mtd: nand: add support for diskonchip G4 nand flash device

This patch adds a driver for the M-Sys / Sandisk diskonchip G4 nand flash found
in various smartphones and PDAs, among them the Palm Treo680, HTC Prophet and
Wizard, Toshiba Portege G900, Asus P526, and O2 XDA Zinc.  It was tested on the
Treo 680, but should work generically.

Since v3, this patch adds power management functions, a scan of the factory bad
block table during initialization, several fixes, and more extensive testing.
Also, the platform data header file, which only contained partitioning
information, was removed.  Command-line partitioning can be used, at least until
an mtd parser is written for the saftl format with which these chips are
shipped.

Signed-off-by: Mike Dunn <mikedunn@newsguy.com>
Reviewed-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 1378 insertions, 0 deletions

diff --git a/drivers/mtd/nand/docg4.c b/drivers/mtd/nand/docg4.c
new file mode 100644
index 000000000000..baae75b37d7e
--- /dev/null
+++ b/drivers/mtd/nand/docg4.c
@@ -0,0 +1,1378 @@
+/*
+ *  Copyright © 2012 Mike Dunn <mikedunn@newsguy.com>
+ *
+ * mtd nand driver for M-Systems DiskOnChip G4
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * 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 <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/string.h>
+#include <linux/sched.h>
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/export.h>
+#include <linux/platform_device.h>
+#include <linux/io.h>
+#include <linux/bitops.h>
+#include <linux/mtd/partitions.h>
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/nand.h>
+#include <linux/bch.h>
+#include <linux/bitrev.h>
+
+/*
+ * You'll want to ignore badblocks if you're reading a partition that contains
+ * data written by the TrueFFS library (i.e., by PalmOS, Windows, etc), since
+ * it does not use mtd nand's method for marking bad blocks (using oob area).
+ * This will also skip the check of the "page written" flag.
+ */
+static bool ignore_badblocks;
+module_param(ignore_badblocks, bool, 0);
+MODULE_PARM_DESC(ignore_badblocks, "no badblock checking performed");
+
+struct docg4_priv {
+	struct mtd_info	*mtd;
+	struct device *dev;
+	void __iomem *virtadr;
+	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;
+};
+
+/*
+ * Defines prefixed with DOCG4 are unique to the diskonchip G4.  All others are
+ * shared with other diskonchip devices (P3, G3 at least).
+ *
+ * Functions with names prefixed with docg4_ are mtd / nand interface functions
+ * (though they may also be called internally).  All others are internal.
+ */
+
+#define DOC_IOSPACE_DATA		0x0800
+
+/* register offsets */
+#define DOC_CHIPID			0x1000
+#define DOC_DEVICESELECT		0x100a
+#define DOC_ASICMODE			0x100c
+#define DOC_DATAEND			0x101e
+#define DOC_NOP				0x103e
+
+#define DOC_FLASHSEQUENCE		0x1032
+#define DOC_FLASHCOMMAND		0x1034
+#define DOC_FLASHADDRESS		0x1036
+#define DOC_FLASHCONTROL		0x1038
+#define DOC_ECCCONF0			0x1040
+#define DOC_ECCCONF1			0x1042
+#define DOC_HAMMINGPARITY		0x1046
+#define DOC_BCH_SYNDROM(idx)		(0x1048 + idx)
+
+#define DOC_ASICMODECONFIRM		0x1072
+#define DOC_CHIPID_INV			0x1074
+#define DOC_POWERMODE			0x107c
+
+#define DOCG4_MYSTERY_REG		0x1050
+
+/* apparently used only to write oob bytes 6 and 7 */
+#define DOCG4_OOB_6_7			0x1052
+
+/* DOC_FLASHSEQUENCE register commands */
+#define DOC_SEQ_RESET			0x00
+#define DOCG4_SEQ_PAGE_READ		0x03
+#define DOCG4_SEQ_FLUSH			0x29
+#define DOCG4_SEQ_PAGEWRITE		0x16
+#define DOCG4_SEQ_PAGEPROG		0x1e
+#define DOCG4_SEQ_BLOCKERASE		0x24
+
+/* DOC_FLASHCOMMAND register commands */
+#define DOCG4_CMD_PAGE_READ             0x00
+#define DOC_CMD_ERASECYCLE2		0xd0
+#define DOCG4_CMD_FLUSH                 0x70
+#define DOCG4_CMD_READ2                 0x30
+#define DOC_CMD_PROG_BLOCK_ADDR		0x60
+#define DOCG4_CMD_PAGEWRITE		0x80
+#define DOC_CMD_PROG_CYCLE2		0x10
+#define DOC_CMD_RESET			0xff
+
+/* DOC_POWERMODE register bits */
+#define DOC_POWERDOWN_READY		0x80
+
+/* DOC_FLASHCONTROL register bits */
+#define DOC_CTRL_CE			0x10
+#define DOC_CTRL_UNKNOWN		0x40
+#define DOC_CTRL_FLASHREADY		0x01
+
+/* DOC_ECCCONF0 register bits */
+#define DOC_ECCCONF0_READ_MODE		0x8000
+#define DOC_ECCCONF0_UNKNOWN		0x2000
+#define DOC_ECCCONF0_ECC_ENABLE	        0x1000
+#define DOC_ECCCONF0_DATA_BYTES_MASK	0x07ff
+
+/* DOC_ECCCONF1 register bits */
+#define DOC_ECCCONF1_BCH_SYNDROM_ERR	0x80
+#define DOC_ECCCONF1_ECC_ENABLE         0x07
+#define DOC_ECCCONF1_PAGE_IS_WRITTEN	0x20
+
+/* DOC_ASICMODE register bits */
+#define DOC_ASICMODE_RESET		0x00
+#define DOC_ASICMODE_NORMAL		0x01
+#define DOC_ASICMODE_POWERDOWN		0x02
+#define DOC_ASICMODE_MDWREN		0x04
+#define DOC_ASICMODE_BDETCT_RESET	0x08
+#define DOC_ASICMODE_RSTIN_RESET	0x10
+#define DOC_ASICMODE_RAM_WE		0x20
+
+/* good status values read after read/write/erase operations */
+#define DOCG4_PROGSTATUS_GOOD          0x51
+#define DOCG4_PROGSTATUS_GOOD_2        0xe0
+
+/*
+ * On read operations (page and oob-only), the first byte read from I/O reg is a
+ * status.  On error, it reads 0x73; otherwise, it reads either 0x71 (first read
+ * after reset only) or 0x51, so bit 1 is presumed to be an error indicator.
+ */
+#define DOCG4_READ_ERROR           0x02 /* bit 1 indicates read error */
+
+/* anatomy of the device */
+#define DOCG4_CHIP_SIZE        0x8000000
+#define DOCG4_PAGE_SIZE        0x200
+#define DOCG4_PAGES_PER_BLOCK  0x200
+#define DOCG4_BLOCK_SIZE       (DOCG4_PAGES_PER_BLOCK * DOCG4_PAGE_SIZE)
+#define DOCG4_NUMBLOCKS        (DOCG4_CHIP_SIZE / DOCG4_BLOCK_SIZE)
+#define DOCG4_OOB_SIZE         0x10
+#define DOCG4_CHIP_SHIFT       27    /* log_2(DOCG4_CHIP_SIZE) */
+#define DOCG4_PAGE_SHIFT       9     /* log_2(DOCG4_PAGE_SIZE) */
+#define DOCG4_ERASE_SHIFT      18    /* log_2(DOCG4_BLOCK_SIZE) */
+
+/* all but the last byte is included in ecc calculation */
+#define DOCG4_BCH_SIZE         (DOCG4_PAGE_SIZE + DOCG4_OOB_SIZE - 1)
+
+#define DOCG4_USERDATA_LEN     520 /* 512 byte page plus 8 oob avail to user */
+
+/* expected values from the ID registers */
+#define DOCG4_IDREG1_VALUE     0x0400
+#define DOCG4_IDREG2_VALUE     0xfbff
+
+/* primitive polynomial used to build the Galois field used by hw ecc gen */
+#define DOCG4_PRIMITIVE_POLY   0x4443
+
+#define DOCG4_M                14  /* Galois field is of order 2^14 */
+#define DOCG4_T                4   /* BCH alg corrects up to 4 bit errors */
+
+#define DOCG4_FACTORY_BBT_PAGE 16 /* page where read-only factory bbt lives */
+
+/*
+ * 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} }
+};
+
+/*
+ * 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 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 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 int poll_status(struct docg4_priv *doc)
+{
+	/*
+	 * 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.
+	 */
+
+	uint16_t flash_status;
+	unsigned int timeo;
+	void __iomem *docptr = doc->virtadr;
+
+	dev_dbg(doc->dev, "%s...\n", __func__);
+
+	/* hardware quirk requires reading twice initially */
+	flash_status = readw(docptr + DOC_FLASHCONTROL);
+
+	timeo = 1000;
+	do {
+		cpu_relax();
+		flash_status = readb(docptr + DOC_FLASHCONTROL);
+	} while (!(flash_status & DOC_CTRL_FLASHREADY) && --timeo);
+
+
+	if (!timeo) {
+		dev_err(doc->dev, "%s: timed out!\n", __func__);
+		return NAND_STATUS_FAIL;
+	}
+
+	if (unlikely(timeo < 50))
+		dev_warn(doc->dev, "%s: nearly timed out; %d remaining\n",
+			 __func__, timeo);
+
+	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?? */
+	dev_dbg(doc->dev, "%s...\n", __func__);
+
+	/* report any previously unreported error */
+	if (doc->status) {
+		status |= doc->status;
+		doc->status = 0;
+		return status;
+	}
+
+	status |= poll_status(doc);
+	return status;
+}
+
+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.
+	 */
+	struct nand_chip *nand = mtd->priv;
+	struct docg4_priv *doc = nand->priv;
+	void __iomem *docptr = doc->virtadr;
+
+	dev_dbg(doc->dev, "%s: chip %d\n", __func__, chip);
+
+	if (chip < 0)
+		return;		/* deselected */
+
+	if (chip > 0)
+		dev_warn(doc->dev, "multiple floors currently unsupported\n");
+
+	writew(0, docptr + DOC_DEVICESELECT);
+}
+
+static void reset(struct mtd_info *mtd)
+{
+	/* full device reset */
+
+	struct nand_chip *nand = mtd->priv;
+	struct docg4_priv *doc = nand->priv;
+	void __iomem *docptr = doc->virtadr;
+
+	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(doc);
+}
+
+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 = doc->virtadr;
+	int i, numerrs, 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 == false) {
+
+		/*
+		 * 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_each_set_bit(bit, &written_flag, 8)
+				numsetbits++;
+			if (numsetbits > 4) { /* assume blank */
+				dev_warn(doc->dev,
+					 "error(s) 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) {
+		dev_warn(doc->dev, "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);
+	}
+
+	dev_notice(doc->dev, "%d error(s) corrected at offset %08x\n",
+		   numerrs, page * DOCG4_PAGE_SIZE);
+
+	return numerrs;
+}
+
+static uint8_t docg4_read_byte(struct mtd_info *mtd)
+{
+	struct nand_chip *nand = mtd->priv;
+	struct docg4_priv *doc = nand->priv;
+
+	dev_dbg(doc->dev, "%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;
+	}
+
+	dev_warn(doc->dev, "unexpectd call to read_byte()\n");
+
+	return 0;
+}
+
+static void write_addr(struct docg4_priv *doc, uint32_t docg4_addr)
+{
+	/* write the four address bytes packed in docg4_addr to the device */
+
+	void __iomem *docptr = doc->virtadr;
+	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);
+}
+
+static int read_progstatus(struct docg4_priv *doc)
+{
+	/*
+	 * 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.
+	 */
+	void __iomem *docptr = doc->virtadr;
+
+	/* 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);
+
+	dev_dbg(doc->dev, "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;
+		dev_warn(doc->dev, "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 = doc->virtadr;
+	int retval = 0;
+
+	dev_dbg(doc->dev, "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(doc);
+
+	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);
+	writew(0, docptr + DOC_DATAEND);
+	write_nop(docptr);
+	poll_status(doc);
+	write_nop(docptr);
+
+	return retval;
+}
+
+static void sequence_reset(struct mtd_info *mtd)
+{
+	/* common starting sequence for all operations */
+
+	struct nand_chip *nand = mtd->priv;
+	struct docg4_priv *doc = nand->priv;
+	void __iomem *docptr = doc->virtadr;
+
+	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(doc);
+	write_nop(docptr);
+}
+
+static void read_page_prologue(struct mtd_info *mtd, uint32_t docg4_addr)
+{
+	/* first step in reading a page */
+
+	struct nand_chip *nand = mtd->priv;
+	struct docg4_priv *doc = nand->priv;
+	void __iomem *docptr = doc->virtadr;
+
+	dev_dbg(doc->dev,
+	      "docg4: %s: g4 page %08x\n", __func__, docg4_addr);
+
+	sequence_reset(mtd);
+
+	writew(DOCG4_SEQ_PAGE_READ, docptr + DOC_FLASHSEQUENCE);
+	writew(DOCG4_CMD_PAGE_READ, docptr + DOC_FLASHCOMMAND);
+	write_nop(docptr);
+
+	write_addr(doc, docg4_addr);
+
+	write_nop(docptr);
+	writew(DOCG4_CMD_READ2, docptr + DOC_FLASHCOMMAND);
+	write_nop(docptr);
+	write_nop(docptr);
+
+	poll_status(doc);
+}
+
+static void write_page_prologue(struct mtd_info *mtd, uint32_t docg4_addr)
+{
+	/* first step in writing a page */
+
+	struct nand_chip *nand = mtd->priv;
+	struct docg4_priv *doc = nand->priv;
+	void __iomem *docptr = doc->virtadr;
+
+	dev_dbg(doc->dev,
+	      "docg4: %s: g4 addr: %x\n", __func__, docg4_addr);
+	sequence_reset(mtd);
+	writew(DOCG4_SEQ_PAGEWRITE, docptr + DOC_FLASHSEQUENCE);
+	writew(DOCG4_CMD_PAGEWRITE, docptr + DOC_FLASHCOMMAND);
+	write_nop(docptr);
+	write_addr(doc, docg4_addr);
+	write_nop(docptr);
+	write_nop(docptr);
+	poll_status(doc);
+}
+
+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);
+
+	dev_dbg(doc->dev, "%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(mtd);
+		break;
+
+	case NAND_CMD_READ0:
+		read_page_prologue(mtd, g4_addr);
+		break;
+
+	case NAND_CMD_STATUS:
+		/* next call to read_byte() will expect a status */
+		break;
+
+	case NAND_CMD_SEQIN:
+		write_page_prologue(mtd, 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:
+		dev_warn(doc->dev, "docg4_command: "
+			 "unexpected nand command 0x%x\n", command);
+		break;
+
+	}
+}
+
+static int read_page(struct mtd_info *mtd, struct nand_chip *nand,
+		     uint8_t *buf, int page, bool use_ecc)
+{
+	struct docg4_priv *doc = nand->priv;
+	void __iomem *docptr = doc->virtadr;
+	uint16_t status, edc_err, *buf16;
+
+	dev_dbg(doc->dev, "%s: page %08x\n", __func__, page);
+
+	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) {
+		dev_err(doc->dev,
+			"docg4_read_page: bad status: 0x%02x\n", status);
+		writew(0, docptr + DOC_DATAEND);
+		return -EIO;
+	}
+
+	dev_dbg(doc->dev, "%s: status = 0x%x\n", __func__, status);
+
+	docg4_read_buf(mtd, buf, DOCG4_PAGE_SIZE); /* read the page data */
+
+	/*
+	 * 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.
+	 */
+
+	/* first 14 oob bytes read from I/O reg */
+	docg4_read_buf(mtd, doc->oob_buf, 14);
+
+	/* last 2 read from another reg */
+	buf16 = (uint16_t *)(doc->oob_buf + 14);
+	*buf16 = readw(docptr + DOCG4_MYSTERY_REG);
+
+	write_nop(docptr);
+
+	if (likely(use_ecc == true)) {
+
+		/* read the register that tells us if bitflip(s) detected  */
+		edc_err = readw(docptr + DOC_ECCCONF1);
+		edc_err = readw(docptr + DOC_ECCCONF1);
+		dev_dbg(doc->dev, "%s: edc_err = 0x%02x\n", __func__, edc_err);
+
+		/* 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, false);
+}
+
+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, true);
+}
+
+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 = doc->virtadr;
+	uint16_t status;
+
+	dev_dbg(doc->dev, "%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) {
+		dev_warn(doc->dev,
+			 "docg4_read_oob failed: status = 0x%02x\n", status);
+		return -EIO;
+	}
+
+	dev_dbg(doc->dev, "%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 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 = doc->virtadr;
+	uint16_t g4_page;
+
+	dev_dbg(doc->dev, "%s: page %04x\n", __func__, page);
+
+	sequence_reset(mtd);
+
+	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);
+
+	usleep_range(500, 1000); /* erasure is long; take a snooze */
+	poll_status(doc);
+	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);
+
+	writew(0, docptr + DOC_DATAEND);
+	write_nop(docptr);
+	poll_status(doc);
+	write_nop(docptr);
+}
+
+static void write_page(struct mtd_info *mtd, struct nand_chip *nand,
+		       const uint8_t *buf, bool use_ecc)
+{
+	struct docg4_priv *doc = nand->priv;
+	void __iomem *docptr = doc->virtadr;
+	uint8_t ecc_buf[8];
+
+	dev_dbg(doc->dev, "%s...\n", __func__);
+
+	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 == true)) {
+		/* 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, false);
+}
+
+static void docg4_write_page(struct mtd_info *mtd, struct nand_chip *nand,
+			     const uint8_t *buf)
+{
+	return write_page(mtd, nand, buf, true);
+}
+
+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 __init 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;
+	struct docg4_priv *doc = nand->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(mtd, 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;
+		unsigned long bits = ~buf[i];
+		for_each_set_bit(bitnum, &bits, 8) {
+			int badblock = block + 7 - bitnum;
+			nand->bbt[badblock / 4] |=
+				0x03 << ((badblock % 4) * 2);
+			mtd->ecc_stats.badblocks++;
+			dev_notice(doc->dev, "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 docg4_priv *doc = nand->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);
+
+	dev_dbg(doc->dev, "%s: %08llx\n", __func__, ofs);
+
+	if (unlikely(ofs & (DOCG4_BLOCK_SIZE - 1)))
+		dev_warn(doc->dev, "%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(mtd, g4_addr);
+	docg4_write_page(mtd, nand, buf);
+	ret = pageprog(mtd);
+	if (!ret)
+		mtd->ecc_stats.badblocks++;
+
+	kfree(buf);
+
+	return ret;
+}
+
+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 int docg4_suspend(struct platform_device *pdev, pm_message_t state)
+{
+	/*
+	 * Put the device into "deep power-down" mode.  Note that CE# must be
+	 * deasserted for this to take effect.  The xscale, e.g., can be
+	 * configured to float this signal when the processor enters power-down,
+	 * and a suitable pull-up ensures its deassertion.
+	 */
+
+	int i;
+	uint8_t pwr_down;
+	struct docg4_priv *doc = platform_get_drvdata(pdev);
+	void __iomem *docptr = doc->virtadr;
+
+	dev_dbg(doc->dev, "%s...\n", __func__);
+
+	/* poll the register that tells us we're ready to go to sleep */
+	for (i = 0; i < 10; i++) {
+		pwr_down = readb(docptr + DOC_POWERMODE);
+		if (pwr_down & DOC_POWERDOWN_READY)
+			break;
+		usleep_range(1000, 4000);
+	}
+
+	if (pwr_down & DOC_POWERDOWN_READY) {
+		dev_err(doc->dev, "suspend failed; "
+			"timeout polling DOC_POWERDOWN_READY\n");
+		return -EIO;
+	}
+
+	writew(DOC_ASICMODE_POWERDOWN | DOC_ASICMODE_MDWREN,
+	       docptr + DOC_ASICMODE);
+	writew(~(DOC_ASICMODE_POWERDOWN | DOC_ASICMODE_MDWREN),
+	       docptr + DOC_ASICMODECONFIRM);
+
+	write_nop(docptr);
+
+	return 0;
+}
+
+static int docg4_resume(struct platform_device *pdev)
+{
+
+	/*
+	 * Exit power-down.  Twelve consecutive reads of the address below
+	 * accomplishes this, assuming CE# has been asserted.
+	 */
+
+	struct docg4_priv *doc = platform_get_drvdata(pdev);
+	void __iomem *docptr = doc->virtadr;
+	int i;
+
+	dev_dbg(doc->dev, "%s...\n", __func__);
+
+	for (i = 0; i < 12; i++)
+		readb(docptr + 0x1fff);
+
+	return 0;
+}
+
+static void __init init_mtd_structs(struct mtd_info *mtd)
+{
+	/* initialize mtd and nand data structures */
+
+	/*
+	 * Note that some of the following initializations are not usually
+	 * required within a nand driver because they are performed by the nand
+	 * infrastructure code as part of nand_scan().  In this case they need
+	 * to be initialized here because we skip call to nand_scan_ident() (the
+	 * first half of nand_scan()).  The call to nand_scan_ident() is skipped
+	 * because for this device the chip id is not read in the manner of a
+	 * standard nand device.  Unfortunately, nand_scan_ident() does other
+	 * things as well, such as call nand_set_defaults().
+	 */
+
+	struct nand_chip *nand = mtd->priv;
+	struct docg4_priv *doc = nand->priv;
+
+	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->chipsize = DOCG4_CHIP_SIZE;
+	nand->chip_shift = DOCG4_CHIP_SHIFT;
+	nand->bbt_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->IO_ADDR_R = nand->IO_ADDR_W = doc->virtadr + DOC_IOSPACE_DATA;
+	nand->controller = &nand->hwcontrol;
+	spin_lock_init(&nand->controller->lock);
+	init_waitqueue_head(&nand->controller->wq);
+
+	/* 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;
+	}
+
+}
+
+static int __init read_id_reg(struct mtd_info *mtd)
+{
+	struct nand_chip *nand = mtd->priv;
+	struct docg4_priv *doc = nand->priv;
+	void __iomem *docptr = doc->virtadr;
+	uint16_t id1, id2;
+
+	/* check for presence of g4 chip by reading id registers */
+	id1 = readw(docptr + DOC_CHIPID);
+	id1 = readw(docptr + DOCG4_MYSTERY_REG);
+	id2 = readw(docptr + DOC_CHIPID_INV);
+	id2 = readw(docptr + DOCG4_MYSTERY_REG);
+
+	if (id1 == DOCG4_IDREG1_VALUE && id2 == DOCG4_IDREG2_VALUE) {
+		dev_info(doc->dev,
+			 "NAND device: 128MiB Diskonchip G4 detected\n");
+		return 0;
+	}
+
+	return -ENODEV;
+}
+
+static char const *part_probes[] = { "cmdlinepart", "saftlpart", NULL };
+
+static int __init probe_docg4(struct platform_device *pdev)
+{
+	struct mtd_info *mtd;
+	struct nand_chip *nand;
+	void __iomem *virtadr;
+	struct docg4_priv *doc;
+	int len, retval;
+	struct resource *r;
+	struct device *dev = &pdev->dev;
+
+	r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (r == NULL) {
+		dev_err(dev, "no io memory resource defined!\n");
+		return -ENODEV;
+	}
+
+	virtadr = ioremap(r->start, resource_size(r));
+	if (!virtadr) {
+		dev_err(dev, "Diskonchip ioremap failed: "
+			"0x%x bytes at 0x%x\n",
+			resource_size(r), r->start);
+		return -EIO;
+	}
+
+	len = sizeof(struct mtd_info) + sizeof(struct nand_chip) +
+		sizeof(struct docg4_priv);
+	mtd = kzalloc(len, GFP_KERNEL);
+	if (mtd == NULL) {
+		retval = -ENOMEM;
+		goto fail;
+	}
+	nand = (struct nand_chip *) (mtd + 1);
+	doc = (struct docg4_priv *) (nand + 1);
+	mtd->priv = nand;
+	nand->priv = doc;
+	mtd->owner = THIS_MODULE;
+	doc->virtadr = virtadr;
+	doc->dev = dev;
+
+	init_mtd_structs(mtd);
+
+	/* initialize kernel bch algorithm */
+	doc->bch = init_bch(DOCG4_M, DOCG4_T, DOCG4_PRIMITIVE_POLY);
+	if (doc->bch == NULL) {
+		retval = -EINVAL;
+		goto fail;
+	}
+
+	platform_set_drvdata(pdev, doc);
+
+	reset(mtd);
+	retval = read_id_reg(mtd);
+	if (retval == -ENODEV) {
+		dev_warn(dev, "No diskonchip G4 device found.\n");
+		goto fail;
+	}
+
+	retval = nand_scan_tail(mtd);
+	if (retval)
+		goto fail;
+
+	retval = read_factory_bbt(mtd);
+	if (retval)
+		goto fail;
+
+	retval = mtd_device_parse_register(mtd, part_probes, NULL, NULL, 0);
+	if (retval)
+		goto fail;
+
+	doc->mtd = mtd;
+	return 0;
+
+ fail:
+	iounmap(virtadr);
+	if (mtd) {
+		/* re-declarations avoid compiler warning */
+		struct nand_chip *nand = mtd->priv;
+		struct docg4_priv *doc = nand->priv;
+		nand_release(mtd); /* deletes partitions and mtd devices */
+		platform_set_drvdata(pdev, NULL);
+		free_bch(doc->bch);
+		kfree(mtd);
+	}
+
+	return retval;
+}
+
+static int __exit cleanup_docg4(struct platform_device *pdev)
+{
+	struct docg4_priv *doc = platform_get_drvdata(pdev);
+	nand_release(doc->mtd);
+	platform_set_drvdata(pdev, NULL);
+	free_bch(doc->bch);
+	kfree(doc->mtd);
+	iounmap(doc->virtadr);
+	return 0;
+}
+
+static struct platform_driver docg4_driver = {
+	.driver		= {
+		.name	= "docg4",
+		.owner	= THIS_MODULE,
+	},
+	.suspend	= docg4_suspend,
+	.resume		= docg4_resume,
+	.remove		= __exit_p(cleanup_docg4),
+};
+
+static int __init docg4_init(void)
+{
+	return platform_driver_probe(&docg4_driver, probe_docg4);
+}
+
+static void __exit docg4_exit(void)
+{
+	platform_driver_unregister(&docg4_driver);
+}
+
+module_init(docg4_init);
+module_exit(docg4_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Mike Dunn");
+MODULE_DESCRIPTION("M-Systems DiskOnChip G4 device driver");