// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Atmel AT45xxx DataFlash MTD driver for lightweight SPI framework
 *
 * Largely derived from at91_dataflash.c:
 *  Copyright (C) 2003-2005 SAN People (Pty) Ltd
*/
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/device.h>
#include <linux/mutex.h>
#include <linux/err.h>
#include <linux/math64.h>
#include <linux/of.h>
#include <linux/of_device.h>

#include <linux/spi/spi.h>
#include <linux/spi/flash.h>

#include <linux/mtd/mtd.h>
#include <linux/mtd/partitions.h>

/*
 * DataFlash is a kind of SPI flash.  Most AT45 chips have two buffers in
 * each chip, which may be used for double buffered I/O; but this driver
 * doesn't (yet) use these for any kind of i/o overlap or prefetching.
 *
 * Sometimes DataFlash is packaged in MMC-format cards, although the
 * MMC stack can't (yet?) distinguish between MMC and DataFlash
 * protocols during enumeration.
 */

/* reads can bypass the buffers */
#define OP_READ_CONTINUOUS      0xE8
#define OP_READ_PAGE            0xD2

/* group B requests can run even while status reports "busy" */
#define OP_READ_STATUS          0xD7    /* group B */

/* move data between host and buffer */
#define OP_READ_BUFFER1         0xD4    /* group B */
#define OP_READ_BUFFER2         0xD6    /* group B */
#define OP_WRITE_BUFFER1        0x84    /* group B */
#define OP_WRITE_BUFFER2        0x87    /* group B */

/* erasing flash */
#define OP_ERASE_PAGE           0x81
#define OP_ERASE_BLOCK          0x50

/* move data between buffer and flash */
#define OP_TRANSFER_BUF1        0x53
#define OP_TRANSFER_BUF2        0x55
#define OP_MREAD_BUFFER1        0xD4
#define OP_MREAD_BUFFER2        0xD6
#define OP_MWERASE_BUFFER1      0x83
#define OP_MWERASE_BUFFER2      0x86
#define OP_MWRITE_BUFFER1       0x88    /* sector must be pre-erased */
#define OP_MWRITE_BUFFER2       0x89    /* sector must be pre-erased */

/* write to buffer, then write-erase to flash */
#define OP_PROGRAM_VIA_BUF1     0x82
#define OP_PROGRAM_VIA_BUF2     0x85

/* compare buffer to flash */
#define OP_COMPARE_BUF1         0x60
#define OP_COMPARE_BUF2         0x61

/* read flash to buffer, then write-erase to flash */
#define OP_REWRITE_VIA_BUF1     0x58
#define OP_REWRITE_VIA_BUF2     0x59

/* newer chips report JEDEC manufacturer and device IDs; chip
 * serial number and OTP bits; and per-sector writeprotect.
 */
#define OP_READ_ID              0x9F
#define OP_READ_SECURITY        0x77
#define OP_WRITE_SECURITY_REVC  0x9A
#define OP_WRITE_SECURITY       0x9B    /* revision D */

#define CFI_MFR_ATMEL           0x1F

#define DATAFLASH_SHIFT_EXTID   24
#define DATAFLASH_SHIFT_ID      40

struct dataflash {
        u8                      command[4];
        char                    name[24];

        unsigned short          page_offset;    /* offset in flash address */
        unsigned int            page_size;      /* of bytes per page */

        struct mutex            lock;
        struct spi_device       *spi;

        struct mtd_info         mtd;
};

#ifdef CONFIG_OF
static const struct of_device_id dataflash_dt_ids[] = {
        { .compatible = "atmel,at45", },
        { .compatible = "atmel,dataflash", },
        { /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, dataflash_dt_ids);
#endif

/* ......................................................................... */

/*
 * Return the status of the DataFlash device.
 */
static inline int dataflash_status(struct spi_device *spi)
{
        /* NOTE:  at45db321c over 25 MHz wants to write
         * a dummy byte after the opcode...
         */
        return spi_w8r8(spi, OP_READ_STATUS);
}

/*
 * Poll the DataFlash device until it is READY.
 * This usually takes 5-20 msec or so; more for sector erase.
 */
static int dataflash_waitready(struct spi_device *spi)
{
        int     status;

        for (;;) {
                status = dataflash_status(spi);
                if (status < 0) {
                        dev_dbg(&spi->dev, "status %d?\n", status);
                        status = 0;
                }

                if (status & (1 << 7))  /* RDY/nBSY */
                        return status;

                usleep_range(3000, 4000);
        }
}

/* ......................................................................... */

/*
 * Erase pages of flash.
 */
static int dataflash_erase(struct mtd_info *mtd, struct erase_info *instr)
{
        struct dataflash        *priv = mtd->priv;
        struct spi_device       *spi = priv->spi;
        struct spi_transfer     x = { };
        struct spi_message      msg;
        unsigned                blocksize = priv->page_size << 3;
        u8                      *command;
        u32                     rem;

        dev_dbg(&spi->dev, "erase addr=0x%llx len 0x%llx\n",
                (long long)instr->addr, (long long)instr->len);

        div_u64_rem(instr->len, priv->page_size, &rem);
        if (rem)
                return -EINVAL;
        div_u64_rem(instr->addr, priv->page_size, &rem);
        if (rem)
                return -EINVAL;

        spi_message_init(&msg);

        x.tx_buf = command = priv->command;
        x.len = 4;
        spi_message_add_tail(&x, &msg);

        mutex_lock(&priv->lock);
        while (instr->len > 0) {
                unsigned int    pageaddr;
                int             status;
                int             do_block;

                /* Calculate flash page address; use block erase (for speed) if
                 * we're at a block boundary and need to erase the whole block.
                 */
                pageaddr = div_u64(instr->addr, priv->page_size);
                do_block = (pageaddr & 0x7) == 0 && instr->len >= blocksize;
                pageaddr = pageaddr << priv->page_offset;

                command[0] = do_block ? OP_ERASE_BLOCK : OP_ERASE_PAGE;
                command[1] = (u8)(pageaddr >> 16);
                command[2] = (u8)(pageaddr >> 8);
                command[3] = 0;

                dev_dbg(&spi->dev, "ERASE %s: (%x) %x %x %x [%i]\n",
                        do_block ? "block" : "page",
                        command[0], command[1], command[2], command[3],
                        pageaddr);

                status = spi_sync(spi, &msg);
                (void) dataflash_waitready(spi);

                if (status < 0) {
                        dev_err(&spi->dev, "erase %x, err %d\n",
                                pageaddr, status);
                        /* REVISIT:  can retry instr->retries times; or
                         * giveup and instr->fail_addr = instr->addr;
                         */
                        continue;
                }

                if (do_block) {
                        instr->addr += blocksize;
                        instr->len -= blocksize;
                } else {
                        instr->addr += priv->page_size;
                        instr->len -= priv->page_size;
                }
        }
        mutex_unlock(&priv->lock);

        return 0;
}

/*
 * Read from the DataFlash device.
 *   from   : Start offset in flash device
 *   len    : Amount to read
 *   retlen : About of data actually read
 *   buf    : Buffer containing the data
 */
static int dataflash_read(struct mtd_info *mtd, loff_t from, size_t len,
                               size_t *retlen, u_char *buf)
{
        struct dataflash        *priv = mtd->priv;
        struct spi_transfer     x[2] = { };
        struct spi_message      msg;
        unsigned int            addr;
        u8                      *command;
        int                     status;

        dev_dbg(&priv->spi->dev, "read 0x%x..0x%x\n",
                  (unsigned int)from, (unsigned int)(from + len));

        /* Calculate flash page/byte address */
        addr = (((unsigned)from / priv->page_size) << priv->page_offset)
                + ((unsigned)from % priv->page_size);

        command = priv->command;

        dev_dbg(&priv->spi->dev, "READ: (%x) %x %x %x\n",
                command[0], command[1], command[2], command[3]);

        spi_message_init(&msg);

        x[0].tx_buf = command;
        x[0].len = 8;
        spi_message_add_tail(&x[0], &msg);

        x[1].rx_buf = buf;
        x[1].len = len;
        spi_message_add_tail(&x[1], &msg);

        mutex_lock(&priv->lock);

        /* Continuous read, max clock = f(car) which may be less than
         * the peak rate available.  Some chips support commands with
         * fewer "don't care" bytes.  Both buffers stay unchanged.
         */
        command[0] = OP_READ_CONTINUOUS;
        command[1] = (u8)(addr >> 16);
        command[2] = (u8)(addr >> 8);
        command[3] = (u8)(addr >> 0);
        /* plus 4 "don't care" bytes */

        status = spi_sync(priv->spi, &msg);
        mutex_unlock(&priv->lock);

        if (status >= 0) {
                *retlen = msg.actual_length - 8;
                status = 0;
        } else
                dev_dbg(&priv->spi->dev, "read %x..%x --> %d\n",
                        (unsigned)from, (unsigned)(from + len),
                        status);
        return status;
}

/*
 * Write to the DataFlash device.
 *   to     : Start offset in flash device
 *   len    : Amount to write
 *   retlen : Amount of data actually written
 *   buf    : Buffer containing the data
 */
static int dataflash_write(struct mtd_info *mtd, loff_t to, size_t len,
                                size_t * retlen, const u_char * buf)
{
        struct dataflash        *priv = mtd->priv;
        struct spi_device       *spi = priv->spi;
        struct spi_transfer     x[2] = { };
        struct spi_message      msg;
        unsigned int            pageaddr, addr, offset, writelen;
        size_t                  remaining = len;
        u_char                  *writebuf = (u_char *) buf;
        int                     status = -EINVAL;
        u8                      *command;

        dev_dbg(&spi->dev, "write 0x%x..0x%x\n",
                (unsigned int)to, (unsigned int)(to + len));

        spi_message_init(&msg);

        x[0].tx_buf = command = priv->command;
        x[0].len = 4;
        spi_message_add_tail(&x[0], &msg);

        pageaddr = ((unsigned)to / priv->page_size);
        offset = ((unsigned)to % priv->page_size);
        if (offset + len > priv->page_size)
                writelen = priv->page_size - offset;
        else
                writelen = len;

        mutex_lock(&priv->lock);
        while (remaining > 0) {
                dev_dbg(&spi->dev, "write @ %i:%i len=%i\n",
                        pageaddr, offset, writelen);

                /* REVISIT:
                 * (a) each page in a sector must be rewritten at least
                 *     once every 10K sibling erase/program operations.
                 * (b) for pages that are already erased, we could
                 *     use WRITE+MWRITE not PROGRAM for ~30% speedup.
                 * (c) WRITE to buffer could be done while waiting for
                 *     a previous MWRITE/MWERASE to complete ...
                 * (d) error handling here seems to be mostly missing.
                 *
                 * Two persistent bits per page, plus a per-sector counter,
                 * could support (a) and (b) ... we might consider using
                 * the second half of sector zero, which is just one block,
                 * to track that state.  (On AT91, that sector should also
                 * support boot-from-DataFlash.)
                 */

                addr = pageaddr << priv->page_offset;

                /* (1) Maybe transfer partial page to Buffer1 */
                if (writelen != priv->page_size) {
                        command[0] = OP_TRANSFER_BUF1;
                        command[1] = (addr & 0x00FF0000) >> 16;
                        command[2] = (addr & 0x0000FF00) >> 8;
                        command[3] = 0;

                        dev_dbg(&spi->dev, "TRANSFER: (%x) %x %x %x\n",
                                command[0], command[1], command[2], command[3]);

                        status = spi_sync(spi, &msg);
                        if (status < 0)
                                dev_dbg(&spi->dev, "xfer %u -> %d\n",
                                        addr, status);

                        (void) dataflash_waitready(priv->spi);
                }

                /* (2) Program full page via Buffer1 */
                addr += offset;
                command[0] = OP_PROGRAM_VIA_BUF1;
                command[1] = (addr & 0x00FF0000) >> 16;
                command[2] = (addr & 0x0000FF00) >> 8;
                command[3] = (addr & 0x000000FF);

                dev_dbg(&spi->dev, "PROGRAM: (%x) %x %x %x\n",
                        command[0], command[1], command[2], command[3]);

                x[1].tx_buf = writebuf;
                x[1].len = writelen;
                spi_message_add_tail(x + 1, &msg);
                status = spi_sync(spi, &msg);
                spi_transfer_del(x + 1);
                if (status < 0)
                        dev_dbg(&spi->dev, "pgm %u/%u -> %d\n",
                                addr, writelen, status);

                (void) dataflash_waitready(priv->spi);


#ifdef CONFIG_MTD_DATAFLASH_WRITE_VERIFY

                /* (3) Compare to Buffer1 */
                addr = pageaddr << priv->page_offset;
                command[0] = OP_COMPARE_BUF1;
                command[1] = (addr & 0x00FF0000) >> 16;
                command[2] = (addr & 0x0000FF00) >> 8;
                command[3] = 0;

                dev_dbg(&spi->dev, "COMPARE: (%x) %x %x %x\n",
                        command[0], command[1], command[2], command[3]);

                status = spi_sync(spi, &msg);
                if (status < 0)
                        dev_dbg(&spi->dev, "compare %u -> %d\n",
                                addr, status);

                status = dataflash_waitready(priv->spi);

                /* Check result of the compare operation */
                if (status & (1 << 6)) {
                        dev_err(&spi->dev, "compare page %u, err %d\n",
                                pageaddr, status);
                        remaining = 0;
                        status = -EIO;
                        break;
                } else
                        status = 0;

#endif  /* CONFIG_MTD_DATAFLASH_WRITE_VERIFY */

                remaining = remaining - writelen;
                pageaddr++;
                offset = 0;
                writebuf += writelen;
                *retlen += writelen;

                if (remaining > priv->page_size)
                        writelen = priv->page_size;
                else
                        writelen = remaining;
        }
        mutex_unlock(&priv->lock);

        return status;
}

/* ......................................................................... */

#ifdef CONFIG_MTD_DATAFLASH_OTP

static int dataflash_get_otp_info(struct mtd_info *mtd, size_t len,
                                  size_t *retlen, struct otp_info *info)
{
        /* Report both blocks as identical:  bytes 0..64, locked.
         * Unless the user block changed from all-ones, we can't
         * tell whether it's still writable; so we assume it isn't.
         */
        info->start = 0;
        info->length = 64;
        info->locked = 1;
        *retlen = sizeof(*info);
        return 0;
}

static ssize_t otp_read(struct spi_device *spi, unsigned base,
                u8 *buf, loff_t off, size_t len)
{
        struct spi_message      m;
        size_t                  l;
        u8                      *scratch;
        struct spi_transfer     t;
        int                     status;

        if (off > 64)
                return -EINVAL;

        if ((off + len) > 64)
                len = 64 - off;

        spi_message_init(&m);

        l = 4 + base + off + len;
        scratch = kzalloc(l, GFP_KERNEL);
        if (!scratch)
                return -ENOMEM;

        /* OUT: OP_READ_SECURITY, 3 don't-care bytes, zeroes
         * IN:  ignore 4 bytes, data bytes 0..N (max 127)
         */
        scratch[0] = OP_READ_SECURITY;

        memset(&t, 0, sizeof t);
        t.tx_buf = scratch;
        t.rx_buf = scratch;
        t.len = l;
        spi_message_add_tail(&t, &m);

        dataflash_waitready(spi);

        status = spi_sync(spi, &m);
        if (status >= 0) {
                memcpy(buf, scratch + 4 + base + off, len);
                status = len;
        }

        kfree(scratch);
        return status;
}

static int dataflash_read_fact_otp(struct mtd_info *mtd,
                loff_t from, size_t len, size_t *retlen, u_char *buf)
{
        struct dataflash        *priv = mtd->priv;
        int                     status;

        /* 64 bytes, from 0..63 ... start at 64 on-chip */
        mutex_lock(&priv->lock);
        status = otp_read(priv->spi, 64, buf, from, len);
        mutex_unlock(&priv->lock);

        if (status < 0)
                return status;
        *retlen = status;
        return 0;
}

static int dataflash_read_user_otp(struct mtd_info *mtd,
                loff_t from, size_t len, size_t *retlen, u_char *buf)
{
        struct dataflash        *priv = mtd->priv;
        int                     status;

        /* 64 bytes, from 0..63 ... start at 0 on-chip */
        mutex_lock(&priv->lock);
        status = otp_read(priv->spi, 0, buf, from, len);
        mutex_unlock(&priv->lock);

        if (status < 0)
                return status;
        *retlen = status;
        return 0;
}

static int dataflash_write_user_otp(struct mtd_info *mtd,
                loff_t from, size_t len, size_t *retlen, const u_char *buf)
{
        struct spi_message      m;
        const size_t            l = 4 + 64;
        u8                      *scratch;
        struct spi_transfer     t;
        struct dataflash        *priv = mtd->priv;
        int                     status;

        if (from >= 64) {
                /*
                 * Attempting to write beyond the end of OTP memory,
                 * no data can be written.
                 */
                *retlen = 0;
                return 0;
        }

        /* Truncate the write to fit into OTP memory. */
        if ((from + len) > 64)
                len = 64 - from;

        /* OUT: OP_WRITE_SECURITY, 3 zeroes, 64 data-or-zero bytes
         * IN:  ignore all
         */
        scratch = kzalloc(l, GFP_KERNEL);
        if (!scratch)
                return -ENOMEM;
        scratch[0] = OP_WRITE_SECURITY;
        memcpy(scratch + 4 + from, buf, len);

        spi_message_init(&m);

        memset(&t, 0, sizeof t);
        t.tx_buf = scratch;
        t.len = l;
        spi_message_add_tail(&t, &m);

        /* Write the OTP bits, if they've not yet been written.
         * This modifies SRAM buffer1.
         */
        mutex_lock(&priv->lock);
        dataflash_waitready(priv->spi);
        status = spi_sync(priv->spi, &m);
        mutex_unlock(&priv->lock);

        kfree(scratch);

        if (status >= 0) {
                status = 0;
                *retlen = len;
        }
        return status;
}

static char *otp_setup(struct mtd_info *device, char revision)
{
        device->_get_fact_prot_info = dataflash_get_otp_info;
        device->_read_fact_prot_reg = dataflash_read_fact_otp;
        device->_get_user_prot_info = dataflash_get_otp_info;
        device->_read_user_prot_reg = dataflash_read_user_otp;

        /* rev c parts (at45db321c and at45db1281 only!) use a
         * different write procedure; not (yet?) implemented.
         */
        if (revision > 'c')
                device->_write_user_prot_reg = dataflash_write_user_otp;

        return ", OTP";
}

#else

static char *otp_setup(struct mtd_info *device, char revision)
{
        return " (OTP)";
}

#endif

/* ......................................................................... */

/*
 * Register DataFlash device with MTD subsystem.
 */
static int add_dataflash_otp(struct spi_device *spi, char *name, int nr_pages,
                             int pagesize, int pageoffset, char revision)
{
        struct dataflash                *priv;
        struct mtd_info                 *device;
        struct flash_platform_data      *pdata = dev_get_platdata(&spi->dev);
        char                            *otp_tag = "";
        int                             err = 0;

        priv = kzalloc(sizeof *priv, GFP_KERNEL);
        if (!priv)
                return -ENOMEM;

        mutex_init(&priv->lock);
        priv->spi = spi;
        priv->page_size = pagesize;
        priv->page_offset = pageoffset;

        /* name must be usable with cmdlinepart */
        sprintf(priv->name, "spi%d.%d-%s",
                        spi->master->bus_num, spi->chip_select,
                        name);

        device = &priv->mtd;
        device->name = (pdata && pdata->name) ? pdata->name : priv->name;
        device->size = nr_pages * pagesize;
        device->erasesize = pagesize;
        device->writesize = pagesize;
        device->type = MTD_DATAFLASH;
        device->flags = MTD_WRITEABLE;
        device->_erase = dataflash_erase;
        device->_read = dataflash_read;
        device->_write = dataflash_write;
        device->priv = priv;

        device->dev.parent = &spi->dev;
        mtd_set_of_node(device, spi->dev.of_node);

        if (revision >= 'c')
                otp_tag = otp_setup(device, revision);

        dev_info(&spi->dev, "%s (%lld KBytes) pagesize %d bytes%s\n",
                        name, (long long)((device->size + 1023) >> 10),
                        pagesize, otp_tag);
        spi_set_drvdata(spi, priv);

        err = mtd_device_register(device,
                        pdata ? pdata->parts : NULL,
                        pdata ? pdata->nr_parts : 0);

        if (!err)
                return 0;

        kfree(priv);
        return err;
}

static inline int add_dataflash(struct spi_device *spi, char *name,
                                int nr_pages, int pagesize, int pageoffset)
{
        return add_dataflash_otp(spi, name, nr_pages, pagesize,
                        pageoffset, 0);
}

struct flash_info {
        char            *name;

        /* JEDEC id has a high byte of zero plus three data bytes:
         * the manufacturer id, then a two byte device id.
         */
        u64             jedec_id;

        /* The size listed here is what works with OP_ERASE_PAGE. */
        unsigned        nr_pages;
        u16             pagesize;
        u16             pageoffset;

        u16             flags;
#define SUP_EXTID       0x0004          /* supports extended ID data */
#define SUP_POW2PS      0x0002          /* supports 2^N byte pages */
#define IS_POW2PS       0x0001          /* uses 2^N byte pages */
};

static struct flash_info dataflash_data[] = {

        /*
         * NOTE:  chips with SUP_POW2PS (rev D and up) need two entries,
         * one with IS_POW2PS and the other without.  The entry with the
         * non-2^N byte page size can't name exact chip revisions without
         * losing backwards compatibility for cmdlinepart.
         *
         * These newer chips also support 128-byte security registers (with
         * 64 bytes one-time-programmable) and software write-protection.
         */
        { "AT45DB011B",  0x1f2200, 512, 264, 9, SUP_POW2PS},
        { "at45db011d",  0x1f2200, 512, 256, 8, SUP_POW2PS | IS_POW2PS},

        { "AT45DB021B",  0x1f2300, 1024, 264, 9, SUP_POW2PS},
        { "at45db021d",  0x1f2300, 1024, 256, 8, SUP_POW2PS | IS_POW2PS},

        { "AT45DB041x",  0x1f2400, 2048, 264, 9, SUP_POW2PS},
        { "at45db041d",  0x1f2400, 2048, 256, 8, SUP_POW2PS | IS_POW2PS},

        { "AT45DB081B",  0x1f2500, 4096, 264, 9, SUP_POW2PS},
        { "at45db081d",  0x1f2500, 4096, 256, 8, SUP_POW2PS | IS_POW2PS},

        { "AT45DB161x",  0x1f2600, 4096, 528, 10, SUP_POW2PS},
        { "at45db161d",  0x1f2600, 4096, 512, 9, SUP_POW2PS | IS_POW2PS},

        { "AT45DB321x",  0x1f2700, 8192, 528, 10, 0},           /* rev C */

        { "AT45DB321x",  0x1f2701, 8192, 528, 10, SUP_POW2PS},
        { "at45db321d",  0x1f2701, 8192, 512, 9, SUP_POW2PS | IS_POW2PS},

        { "AT45DB642x",  0x1f2800, 8192, 1056, 11, SUP_POW2PS},
        { "at45db642d",  0x1f2800, 8192, 1024, 10, SUP_POW2PS | IS_POW2PS},

        { "AT45DB641E",  0x1f28000100ULL, 32768, 264, 9, SUP_EXTID | SUP_POW2PS},
        { "at45db641e",  0x1f28000100ULL, 32768, 256, 8, SUP_EXTID | SUP_POW2PS | IS_POW2PS},
};

static struct flash_info *jedec_lookup(struct spi_device *spi,
                                       u64 jedec, bool use_extid)
{
        struct flash_info *info;
        int status;

        for (info = dataflash_data;
             info < dataflash_data + ARRAY_SIZE(dataflash_data);
             info++) {
                if (use_extid && !(info->flags & SUP_EXTID))
                        continue;

                if (info->jedec_id == jedec) {
                        dev_dbg(&spi->dev, "OTP, sector protect%s\n",
                                (info->flags & SUP_POW2PS) ?
                                ", binary pagesize" : "");
                        if (info->flags & SUP_POW2PS) {
                                status = dataflash_status(spi);
                                if (status < 0) {
                                        dev_dbg(&spi->dev, "status error %d\n",
                                                status);
                                        return ERR_PTR(status);
                                }
                                if (status & 0x1) {
                                        if (info->flags & IS_POW2PS)
                                                return info;
                                } else {
                                        if (!(info->flags & IS_POW2PS))
                                                return info;
                                }
                        } else
                                return info;
                }
        }

        return ERR_PTR(-ENODEV);
}

static struct flash_info *jedec_probe(struct spi_device *spi)
{
        int ret;
        u8 code = OP_READ_ID;
        u64 jedec;
        u8 id[sizeof(jedec)] = {0};
        const unsigned int id_size = 5;
        struct flash_info *info;

        /*
         * JEDEC also defines an optional "extended device information"
         * string for after vendor-specific data, after the three bytes
         * we use here.  Supporting some chips might require using it.
         *
         * If the vendor ID isn't Atmel's (0x1f), assume this call failed.
         * That's not an error; only rev C and newer chips handle it, and
         * only Atmel sells these chips.
         */
        ret = spi_write_then_read(spi, &code, 1, id, id_size);
        if (ret < 0) {
                dev_dbg(&spi->dev, "error %d reading JEDEC ID\n", ret);
                return ERR_PTR(ret);
        }

        if (id[0] != CFI_MFR_ATMEL)
                return NULL;

        jedec = be64_to_cpup((__be64 *)id);

        /*
         * First, try to match device using extended device
         * information
         */
        info = jedec_lookup(spi, jedec >> DATAFLASH_SHIFT_EXTID, true);
        if (!IS_ERR(info))
                return info;
        /*
         * If that fails, make another pass using regular ID
         * information
         */
        info = jedec_lookup(spi, jedec >> DATAFLASH_SHIFT_ID, false);
        if (!IS_ERR(info))
                return info;
        /*
         * Treat other chips as errors ... we won't know the right page
         * size (it might be binary) even when we can tell which density
         * class is involved (legacy chip id scheme).
         */
        dev_warn(&spi->dev, "JEDEC id %016llx not handled\n", jedec);
        return ERR_PTR(-ENODEV);
}

/*
 * Detect and initialize DataFlash device, using JEDEC IDs on newer chips
 * or else the ID code embedded in the status bits:
 *
 *   Device      Density         ID code          #Pages PageSize  Offset
 *   AT45DB011B  1Mbit   (128K)  xx0011xx (0x0c)    512    264      9
 *   AT45DB021B  2Mbit   (256K)  xx0101xx (0x14)   1024    264      9
 *   AT45DB041B  4Mbit   (512K)  xx0111xx (0x1c)   2048    264      9
 *   AT45DB081B  8Mbit   (1M)    xx1001xx (0x24)   4096    264      9
 *   AT45DB0161B 16Mbit  (2M)    xx1011xx (0x2c)   4096    528     10
 *   AT45DB0321B 32Mbit  (4M)    xx1101xx (0x34)   8192    528     10
 *   AT45DB0642  64Mbit  (8M)    xx111xxx (0x3c)   8192   1056     11
 *   AT45DB1282  128Mbit (16M)   xx0100xx (0x10)  16384   1056     11
 */
static int dataflash_probe(struct spi_device *spi)
{
        int status;
        struct flash_info       *info;

        /*
         * Try to detect dataflash by JEDEC ID.
         * If it succeeds we know we have either a C or D part.
         * D will support power of 2 pagesize option.
         * Both support the security register, though with different
         * write procedures.
         */
        info = jedec_probe(spi);
        if (IS_ERR(info))
                return PTR_ERR(info);
        if (info != NULL)
                return add_dataflash_otp(spi, info->name, info->nr_pages,
                                info->pagesize, info->pageoffset,
                                (info->flags & SUP_POW2PS) ? 'd' : 'c');

        /*
         * Older chips support only legacy commands, identifing
         * capacity using bits in the status byte.
         */
        status = dataflash_status(spi);
        if (status <= 0 || status == 0xff) {
                dev_dbg(&spi->dev, "status error %d\n", status);
                if (status == 0 || status == 0xff)
                        status = -ENODEV;
                return status;
        }

        /* if there's a device there, assume it's dataflash.
         * board setup should have set spi->max_speed_max to
         * match f(car) for continuous reads, mode 0 or 3.
         */
        switch (status & 0x3c) {
        case 0x0c:      /* 0 0 1 1 x x */
                status = add_dataflash(spi, "AT45DB011B", 512, 264, 9);
                break;
        case 0x14:      /* 0 1 0 1 x x */
                status = add_dataflash(spi, "AT45DB021B", 1024, 264, 9);
                break;
        case 0x1c:      /* 0 1 1 1 x x */
                status = add_dataflash(spi, "AT45DB041x", 2048, 264, 9);
                break;
        case 0x24:      /* 1 0 0 1 x x */
                status = add_dataflash(spi, "AT45DB081B", 4096, 264, 9);
                break;
        case 0x2c:      /* 1 0 1 1 x x */
                status = add_dataflash(spi, "AT45DB161x", 4096, 528, 10);
                break;
        case 0x34:      /* 1 1 0 1 x x */
                status = add_dataflash(spi, "AT45DB321x", 8192, 528, 10);
                break;
        case 0x38:      /* 1 1 1 x x x */
        case 0x3c:
                status = add_dataflash(spi, "AT45DB642x", 8192, 1056, 11);
                break;
        /* obsolete AT45DB1282 not (yet?) supported */
        default:
                dev_info(&spi->dev, "unsupported device (%x)\n",
                                status & 0x3c);
                status = -ENODEV;
        }

        if (status < 0)
                dev_dbg(&spi->dev, "add_dataflash --> %d\n", status);

        return status;
}

static int dataflash_remove(struct spi_device *spi)
{
        struct dataflash        *flash = spi_get_drvdata(spi);
        int                     status;

        dev_dbg(&spi->dev, "remove\n");

        status = mtd_device_unregister(&flash->mtd);
        if (status == 0)
                kfree(flash);
        return status;
}

static struct spi_driver dataflash_driver = {
        .driver = {
                .name           = "mtd_dataflash",
                .of_match_table = of_match_ptr(dataflash_dt_ids),
        },

        .probe          = dataflash_probe,
        .remove         = dataflash_remove,

        /* FIXME:  investigate suspend and resume... */
};

module_spi_driver(dataflash_driver);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Andrew Victor, David Brownell");
MODULE_DESCRIPTION("MTD DataFlash driver");
MODULE_ALIAS("spi:mtd_dataflash");