/*
 *  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->ecc.strength = DOCG4_T;
        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: %pR\n", r);
                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");