0xff, docptr + DOC_FLASHADDRESS);
+	docg4_addr >>= 8;
+	writeb(docg4_addr & 0xff, docptr + DOC_FLASHADDRESS);
+}
+
+/*
+ * This is a module parameter in the linux kernel version of this driver.  It is
+ * hard-coded to 'off' for u-boot.  This driver uses oob to mark bad blocks.
+ * This can be problematic when dealing with data not intended for the mtd/nand
+ * subsystem.  For example, on boards that boot from the docg4 and use the IPL
+ * to load an spl + u-boot image, the blocks containing the image will be
+ * reported as "bad" because the oob of the first page of each block contains a
+ * magic number that the IPL looks for, which causes the badblock scan to
+ * erroneously add them to the bad block table.  To erase such a block, use
+ * u-boot's 'nand scrub'.  scrub is safe for the docg4.  The device does have a
+ * factory bad block table, but it is read-only, and is used in conjunction with
+ * oob bad block markers that are written by mtd/nand when a block is deemed to
+ * be bad.  To read data from "bad" blocks, use 'read.raw'.  Unfortunately,
+ * read.raw does not use ecc, which would still work fine on such misidentified
+ * bad blocks.  TODO: u-boot nand utilities need the ability to ignore bad
+ * blocks.
+ */
+static const int ignore_badblocks; /* remains false */
+
+struct docg4_priv {
+	int status;
+	struct {
+		unsigned int command;
+		int column;
+		int page;
+	} last_command;
+	uint8_t oob_buf[16];
+	uint8_t ecc_buf[7];
+	int oob_page;
+	struct bch_control *bch;
+};
+/*
+ * Oob bytes 0 - 6 are available to the user.
+ * Byte 7 is hamming ecc for first 7 bytes.  Bytes 8 - 14 are hw-generated ecc.
+ * Byte 15 (the last) is used by the driver as a "page written" flag.
+ */
+static struct nand_ecclayout docg4_oobinfo = {
+	.eccbytes = 9,
+	.eccpos = {7, 8, 9, 10, 11, 12, 13, 14, 15},
+	.oobavail = 7,
+	.oobfree = { {0, 7} }
+};
+
+static void reset(void __iomem *docptr)
+{
+	/* full device reset */
+
+	writew(DOC_ASICMODE_RESET | DOC_ASICMODE_MDWREN, docptr + DOC_ASICMODE);
+	writew(~(DOC_ASICMODE_RESET | DOC_ASICMODE_MDWREN),
+	       docptr + DOC_ASICMODECONFIRM);
+	write_nop(docptr);
+
+	writew(DOC_ASICMODE_NORMAL | DOC_ASICMODE_MDWREN,
+	       docptr + DOC_ASICMODE);
+	writew(~(DOC_ASICMODE_NORMAL | DOC_ASICMODE_MDWREN),
+	       docptr + DOC_ASICMODECONFIRM);
+
+	writew(DOC_ECCCONF1_ECC_ENABLE, docptr + DOC_ECCCONF1);
+
+	poll_status(docptr);
+}
+
+static void docg4_select_chip(struct mtd_info *mtd, int chip)
+{
+	/*
+	 * Select among multiple cascaded chips ("floors").  Multiple floors are
+	 * not yet supported, so the only valid non-negative value is 0.
+	 */
+	void __iomem *docptr = CONFIG_SYS_NAND_BASE;
+
+	if (chip < 0)
+		return;		/* deselected */
+
+	if (chip > 0)
+		printf("multiple floors currently unsupported\n");
+
+	writew(0, docptr + DOC_DEVICESELECT);
+}
+
+static void read_hw_ecc(void __iomem *docptr, uint8_t *ecc_buf)
+{
+	/* read the 7 hw-generated ecc bytes */
+
+	int i;
+	for (i = 0; i < 7; i++) { /* hw quirk; read twice */
+		ecc_buf[i] = readb(docptr + DOC_BCH_SYNDROM(i));
+		ecc_buf[i] = readb(docptr + DOC_BCH_SYNDROM(i));
+	}
+}
+
+static int correct_data(struct mtd_info *mtd, uint8_t *buf, int page)
+{
+	/*
+	 * Called after a page read when hardware reports bitflips.
+	 * Up to four bitflips can be corrected.
+	 */
+
+	struct nand_chip *nand = mtd->priv;
+	struct docg4_priv *doc = nand->priv;
+	void __iomem *docptr = CONFIG_SYS_NAND_BASE;
+	int i, numerrs;
+	unsigned int errpos[4];
+	const uint8_t blank_read_hwecc[8] = {
+		0xcf, 0x72, 0xfc, 0x1b, 0xa9, 0xc7, 0xb9, 0 };
+
+	read_hw_ecc(docptr, doc->ecc_buf); /* read 7 hw-generated ecc bytes */
+
+	/* check if read error is due to a blank page */
+	if (!memcmp(doc->ecc_buf, blank_read_hwecc, 7))
+		return 0;	/* yes */
+
+	/* skip additional check of "written flag" if ignore_badblocks */
+	if (!ignore_badblocks) {
+		/*
+		 * If the hw ecc bytes are not those of a blank page, there's
+		 * still a chance that the page is blank, but was read with
+		 * errors.  Check the "written flag" in last oob byte, which
+		 * is set to zero when a page is written.  If more than half
+		 * the bits are set, assume a blank page.  Unfortunately, the
+		 * bit flips(s) are not reported in stats.
+		 */
+
+		if (doc->oob_buf[15]) {
+			int bit, numsetbits = 0;
+			unsigned long written_flag = doc->oob_buf[15];
+
+			for (bit = 0; bit < 8; bit++) {
+				if (written_flag & 0x01)
+					numsetbits++;
+				written_flag >>= 1;
+			}
+			if (numsetbits > 4) { /* assume blank */
+				printf("errors in blank page at offset %08x\n",
+				       page * DOCG4_PAGE_SIZE);
+				return 0;
+			}
+		}
+	}
+
+	/*
+	 * The hardware ecc unit produces oob_ecc ^ calc_ecc.  The kernel's bch
+	 * algorithm is used to decode this.  However the hw operates on page
+	 * data in a bit order that is the reverse of that of the bch alg,
+	 * requiring that the bits be reversed on the result.  Thanks to Ivan
+	 * Djelic for his analysis!
+	 */
+	for (i = 0; i < 7; i++)
+		doc->ecc_buf[i] = bitrev8(doc->ecc_buf[i]);
+
+	numerrs = decode_bch(doc->bch, NULL, DOCG4_USERDATA_LEN, NULL,
+			     doc->ecc_buf, NULL, errpos);
+
+	if (numerrs == -EBADMSG) {
+		printf("uncorrectable errors at offset %08x\n",
+		       page * DOCG4_PAGE_SIZE);
+		return -EBADMSG;
+	}
+
+	BUG_ON(numerrs < 0);	/* -EINVAL, or anything other than -EBADMSG */
+
+	/* undo last step in BCH alg (modulo mirroring not needed) */
+	for (i = 0; i < numerrs; i++)
+		errpos[i] = (errpos[i] & ~7)|(7-(errpos[i] & 7));
+
+	/* fix the errors */
+	for (i = 0; i < numerrs; i++) {
+		/* ignore if error within oob ecc bytes */
+		if (errpos[i] > DOCG4_USERDATA_LEN * 8)
+			continue;
+
+		/* if error within oob area preceeding ecc bytes... */
+		if (errpos[i] > DOCG4_PAGE_SIZE * 8)
+			__change_bit(errpos[i] - DOCG4_PAGE_SIZE * 8,
+				     (unsigned long *)doc->oob_buf);
+
+		else    /* error in page data */
+			__change_bit(errpos[i], (unsigned long *)buf);
+	}
+
+	printf("%d error(s) corrected at offset %08x\n",
+	       numerrs, page * DOCG4_PAGE_SIZE);
+
+	return numerrs;
+}
+
+static int read_progstatus(struct docg4_priv *doc, void __iomem *docptr)
+{
+	/*
+	 * This apparently checks the status of programming.  Done after an
+	 * erasure, and after page data is written.  On error, the status is
+	 * saved, to be later retrieved by the nand infrastructure code.
+	 */
+
+	/* status is read from the I/O reg */
+	uint16_t status1 = readw(docptr + DOC_IOSPACE_DATA);
+	uint16_t status2 = readw(docptr + DOC_IOSPACE_DATA);
+	uint16_t status3 = readw(docptr + DOCG4_MYSTERY_REG);
+
+	MTDDEBUG(MTD_DEBUG_LEVEL3, "docg4: %s: %02x %02x %02x\n",
+	    __func__, status1, status2, status3);
+
+	if (status1 != DOCG4_PROGSTATUS_GOOD ||
+	    status2 != DOCG4_PROGSTATUS_GOOD_2 ||
+	    status3 != DOCG4_PROGSTATUS_GOOD_2) {
+		doc->status = NAND_STATUS_FAIL;
+		printf("read_progstatus failed: %02x, %02x, %02x\n",
+		       status1, status2, status3);
+		return -EIO;
+	}
+	return 0;
+}
+
+static int pageprog(struct mtd_info *mtd)
+{
+	/*
+	 * Final step in writing a page.  Writes the contents of its
+	 * internal buffer out to the flash array, or some such.
+	 */
+
+	struct nand_chip *nand = mtd->priv;
+	struct docg4_priv *doc = nand->priv;
+	void __iomem *docptr = CONFIG_SYS_NAND_BASE;
+	int retval = 0;
+
+	MTDDEBUG(MTD_DEBUG_LEVEL3, "docg4: %s\n", __func__);
+
+	writew(DOCG4_SEQ_PAGEPROG, docptr + DOC_FLASHSEQUENCE);
+	writew(DOC_CMD_PROG_CYCLE2, docptr + DOC_FLASHCOMMAND);
+	write_nop(docptr);
+	write_nop(docptr);
+
+	/* Just busy-wait; usleep_range() slows things down noticeably. */
+	poll_status(docptr);
+
+	writew(DOCG4_SEQ_FLUSH, docptr + DOC_FLASHSEQUENCE);
+	writew(DOCG4_CMD_FLUSH, docptr + DOC_FLASHCOMMAND);
+	writew(DOC_ECCCONF0_READ_MODE | 4, docptr + DOC_ECCCONF0);
+	write_nop(docptr);
+	write_nop(docptr);
+	write_nop(docptr);
+	write_nop(docptr);
+	write_nop(docptr);
+
+	retval = read_progstatus(doc, docptr);
+	writew(0, docptr + DOC_DATAEND);
+	write_nop(docptr);
+	poll_status(docptr);
+	write_nop(docptr);
+
+	return retval;
+}
+
+static void sequence_reset(void __iomem *docptr)
+{
+	/* common starting sequence for all operations */
+
+	writew(DOC_CTRL_UNKNOWN | DOC_CTRL_CE, docptr + DOC_FLASHCONTROL);
+	writew(DOC_SEQ_RESET, docptr + DOC_FLASHSEQUENCE);
+	writew(DOC_CMD_RESET, docptr + DOC_FLASHCOMMAND);
+	write_nop(docptr);
+	write_nop(docptr);
+	poll_status(docptr);
+	write_nop(docptr);
+}
+
+static void read_page_prologue(void __iomem *docptr, uint32_t docg4_addr)
+{
+	/* first step in reading a page */
+
+	sequence_reset(docptr);
+
+	writew(DOCG4_SEQ_PAGE_READ, docptr + DOC_FLASHSEQUENCE);
+	writew(DOCG4_CMD_PAGE_READ, docptr + DOC_FLASHCOMMAND);
+	write_nop(docptr);
+
+	write_addr(docptr, docg4_addr);
+
+	write_nop(docptr);
+	writew(DOCG4_CMD_READ2, docptr + DOC_FLASHCOMMAND);
+	write_nop(docptr);
+	write_nop(docptr);
+
+	poll_status(docptr);
+}
+
+static void write_page_prologue(void __iomem *docptr, uint32_t docg4_addr)
+{
+	/* first step in writing a page */
+
+	sequence_reset(docptr);
+	writew(DOCG4_SEQ_PAGEWRITE, docptr + DOC_FLASHSEQUENCE);
+	writew(DOCG4_CMD_PAGEWRITE, docptr + DOC_FLASHCOMMAND);
+	write_nop(docptr);
+	write_addr(docptr, docg4_addr);
+	write_nop(docptr);
+	write_nop(docptr);
+	poll_status(docptr);
+}
+
+static uint32_t mtd_to_docg4_address(int page, int column)
+{
+	/*
+	 * Convert mtd address to format used by the device, 32 bit packed.
+	 *
+	 * Some notes on G4 addressing... The M-Sys documentation on this device
+	 * claims that pages are 2K in length, and indeed, the format of the
+	 * address used by the device reflects that.  But within each page are
+	 * four 512 byte "sub-pages", each with its own oob data that is
+	 * read/written immediately after the 512 bytes of page data.  This oob
+	 * data contains the ecc bytes for the preceeding 512 bytes.
+	 *
+	 * Rather than tell the mtd nand infrastructure that page size is 2k,
+	 * with four sub-pages each, we engage in a little subterfuge and tell
+	 * the infrastructure code that pages are 512 bytes in size.  This is
+	 * done because during the course of reverse-engineering the device, I
+	 * never observed an instance where an entire 2K "page" was read or
+	 * written as a unit.  Each "sub-page" is always addressed individually,
+	 * its data read/written, and ecc handled before the next "sub-page" is
+	 * addressed.
+	 *
+	 * This requires us to convert addresses passed by the mtd nand
+	 * infrastructure code to those used by the device.
+	 *
+	 * The address that is written to the device consists of four bytes: the
+	 * first two are the 2k page number, and the second is the index into
+	 * the page.  The index is in terms of 16-bit half-words and includes
+	 * the preceeding oob data, so e.g., the index into the second
+	 * "sub-page" is 0x108, and the full device address of the start of mtd
+	 * page 0x201 is 0x00800108.
+	 */
+	int g4_page = page / 4;	                      /* device's 2K page */
+	int g4_index = (page % 4) * 0x108 + column/2; /* offset into page */
+	return (g4_page << 16) | g4_index;	      /* pack */
+}
+
+static void docg4_command(struct mtd_info *mtd, unsigned command, int column,
+			  int page_addr)
+{
+	/* handle standard nand commands */
+
+	struct nand_chip *nand = mtd->priv;
+	struct docg4_priv *doc = nand->priv;
+	uint32_t g4_addr = mtd_to_docg4_address(page_addr, column);
+
+	MTDDEBUG(MTD_DEBUG_LEVEL3, "%s %x, page_addr=%x, column=%x\n",
+	    __func__, command, page_addr, column);
+
+	/*
+	 * Save the command and its arguments.  This enables emulation of
+	 * standard flash devices, and also some optimizations.
+	 */
+	doc->last_command.command = command;
+	doc->last_command.column = column;
+	doc->last_command.page = page_addr;
+
+	switch (command) {
+	case NAND_CMD_RESET:
+		reset(CONFIG_SYS_NAND_BASE);
+		break;
+
+	case NAND_CMD_READ0:
+		read_page_prologue(CONFIG_SYS_NAND_BASE, g4_addr);
+		break;
+
+	case NAND_CMD_STATUS:
+		/* next call to read_byte() will expect a status */
+		break;
+
+	case NAND_CMD_SEQIN:
+		write_page_prologue(CONFIG_SYS_NAND_BASE, g4_addr);
+
+		/* hack for deferred write of oob bytes */
+		if (doc->oob_page == page_addr)
+			memcpy(nand->oob_poi, doc->oob_buf, 16);
+		break;
+
+	case NAND_CMD_PAGEPROG:
+		pageprog(mtd);
+		break;
+
+	/* we don't expect these, based on review of nand_base.c */
+	case NAND_CMD_READOOB:
+	case NAND_CMD_READID:
+	case NAND_CMD_ERASE1:
+	case NAND_CMD_ERASE2:
+		printf("docg4_command: unexpected nand command 0x%x\n",
+		       command);
+		break;
+	}
+}
+
+static void docg4_read_buf(struct mtd_info *mtd, uint8_t *buf, int len)
+{
+	int i;
+	struct nand_chip *nand = mtd->priv;
+	uint16_t *p = (uint16_t *)buf;
+	len >>= 1;
+
+	for (i = 0; i < len; i++)
+		p[i] = readw(nand->IO_ADDR_R);
+}
+
+static int docg4_read_oob(struct mtd_info *mtd, struct nand_chip *nand,
+			  int page, int sndcmd)
+{
+	struct docg4_priv *doc = nand->priv;
+	void __iomem *docptr = CONFIG_SYS_NAND_BASE;
+	uint16_t status;
+
+	MTDDEBUG(MTD_DEBUG_LEVEL3, "%s: page %x\n", __func__, page);
+
+	/*
+	 * Oob bytes are read as part of a normal page read.  If the previous
+	 * nand command was a read of the page whose oob is now being read, just
+	 * copy the oob bytes that we saved in a local buffer and avoid a
+	 * separate oob read.
+	 */
+	if (doc->last_command.command == NAND_CMD_READ0 &&
+	    doc->last_command.page == page) {
+		memcpy(nand->oob_poi, doc->oob_buf, 16);
+		return 0;
+	}
+
+	/*
+	 * Separate read of oob data only.
+	 */
+	docg4_command(mtd, NAND_CMD_READ0, nand->ecc.size, page);
+
+	writew(DOC_ECCCONF0_READ_MODE | DOCG4_OOB_SIZE, docptr + DOC_ECCCONF0);
+	write_nop(docptr);
+	write_nop(docptr);
+	write_nop(docptr);
+	write_nop(docptr);
+	write_nop(docptr);
+
+	/* the 1st byte from the I/O reg is a status; the rest is oob data */
+	status = readw(docptr + DOC_IOSPACE_DATA);
+	if (status & DOCG4_READ_ERROR) {
+		printf("docg4_read_oob failed: status = 0x%02x\n", status);
+		return -EIO;
+	}
+
+	MTDDEBUG(MTD_DEBUG_LEVEL3, "%s: status = 0x%x\n", __func__, status);
+
+	docg4_read_buf(mtd, nand->oob_poi, 16);
+
+	write_nop(docptr);
+	write_nop(docptr);
+	write_nop(docptr);
+	writew(0, docptr + DOC_DATAEND);
+	write_nop(docptr);
+
+	return 0;
+}
+
+static int docg4_write_oob(struct mtd_info *mtd, struct nand_chip *nand,
+			   int page)
+{
+	/*
+	 * Writing oob-only is not really supported, because MLC nand must write
+	 * oob bytes at the same time as page data.  Nonetheless, we save the
+	 * oob buffer contents here, and then write it along with the page data
+	 * if the same page is subsequently written.  This allows user space
+	 * utilities that write the oob data prior to the page data to work
+	 * (e.g., nandwrite).  The disdvantage is that, if the intention was to
+	 * write oob only, the operation is quietly ignored.  Also, oob can get
+	 * corrupted if two concurrent processes are running nandwrite.
+	 */
+
+	/* note that bytes 7..14 are hw generated hamming/ecc and overwritten */
+	struct docg4_priv *doc = nand->priv;
+	doc->oob_page = page;
+	memcpy(doc->oob_buf, nand->oob_poi, 16);
+	return 0;
+}
+
+static int docg4_block_neverbad(struct mtd_info *mtd, loff_t ofs, int getchip)
+{
+	/* only called when module_param ignore_badblocks is set */
+	return 0;
+}
+
+static void docg4_write_buf16(struct mtd_info *mtd, const uint8_t *buf, int len)
+{
+	int i;
+	struct nand_chip *nand = mtd->priv;
+	uint16_t *p = (uint16_t *)buf;
+	len >>= 1;
+
+	for (i = 0; i < len; i++)
+		writew(p[i], nand->IO_ADDR_W);
+}
+
+static void write_page(struct mtd_info *mtd, struct nand_chip *nand,
+		       const uint8_t *buf, int use_ecc)
+{
+	void __iomem *docptr = CONFIG_SYS_NAND_BASE;
+	uint8_t ecc_buf[8];
+
+	writew(DOC_ECCCONF0_ECC_ENABLE |
+	       DOC_ECCCONF0_UNKNOWN |
+	       DOCG4_BCH_SIZE,
+	       docptr + DOC_ECCCONF0);
+	write_nop(docptr);
+
+	/* write the page data */
+	docg4_write_buf16(mtd, buf, DOCG4_PAGE_SIZE);
+
+	/* oob bytes 0 through 5 are written to I/O reg */
+	docg4_write_buf16(mtd, nand->oob_poi, 6);
+
+	/* oob byte 6 written to a separate reg */
+	writew(nand->oob_poi[6], docptr + DOCG4_OOB_6_7);
+
+	write_nop(docptr);
+	write_nop(docptr);
+
+	/* write hw-generated ecc bytes to oob */
+	if (likely(use_ecc)) {
+		/* oob byte 7 is hamming code */
+		uint8_t hamming = readb(docptr + DOC_HAMMINGPARITY);
+		hamming = readb(docptr + DOC_HAMMINGPARITY); /* 2nd read */
+		writew(hamming, docptr + DOCG4_OOB_6_7);
+		write_nop(docptr);
+
+		/* read the 7 bch bytes from ecc regs */
+		read_hw_ecc(docptr, ecc_buf);
+		ecc_buf[7] = 0;         /* clear the "page written" flag */
+	}
+
+	/* write user-supplied bytes to oob */
+	else {
+		writew(nand->oob_poi[7], docptr + DOCG4_OOB_6_7);
+		write_nop(docptr);
+		memcpy(ecc_buf, &nand->oob_poi[8], 8);
+	}
+
+	docg4_write_buf16(mtd, ecc_buf, 8);
+	write_nop(docptr);
+	write_nop(docptr);
+	writew(0, docptr + DOC_DATAEND);
+	write_nop(docptr);
+}
+
+static void docg4_write_page_raw(struct mtd_info *mtd, struct nand_chip *nand,
+				 const uint8_t *buf)
+{
+	return write_page(mtd, nand, buf, 0);
+}
+
+static void docg4_write_page(struct mtd_info *mtd, struct nand_chip *nand,
+			     const uint8_t *buf)
+{
+	return write_page(mtd, nand, buf, 1);
+}
+
+static int read_page(struct mtd_info *mtd, struct nand_chip *nand,
+		     uint8_t *buf, int page, int use_ecc)
+{
+	struct docg4_priv *doc = nand->priv;
+	void __iomem *docptr = CONFIG_SYS_NAND_BASE;
+	uint16_t status, edc_err, *buf16;
+
+	writew(DOC_ECCCONF0_READ_MODE |
+	       DOC_ECCCONF0_ECC_ENABLE |
+	       DOC_ECCCONF0_UNKNOWN |
+	       DOCG4_BCH_SIZE,
+	       docptr + DOC_ECCCONF0);
+	write_nop(docptr);
+	write_nop(docptr);
+	write_nop(docptr);
+	write_nop(docptr);
+	write_nop(docptr);
+
+	/* the 1st byte from the I/O reg is a status; the rest is page data */
+	status = readw(docptr + DOC_IOSPACE_DATA);
+	if (status & DOCG4_READ_ERROR) {
+		printf("docg4_read_page: bad status: 0x%02x\n", status);
+		writew(0, docptr + DOC_DATAEND);
+		return -EIO;
+	}
+
+	docg4_read_buf(mtd, buf, DOCG4_PAGE_SIZE); /* read the page data */
+
+	/* first 14 oob bytes read from I/O reg */
+	docg4_read_buf(mtd, nand->oob_poi, 14);
+
+	/* last 2 read from another reg */
+	buf16 = (uint16_t *)(nand->oob_poi + 14);
+	*buf16 = readw(docptr + DOCG4_MYSTERY_REG);
+
+	/*
+	 * Diskonchips read oob immediately after a page read.  Mtd
+	 * infrastructure issues a separate command for reading oob after the
+	 * page is read.  So we save the oob bytes in a local buffer and just
+	 * copy it if the next command reads oob from the same page.
+	 */
+	memcpy(doc->oob_buf, nand->oob_poi, 16);
+
+	write_nop(docptr);
+
+	if (likely(use_ecc)) {
+		/* read the register that tells us if bitflip(s) detected  */
+		edc_err = readw(docptr + DOC_ECCCONF1);
+		edc_err = readw(docptr + DOC_ECCCONF1);
+
+		/* If bitflips are reported, attempt to correct with ecc */
+		if (edc_err & DOC_ECCCONF1_BCH_SYNDROM_ERR) {
+			int bits_corrected = correct_data(mtd, buf, page);
+			if (bits_corrected == -EBADMSG)
+				mtd->ecc_stats.failed++;
+			else
+				mtd->ecc_stats.corrected += bits_corrected;
+		}
+	}
+
+	writew(0, docptr + DOC_DATAEND);
+	return 0;
+}
+
+
+static int docg4_read_page_raw(struct mtd_info *mtd, struct nand_chip *nand,
+			       uint8_t *buf, int page)
+{
+	return read_page(mtd, nand, buf, page, 0);
+}
+
+static int docg4_read_page(struct mtd_info *mtd, struct nand_chip *nand,
+			   uint8_t *buf, int page)
+{
+	return read_page(mtd, nand, buf, page, 1);
+}
+
+static void docg4_erase_block(struct mtd_info *mtd, int page)
+{
+	struct nand_chip *nand = mtd->priv;
+	struct docg4_priv *doc = nand->priv;
+	void __iomem *docptr = CONFIG_SYS_NAND_BASE;
+	uint16_t g4_page;
+
+	MTDDEBUG(MTD_DEBUG_LEVEL3, "%s: page %04x\n", __func__, page);
+
+	sequence_reset(docptr);
+
+	writew(DOCG4_SEQ_BLOCKERASE, docptr + DOC_FLASHSEQUENCE);
+	writew(DOC_CMD_PROG_BLOCK_ADDR, docptr + DOC_FLASHCOMMAND);
+	write_nop(docptr);
+
+	/* only 2 bytes of address are written to specify erase block */
+	g4_page = (uint16_t)(page / 4);  /* to g4's 2k page addressing */
+	writeb(g4_page & 0xff, docptr + DOC_FLASHADDRESS);
+	g4_page >>= 8;
+	writeb(g4_page & 0xff, docptr + DOC_FLASHADDRESS);
+	write_nop(docptr);
+
+	/* start the erasure */
+	writew(DOC_CMD_ERASECYCLE2, docptr + DOC_FLASHCOMMAND);
+	write_nop(docptr);
+	write_nop(docptr);
+
+	poll_status(docptr);
+	writew(DOCG4_SEQ_FLUSH, docptr + DOC_FLASHSEQUENCE);
+	writew(DOCG4_CMD_FLUSH, docptr + DOC_FLASHCOMMAND);
+	writew(DOC_ECCCONF0_READ_MODE | 4, docptr + DOC_ECCCONF0);
+	write_nop(docptr);
+	write_nop(docptr);
+	write_nop(docptr);
+	write_nop(docptr);
+	write_nop(docptr);
+
+	read_progstatus(doc, docptr);
+
+	writew(0, docptr + DOC_DATAEND);
+	write_nop(docptr);
+	poll_status(docptr);
+	write_nop(docptr);
+}
+
+static int read_factory_bbt(struct mtd_info *mtd)
+{
+	/*
+	 * The device contains a read-only factory bad block table.  Read it and
+	 * update the memory-based bbt accordingly.
+	 */
+
+	struct nand_chip *nand = mtd->priv;
+	uint32_t g4_addr = mtd_to_docg4_address(DOCG4_FACTORY_BBT_PAGE, 0);
+	uint8_t *buf;
+	int i, block, status;
+
+	buf = kzalloc(DOCG4_PAGE_SIZE, GFP_KERNEL);
+	if (buf == NULL)
+		return -ENOMEM;
+
+	read_page_prologue(CONFIG_SYS_NAND_BASE, g4_addr);
+	status = docg4_read_page(mtd, nand, buf, DOCG4_FACTORY_BBT_PAGE);
+	if (status)
+		goto exit;
+
+	/*
+	 * If no memory-based bbt was created, exit.  This will happen if module
+	 * parameter ignore_badblocks is set.  Then why even call this function?
+	 * For an unknown reason, block erase always fails if it's the first
+	 * operation after device power-up.  The above read ensures it never is.
+	 * Ugly, I know.
+	 */
+	if (nand->bbt == NULL)  /* no memory-based bbt */
+		goto exit;
+
+	/*
+	 * Parse factory bbt and update memory-based bbt.  Factory bbt format is
+	 * simple: one bit per block, block numbers increase left to right (msb
+	 * to lsb).  Bit clear means bad block.
+	 */
+	for (i = block = 0; block < DOCG4_NUMBLOCKS; block += 8, i++) {
+		int bitnum;
+		uint8_t mask;
+		for (bitnum = 0, mask = 0x80;
+		     bitnum < 8; bitnum++, mask >>= 1) {
+			if (!(buf[i] & mask)) {
+				int badblock = block + bitnum;
+				nand->bbt[badblock / 4] |=
+					0x03 << ((badblock % 4) * 2);
+				mtd->ecc_stats.badblocks++;
+				printf("factory-marked bad block: %d\n",
+				       badblock);
+			}
+		}
+	}
+ exit:
+	kfree(buf);
+	return status;
+}
+
+static int docg4_block_markbad(struct mtd_info *mtd, loff_t ofs)
+{
+	/*
+	 * Mark a block as bad.  Bad blocks are marked in the oob area of the
+	 * first page of the block.  The default scan_bbt() in the nand
+	 * infrastructure code works fine for building the memory-based bbt
+	 * during initialization, as does the nand infrastructure function that
+	 * checks if a block is bad by reading the bbt.  This function replaces
+	 * the nand default because writes to oob-only are not supported.
+	 */
+
+	int ret, i;
+	uint8_t *buf;
+	struct nand_chip *nand = mtd->priv;
+	struct nand_bbt_descr *bbtd = nand->badblock_pattern;
+	int block = (int)(ofs >> nand->bbt_erase_shift);
+	int page = (int)(ofs >> nand->page_shift);
+	uint32_t g4_addr = mtd_to_docg4_address(page, 0);
+
+	MTDDEBUG(MTD_DEBUG_LEVEL3, "%s: %08llx\n", __func__, ofs);
+
+	if (unlikely(ofs & (DOCG4_BLOCK_SIZE - 1)))
+		printf("%s: ofs %llx not start of block!\n",
+		       __func__, ofs);
+
+	/* allocate blank buffer for page data */
+	buf = kzalloc(DOCG4_PAGE_SIZE, GFP_KERNEL);
+	if (buf == NULL)
+		return -ENOMEM;
+
+	/* update bbt in memory */
+	nand->bbt[block / 4] |= 0x01 << ((block & 0x03) * 2);
+
+	/* write bit-wise negation of pattern to oob buffer */
+	memset(nand->oob_poi, 0xff, mtd->oobsize);
+	for (i = 0; i < bbtd->len; i++)
+		nand->oob_poi[bbtd->offs + i] = ~bbtd->pattern[i];
+
+	/* write first page of block */
+	write_page_prologue(CONFIG_SYS_NAND_BASE, g4_addr);
+	docg4_write_page(mtd, nand, buf);
+	ret = pageprog(mtd);
+	if (!ret)
+		mtd->ecc_stats.badblocks++;
+
+	kfree(buf);
+
+	return ret;
+}
+
+static uint8_t docg4_read_byte(struct mtd_info *mtd)
+{
+	struct nand_chip *nand = mtd->priv;
+	struct docg4_priv *doc = nand->priv;
+
+	MTDDEBUG(MTD_DEBUG_LEVEL3, "%s\n", __func__);
+
+	if (doc->last_command.command == NAND_CMD_STATUS) {
+		int status;
+
+		/*
+		 * Previous nand command was status request, so nand
+		 * infrastructure code expects to read the status here.  If an
+		 * error occurred in a previous operation, report it.
+		 */
+		doc->last_command.command = 0;
+
+		if (doc->status) {
+			status = doc->status;
+			doc->status = 0;
+		}
+
+		/* why is NAND_STATUS_WP inverse logic?? */
+		else
+			status = NAND_STATUS_WP | NAND_STATUS_READY;
+
+		return status;
+	}
+
+	printf("unexpectd call to read_byte()\n");
+
+	return 0;
+}
+
+static int docg4_wait(struct mtd_info *mtd, struct nand_chip *nand)
+{
+	struct docg4_priv *doc = nand->priv;
+	int status = NAND_STATUS_WP;       /* inverse logic?? */
+	MTDDEBUG(MTD_DEBUG_LEVEL3, "%s...\n", __func__);
+
+	/* report any previously unreported error */
+	if (doc->status) {
+		status |= doc->status;
+		doc->status = 0;
+		return status;
+	}
+
+	status |= poll_status(CONFIG_SYS_NAND_BASE);
+	return status;
+}
+
+int docg4_nand_init(struct mtd_info *mtd, struct nand_chip *nand, int devnum)
+{
+	uint16_t id1, id2;
+	struct docg4_priv *docg4;
+	int retval;
+
+	docg4 = kzalloc(sizeof(*docg4), GFP_KERNEL);
+	if (!docg4)
+		return -1;
+
+	mtd->priv = nand;
+	nand->priv = docg4;
+
+	/* These must be initialized here because the docg4 is non-standard
+	 * and doesn't produce an id that the nand code can use to look up
+	 * these values (nand_scan_ident() not called).
+	 */
+	mtd->size = DOCG4_CHIP_SIZE;
+	mtd->name = "Msys_Diskonchip_G4";
+	mtd->writesize = DOCG4_PAGE_SIZE;
+	mtd->erasesize = DOCG4_BLOCK_SIZE;
+	mtd->oobsize = DOCG4_OOB_SIZE;
+
+	nand->IO_ADDR_R =
+		(void __iomem *)CONFIG_SYS_NAND_BASE + DOC_IOSPACE_DATA;
+	nand->IO_ADDR_W = nand->IO_ADDR_R;
+	nand->chipsize = DOCG4_CHIP_SIZE;
+	nand->chip_shift = DOCG4_CHIP_SHIFT;
+	nand->bbt_erase_shift = DOCG4_ERASE_SHIFT;
+	nand->phys_erase_shift = DOCG4_ERASE_SHIFT;
+	nand->chip_delay = 20;
+	nand->page_shift = DOCG4_PAGE_SHIFT;
+	nand->pagemask = 0x3ffff;
+	nand->badblockpos = NAND_LARGE_BADBLOCK_POS;
+	nand->badblockbits = 8;
+	nand->ecc.layout = &docg4_oobinfo;
+	nand->ecc.mode = NAND_ECC_HW_SYNDROME;
+	nand->ecc.size = DOCG4_PAGE_SIZE;
+	nand->ecc.prepad = 8;
+	nand->ecc.bytes	= 8;
+	nand->options =
+		NAND_BUSWIDTH_16 | NAND_NO_SUBPAGE_WRITE | NAND_NO_AUTOINCR;
+	nand->controller = &nand->hwcontrol;
+
+	/* methods */
+	nand->cmdfunc = docg4_command;
+	nand->waitfunc = docg4_wait;
+	nand->select_chip = docg4_select_chip;
+	nand->read_byte = docg4_read_byte;
+	nand->block_markbad = docg4_block_markbad;
+	nand->read_buf = docg4_read_buf;
+	nand->write_buf = docg4_write_buf16;
+	nand->scan_bbt = nand_default_bbt;
+	nand->erase_cmd = docg4_erase_block;
+	nand->ecc.read_page = docg4_read_page;
+	nand->ecc.write_page = docg4_write_page;
+	nand->ecc.read_page_raw = docg4_read_page_raw;
+	nand->ecc.write_page_raw = docg4_write_page_raw;
+	nand->ecc.read_oob = docg4_read_oob;
+	nand->ecc.write_oob = docg4_write_oob;
+
+	/*
+	 * The way the nand infrastructure code is written, a memory-based bbt
+	 * is not created if NAND_SKIP_BBTSCAN is set.  With no memory bbt,
+	 * nand->block_bad() is used.  So when ignoring bad blocks, we skip the
+	 * scan and define a dummy block_bad() which always returns 0.
+	 */
+	if (ignore_badblocks) {
+		nand->options |= NAND_SKIP_BBTSCAN;
+		nand->block_bad	= docg4_block_neverbad;
+	}
+
+	reset(CONFIG_SYS_NAND_BASE);
+
+	/* check for presence of g4 chip by reading id registers */
+	id1 = readw(CONFIG_SYS_NAND_BASE + DOC_CHIPID);
+	id1 = readw(CONFIG_SYS_NAND_BASE + DOCG4_MYSTERY_REG);
+	id2 = readw(CONFIG_SYS_NAND_BASE + DOC_CHIPID_INV);
+	id2 = readw(CONFIG_SYS_NAND_BASE + DOCG4_MYSTERY_REG);
+	if (id1 != DOCG4_IDREG1_VALUE || id2 != DOCG4_IDREG2_VALUE)
+		return -1;
+
+	/* initialize bch algorithm */
+	docg4->bch = init_bch(DOCG4_M, DOCG4_T, DOCG4_PRIMITIVE_POLY);
+	if (docg4->bch == NULL)
+		return -1;
+
+	retval = nand_scan_tail(mtd);
+	if (retval)
+		return -1;
+
+	/*
+	 * Scan for bad blocks and create bbt here, then add the factory-marked
+	 * bad blocks to the bbt.
+	 */
+	nand->scan_bbt(mtd);
+	nand->options |= NAND_BBT_SCANNED;
+	retval = read_factory_bbt(mtd);
+	if (retval)
+		return -1;
+
+	retval = nand_register(devnum);
+	if (retval)
+		return -1;
+
+	return 0;
+}