nuttx/drivers/mtd/w25.c

/****************************************************************************
 * drivers/mtd/w25.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/* Driver for SPI-based W25x16, x32, and x64 and W25q16, q32, q64, and q128
 * FLASH from Winbond (and work-alike parts from AMIC)
 */

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <sys/types.h>

#include <inttypes.h>
#include <stdbool.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>

#include <nuttx/kmalloc.h>
#include <nuttx/signal.h>
#include <nuttx/fs/ioctl.h>
#include <nuttx/spi/spi.h>
#include <nuttx/mtd/mtd.h>

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

/* You can enable just the W25 traces; else its convoluted potentially with
 * high number of other traces from fs.
 */

#ifdef CONFIG_W25_DEBUG
#  define w25_finfo  _info
#  define w25_ferr   _err
#else
#  define w25_finfo  finfo
#  define w25_ferr   ferr
#endif

/* Configuration ************************************************************/

/* Per the data sheet, the W25 parts can be driven with either SPI mode 0
 * (CPOL=0 and CPHA=0) or mode 3 (CPOL=1 and CPHA=1).
 * But I have heard that other devices can operate in mode 0 or 1.
 * So you may need to specify CONFIG_W25_SPIMODE to select the best mode
 * for your device.  If CONFIG_W25_SPIMODE is not defined, mode 0 will be
 * used.
 */

#ifndef CONFIG_W25_SPIMODE
#  define CONFIG_W25_SPIMODE SPIDEV_MODE0
#endif

/* SPI Frequency.  May be up to 25MHz. */

#ifndef CONFIG_W25_SPIFREQUENCY
#  define CONFIG_W25_SPIFREQUENCY 20000000
#endif

/* W25 Instructions *********************************************************/

#define W25_WREN                   0x06    /* Write enable                   */
#define W25_WRDI                   0x04    /* Write Disable                  */
#define W25_RDSR                   0x05    /* Read status register           */
#define W25_WRSR                   0x01    /* Write Status Register          */
#define W25_RDDATA                 0x03    /* Read data bytes                */
#define W25_FRD                    0x0b    /* Higher speed read              */
#define W25_FRDD                   0x3b    /* Fast read, dual output         */
#define W25_PP                     0x02    /* Program page                   */
#define W25_BE                     0xd8    /* Block Erase (64KB)             */
#define W25_SE                     0x20    /* Sector erase (4KB)             */
#define W25_CE                     0xc7    /* Chip erase                     */
#define W25_PD                     0xb9    /* Power down                     */
#define W25_PURDID                 0xab    /* Release PD, Device ID          */
#define W25_RDMFID                 0x90    /* Read Manufacturer / Device     */
#define W25_JEDEC_ID               0x9f    /* JEDEC ID read                  */

/* W25 Registers ************************************************************/

/* Read ID (RDID) register values */

#define W25_MANUFACTURER           0xef   /* Winbond Serial Flash */
#define W25X16_DEVID               0x14   /* W25X16 device ID (0xab, 0x90) */
#define W25X32_DEVID               0x15   /* W25X16 device ID (0xab, 0x90) */
#define W25X64_DEVID               0x16   /* W25X16 device ID (0xab, 0x90) */

/* JEDEC Read ID register values */

#define W25_JEDEC_WINBOND          0xef  /* Winbond manufacturer ID */
#define W25_JEDEC_AMIC             0x37  /* AMIC manufacturer ID */

#define W25X_JEDEC_MEMORY_TYPE     0x30  /* W25X memory type */
#define W25Q_JEDEC_MEMORY_TYPE_A   0x40  /* W25Q memory type */
#define W25Q_JEDEC_MEMORY_TYPE_B   0x60  /* W25Q memory type */
#define W25Q_JEDEC_MEMORY_TYPE_C   0x50  /* W25Q memory type */
#define W25Q_JEDEC_MEMORY_TYPE_D   0x70  /* W25QJV memory type (backward compatible) */

#define W25_JEDEC_CAPACITY_2MBIT   0x12  /* 256x1024  = 2Mbit memory capacity */
#define W25_JEDEC_CAPACITY_8MBIT   0x14  /* 256x4096  = 8Mbit memory capacity */
#define W25_JEDEC_CAPACITY_16MBIT  0x15  /* 512x4096  = 16Mbit memory capacity */
#define W25_JEDEC_CAPACITY_32MBIT  0x16  /* 1024x4096 = 32Mbit memory capacity */
#define W25_JEDEC_CAPACITY_64MBIT  0x17  /* 2048x4096 = 64Mbit memory capacity */
#define W25_JEDEC_CAPACITY_128MBIT 0x18  /* 4096x4096 = 128Mbit memory capacity */

#define NSECTORS_2MBIT             64    /* 64 sectors x 4096 bytes/sector = 256Kb */
#define NSECTORS_8MBIT             256   /* 256 sectors x 4096 bytes/sector = 1Mb */
#define NSECTORS_16MBIT            512   /* 512 sectors x 4096 bytes/sector = 2Mb */
#define NSECTORS_32MBIT            1024  /* 1024 sectors x 4096 bytes/sector = 4Mb */
#define NSECTORS_64MBIT            2048  /* 2048 sectors x 4096 bytes/sector = 8Mb */
#define NSECTORS_128MBIT           4096  /* 4096 sectors x 4096 bytes/sector = 16Mb */

/* Status register bit definitions */

#define W25_SR_BUSY                (1 << 0)  /* Bit 0: Write in progress */
#define W25_SR_WEL                 (1 << 1)  /* Bit 1: Write enable latch bit */
#define W25_SR_BP_SHIFT            (2)       /* Bits 2-5: Block protect bits */
#define W25_SR_BP_MASK             (15 << W25_SR_BP_SHIFT)
#  define W25X16_SR_BP_NONE        (0 << W25_SR_BP_SHIFT)  /* Unprotected */
#  define W25X16_SR_BP_UPPER32nd   (1 << W25_SR_BP_SHIFT)  /* Upper 32nd */
#  define W25X16_SR_BP_UPPER16th   (2 << W25_SR_BP_SHIFT)  /* Upper 16th */
#  define W25X16_SR_BP_UPPER8th    (3 << W25_SR_BP_SHIFT)  /* Upper 8th */
#  define W25X16_SR_BP_UPPERQTR    (4 << W25_SR_BP_SHIFT)  /* Upper quarter */
#  define W25X16_SR_BP_UPPERHALF   (5 << W25_SR_BP_SHIFT)  /* Upper half */
#  define W25X16_SR_BP_ALL         (6 << W25_SR_BP_SHIFT)  /* All sectors */
#  define W25X16_SR_BP_LOWER32nd   (9 << W25_SR_BP_SHIFT)  /* Lower 32nd */
#  define W25X16_SR_BP_LOWER16th   (10 << W25_SR_BP_SHIFT) /* Lower 16th */
#  define W25X16_SR_BP_LOWER8th    (11 << W25_SR_BP_SHIFT) /* Lower 8th */
#  define W25X16_SR_BP_LOWERQTR    (12 << W25_SR_BP_SHIFT) /* Lower quarter */
#  define W25X16_SR_BP_LOWERHALF   (13 << W25_SR_BP_SHIFT) /* Lower half */

#  define W25X32_SR_BP_NONE        (0 << W25_SR_BP_SHIFT)  /* Unprotected */
#  define W25X32_SR_BP_UPPER64th   (1 << W25_SR_BP_SHIFT)  /* Upper 64th */
#  define W25X32_SR_BP_UPPER32nd   (2 << W25_SR_BP_SHIFT)  /* Upper 32nd */
#  define W25X32_SR_BP_UPPER16th   (3 << W25_SR_BP_SHIFT)  /* Upper 16th */
#  define W25X32_SR_BP_UPPER8th    (4 << W25_SR_BP_SHIFT)  /* Upper 8th */
#  define W25X32_SR_BP_UPPERQTR    (5 << W25_SR_BP_SHIFT)  /* Upper quarter */
#  define W25X32_SR_BP_UPPERHALF   (6 << W25_SR_BP_SHIFT)  /* Upper half */
#  define W25X32_SR_BP_ALL         (7 << W25_SR_BP_SHIFT)  /* All sectors */
#  define W25X32_SR_BP_LOWER64th   (9 << W25_SR_BP_SHIFT)  /* Lower 64th */
#  define W25X32_SR_BP_LOWER32nd   (10 << W25_SR_BP_SHIFT) /* Lower 32nd */
#  define W25X32_SR_BP_LOWER16th   (11 << W25_SR_BP_SHIFT) /* Lower 16th */
#  define W25X32_SR_BP_LOWER8th    (12 << W25_SR_BP_SHIFT) /* Lower 8th */
#  define W25X32_SR_BP_LOWERQTR    (13 << W25_SR_BP_SHIFT) /* Lower quarter */
#  define W25X32_SR_BP_LOWERHALF   (14 << W25_SR_BP_SHIFT) /* Lower half */

#  define W25X64_SR_BP_NONE        (0 << W25_SR_BP_SHIFT)  /* Unprotected */
#  define W25X64_SR_BP_UPPER64th   (1 << W25_SR_BP_SHIFT)  /* Upper 64th */
#  define W25X64_SR_BP_UPPER32nd   (2 << W25_SR_BP_SHIFT)  /* Upper 32nd */
#  define W25X64_SR_BP_UPPER16th   (3 << W25_SR_BP_SHIFT)  /* Upper 16th */
#  define W25X64_SR_BP_UPPER8th    (4 << W25_SR_BP_SHIFT)  /* Upper 8th */
#  define W25X64_SR_BP_UPPERQTR    (5 << W25_SR_BP_SHIFT)  /* Upper quarter */
#  define W25X64_SR_BP_UPPERHALF   (6 << W25_SR_BP_SHIFT)  /* Upper half */
#  define W25X46_SR_BP_ALL         (7 << W25_SR_BP_SHIFT)  /* All sectors */
#  define W25X64_SR_BP_LOWER64th   (9 << W25_SR_BP_SHIFT)  /* Lower 64th */
#  define W25X64_SR_BP_LOWER32nd   (10 << W25_SR_BP_SHIFT) /* Lower 32nd */
#  define W25X64_SR_BP_LOWER16th   (11 << W25_SR_BP_SHIFT) /* Lower 16th */
#  define W25X64_SR_BP_LOWER8th    (12 << W25_SR_BP_SHIFT) /* Lower 8th */
#  define W25X64_SR_BP_LOWERQTR    (13 << W25_SR_BP_SHIFT) /* Lower quarter */
#  define W25X64_SR_BP_LOWERHALF   (14 << W25_SR_BP_SHIFT) /* Lower half */

                                             /* Bit 6: Reserved */
#define W25_SR_SRP                 (1 << 7)  /* Bit 7: Status register write protect */

#define W25_DUMMY                  0xa5

/* Chip Geometries **********************************************************/

/* All members of the family support uniform 4K-byte sectors and 256 byte
 * pages
 */

#define W25_SECTOR_SHIFT           12        /* Sector size 1 << 12 = 4Kb */
#define W25_SECTOR_SIZE            (1 << 12) /* Sector size 1 << 12 = 4Kb */
#define W25_PAGE_SHIFT             8         /* Sector size 1 << 8 = 256b */
#define W25_PAGE_SIZE              (1 << 8)  /* Sector size 1 << 8 = 256b */

#ifdef CONFIG_W25_SECTOR512                  /* Simulate a 512 byte sector */
#  define W25_SECTOR512_SHIFT      9         /* Sector size 1 << 9 = 512 bytes */
#  define W25_SECTOR512_SIZE       (1 << 9)  /* Sector size 1 << 9 = 512 bytes */
#endif

#define W25_ERASED_STATE           0xff      /* State of FLASH when erased */

/* Cache flags */

#define W25_CACHE_VALID            (1 << 0)  /* 1=Cache has valid data */
#define W25_CACHE_DIRTY            (1 << 1)  /* 1=Cache is dirty */
#define W25_CACHE_ERASED           (1 << 2)  /* 1=Backing FLASH is erased */

#define IS_VALID(p)                ((((p)->flags) & W25_CACHE_VALID) != 0)
#define IS_DIRTY(p)                ((((p)->flags) & W25_CACHE_DIRTY) != 0)
#define IS_ERASED(p)               ((((p)->flags) & W25_CACHE_ERASED) != 0)

#define SET_VALID(p)               do { (p)->flags |= W25_CACHE_VALID; } while (0)
#define SET_DIRTY(p)               do { (p)->flags |= W25_CACHE_DIRTY; } while (0)
#define SET_ERASED(p)              do { (p)->flags |= W25_CACHE_ERASED; } while (0)

#define CLR_VALID(p)               do { (p)->flags &= ~W25_CACHE_VALID; } while (0)
#define CLR_DIRTY(p)               do { (p)->flags &= ~W25_CACHE_DIRTY; } while (0)
#define CLR_ERASED(p)              do { (p)->flags &= ~W25_CACHE_ERASED; } while (0)

/****************************************************************************
 * Private Types
 ****************************************************************************/

/* This type represents the state of the MTD device.
 * The struct mtd_dev_s must appear at the beginning of the definition so
 * that you can freely cast between pointers to struct mtd_dev_s and struct
 * w25_dev_s.
 */

struct w25_dev_s
{
  struct mtd_dev_s      mtd;         /* MTD interface */
  FAR struct spi_dev_s *spi;         /* Saved SPI interface instance */
  uint16_t              nsectors;    /* Number of erase sectors */
  uint8_t               prev_instr;  /* Previous instruction given to W25 device */

#if defined(CONFIG_W25_SECTOR512) && !defined(CONFIG_W25_READONLY)
  uint8_t               flags;       /* Buffered sector flags */
  uint16_t              esectno;     /* Erase sector number in the cache */
  FAR uint8_t          *sector;      /* Allocated sector data */
#endif
};

/****************************************************************************
 * Private Function Prototypes
 ****************************************************************************/

/* Helpers */

static void w25_lock(FAR struct spi_dev_s *spi);
static inline void w25_unlock(FAR struct spi_dev_s *spi);
static inline int w25_readid(FAR struct w25_dev_s *priv);
#ifndef CONFIG_W25_READONLY
static void w25_unprotect(FAR struct w25_dev_s *priv);
#endif
static uint8_t w25_waitwritecomplete(FAR struct w25_dev_s *priv);
static inline void w25_wren(FAR struct w25_dev_s *priv);
static inline void w25_wrdi(FAR struct w25_dev_s *priv);
static bool w25_is_erased(struct w25_dev_s *priv,
                          off_t address,
                          off_t size);
static void w25_sectorerase(FAR struct w25_dev_s *priv,
                            off_t offset);
static inline int w25_chiperase(FAR struct w25_dev_s *priv);
static void w25_byteread(FAR struct w25_dev_s *priv,
                         FAR uint8_t *buffer,
                         off_t address,
                         size_t nbytes);
#ifndef CONFIG_W25_READONLY
static void w25_pagewrite(FAR struct w25_dev_s *priv,
                          FAR const uint8_t *buffer,
                          off_t address,
                          size_t nbytes);
#endif
#ifdef CONFIG_W25_SECTOR512
static void w25_cacheflush(struct w25_dev_s *priv);
static FAR uint8_t *w25_cacheread(struct w25_dev_s *priv,
                                  off_t sector);
static void w25_cacheerase(struct w25_dev_s *priv,
                           off_t sector);
static void w25_cachewrite(FAR struct w25_dev_s *priv,
                           FAR const uint8_t *buffer,
                           off_t sector, size_t nsectors);
#endif

/* MTD driver methods */

static int w25_erase(FAR struct mtd_dev_s *dev,
                     off_t startblock,
                     size_t nblocks);
static ssize_t w25_bread(FAR struct mtd_dev_s *dev,
                         off_t startblock,
                         size_t nblocks,
                         FAR uint8_t *buf);
static ssize_t w25_bwrite(FAR struct mtd_dev_s *dev,
                          off_t startblock,
                          size_t nblocks,
                          FAR const uint8_t *buf);
static ssize_t w25_read(FAR struct mtd_dev_s *dev,
                        off_t offset,
                        size_t nbytes,
                        FAR uint8_t *buffer);
static int w25_ioctl(FAR struct mtd_dev_s *dev,
                     int cmd,
                     unsigned long arg);
#if defined(CONFIG_MTD_BYTE_WRITE) && !defined(CONFIG_W25_READONLY)
static ssize_t w25_write(FAR struct mtd_dev_s *dev,
                         off_t offset,
                         size_t nbytes,
                         FAR const uint8_t *buffer);
#endif

/****************************************************************************
 * Private Data
 ****************************************************************************/

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Name: w25_lock
 ****************************************************************************/

static void w25_lock(FAR struct spi_dev_s *spi)
{
  /* On SPI buses where there are multiple devices, it will be necessary to
   * lock SPI to have exclusive access to the buses for a sequence of
   * transfers.  The bus should be locked before the chip is selected.
   *
   * This is a blocking call and will not return until we have exclusive
   * access to the SPI bus.
   * We will retain that exclusive access until the bus is unlocked.
   */

  SPI_LOCK(spi, true);

  /* After locking the SPI bus, the we also need call the setfrequency,
   * setbits, and setmode methods to make sure that the SPI is properly
   * configured for the device.
   * If the SPI bus is being shared, then it may have been left in an
   * incompatible state.
   */

  SPI_SETMODE(spi, CONFIG_W25_SPIMODE);
  SPI_SETBITS(spi, 8);
  SPI_HWFEATURES(spi, 0);
  SPI_SETFREQUENCY(spi, CONFIG_W25_SPIFREQUENCY);
}

/****************************************************************************
 * Name: w25_unlock
 ****************************************************************************/

static inline void w25_unlock(FAR struct spi_dev_s *spi)
{
  SPI_LOCK(spi, false);
}

/****************************************************************************
 * Name: w25_readid
 ****************************************************************************/

static inline int w25_readid(struct w25_dev_s *priv)
{
  uint16_t manufacturer;
  uint16_t memory;
  uint16_t capacity;

  w25_finfo("priv: %p\n", priv);

  /* Lock and configure the SPI bus */

  w25_lock(priv->spi);

  /* Wait for any preceding write or erase operation to complete. */

  w25_waitwritecomplete(priv);

  /* Select this FLASH part. */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), true);

  /* Send the "Read ID (RDID)" command and read the first three ID bytes */

  SPI_SEND(priv->spi, W25_JEDEC_ID);
  manufacturer = SPI_SEND(priv->spi, W25_DUMMY);
  memory       = SPI_SEND(priv->spi, W25_DUMMY);
  capacity     = SPI_SEND(priv->spi, W25_DUMMY);

  /* Deselect the FLASH and unlock the bus */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), false);
  w25_unlock(priv->spi);

  w25_finfo("manufacturer: %02x memory: %02x capacity: %02x\n",
        manufacturer, memory, capacity);

  /* Check for a valid manufacturer and memory type */

  if ((manufacturer == W25_JEDEC_WINBOND  ||
       manufacturer == W25_JEDEC_AMIC)    &&
      (memory == W25X_JEDEC_MEMORY_TYPE   ||
       memory == W25Q_JEDEC_MEMORY_TYPE_A ||
       memory == W25Q_JEDEC_MEMORY_TYPE_B ||
       memory == W25Q_JEDEC_MEMORY_TYPE_C ||
       memory == W25Q_JEDEC_MEMORY_TYPE_D))
    {
      /* Okay.. is it a FLASH capacity that we understand? If so, save
       * the FLASH capacity.
       */

      /* 2M-bit / 256K-byte
       *
       * W25Q20CL
       */

      if (capacity == W25_JEDEC_CAPACITY_2MBIT)
        {
           priv->nsectors = NSECTORS_2MBIT;
        }

      /* 8M-bit / 1M-byte
       *
       * W25Q80BV
       */

      else if (capacity == W25_JEDEC_CAPACITY_8MBIT)
        {
           priv->nsectors = NSECTORS_8MBIT;
        }

      /* 16M-bit / 2M-byte (2,097,152)
       *
       * W24X16, W25Q16BV, W25Q16CL, W25Q16CV, W25Q16DW
       */

      else if (capacity == W25_JEDEC_CAPACITY_16MBIT)
        {
           priv->nsectors = NSECTORS_16MBIT;
        }

      /* 32M-bit / 4M-byte (4,194,304)
       *
       * W25X32, W25Q32BV, W25Q32DW
       */

      else if (capacity == W25_JEDEC_CAPACITY_32MBIT)
        {
           priv->nsectors = NSECTORS_32MBIT;
        }

      /* 64M-bit / 8M-byte (8,388,608)
       *
       * W25X64,  W25Q64BV, W25Q64CV, W25Q64DW
       */

      else if (capacity == W25_JEDEC_CAPACITY_64MBIT)
        {
           priv->nsectors = NSECTORS_64MBIT;
        }

      /* 128M-bit / 16M-byte (16,777,216)
       *
       * W25Q128BV
       */

      else if (capacity == W25_JEDEC_CAPACITY_128MBIT)
        {
           priv->nsectors = NSECTORS_128MBIT;
        }
      else
        {
          /* Nope.. we don't understand this capacity. */

          w25_ferr("ERROR: Unsupported capacity: %02x\n", capacity);
          return -ENODEV;
        }

      return OK;
    }

  /* We don't understand the manufacturer or the memory type */

  w25_ferr("ERROR: Unrecognized manufacturer/memory type: %02x/%02x\n",
       manufacturer, memory);
  return -ENODEV;
}

/****************************************************************************
 * Name: w25_unprotect
 ****************************************************************************/

#ifndef CONFIG_W25_READONLY
static void w25_unprotect(FAR struct w25_dev_s *priv)
{
  /* Lock and configure the SPI bus */

  w25_lock(priv->spi);

  /* Wait for any preceding write or erase operation to complete. */

  w25_waitwritecomplete(priv);

  /* Send "Write enable (WREN)" */

  w25_wren(priv);

  /* Select this FLASH part */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), true);

  /* Send "Write enable status (EWSR)" */

  SPI_SEND(priv->spi, W25_WRSR);

  /* Following by the new status value */

  SPI_SEND(priv->spi, 0);
  SPI_SEND(priv->spi, 0);

  /* Deselect the FLASH and unlock the bus */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), false);
  w25_unlock(priv->spi);
}
#endif

/****************************************************************************
 * Name: w25_waitwritecomplete
 ****************************************************************************/

static uint8_t w25_waitwritecomplete(struct w25_dev_s *priv)
{
  uint8_t status;

  /* Loop as long as the memory is busy with a write cycle. Device sets BUSY
   * flag to a 1 state whhen previous write or erase command is still
   * executing and during this time, device will ignore further instructions
   * except for "Read Status Register" and "Erase/Program Suspend"
   * instructions.
   */

  do
    {
      /* Select this FLASH part */

      SPI_SELECT(priv->spi, SPIDEV_FLASH(0), true);

      /* Send "Read Status Register (RDSR)" command */

      SPI_SEND(priv->spi, W25_RDSR);

      /* Send a dummy byte to generate the clock needed to shift out the
       * status
       */

      status = SPI_SEND(priv->spi, W25_DUMMY);

      /* Deselect the FLASH */

      SPI_SELECT(priv->spi, SPIDEV_FLASH(0), false);

      /* Given that writing could take up to few tens of milliseconds, and
       * erasing could take more.  The following short delay in the "busy"
       * case will allow other peripherals to access the SPI bus.
       * Delay would slow down writing too much, so go to sleep only if
       * previous operation was not a page program operation.
       */

      if (priv->prev_instr != W25_PP && (status & W25_SR_BUSY) != 0)
        {
          w25_unlock(priv->spi);
          nxsig_usleep(1000);
          w25_lock(priv->spi);
        }
    }
  while ((status & W25_SR_BUSY) != 0);

  return status;
}

/****************************************************************************
 * Name:  w25_wren
 ****************************************************************************/

static inline void w25_wren(struct w25_dev_s *priv)
{
  /* Select this FLASH part */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), true);

  /* Send "Write Enable (WREN)" command */

  SPI_SEND(priv->spi, W25_WREN);

  /* Deselect the FLASH */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), false);
}

/****************************************************************************
 * Name:  w25_wrdi
 ****************************************************************************/

static inline void w25_wrdi(struct w25_dev_s *priv)
{
  /* Select this FLASH part */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), true);

  /* Send "Write Disable (WRDI)" command */

  SPI_SEND(priv->spi, W25_WRDI);

  /* Deselect the FLASH */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), false);
}

/****************************************************************************
 * Name:  w25_is_erased
 ****************************************************************************/

static bool w25_is_erased(struct w25_dev_s *priv, off_t address, off_t size)
{
  size_t npages = size >> W25_PAGE_SHIFT;
  uint32_t erased_32;
  unsigned int i;
  uint32_t *buf;

  DEBUGASSERT((address % W25_PAGE_SIZE) == 0);
  DEBUGASSERT((size % W25_PAGE_SIZE) == 0);

  buf = kmm_malloc(W25_PAGE_SIZE);
  if (!buf)
    {
      return false;
    }

  memset(&erased_32, W25_ERASED_STATE, sizeof(erased_32));

  /* Walk all pages in given area. */

  while (npages)
    {
      /* Check if all bytes of page is in erased state. */

      w25_byteread(priv, (FAR unsigned char *)buf, address, W25_PAGE_SIZE);

      for (i = 0; i < W25_PAGE_SIZE / sizeof(uint32_t); i++)
        {
          if (buf[i] != erased_32)
            {
              /* Page not in erased state! */

              kmm_free(buf);
              return false;
            }
        }

      address += W25_PAGE_SIZE;
      npages--;
    }

  kmm_free(buf);
  return true;
}

/****************************************************************************
 * Name:  w25_sectorerase
 ****************************************************************************/

static void w25_sectorerase(struct w25_dev_s *priv, off_t sector)
{
  off_t address = sector << W25_SECTOR_SHIFT;

  w25_finfo("sector: %08lx\n", (long)sector);

  /* Check if sector is already erased. */

  if (w25_is_erased(priv, address, W25_SECTOR_SIZE))
    {
      /* Sector already in erased state, so skip erase. */

      return;
    }

  /* Wait for any preceding write or erase operation to complete. */

  w25_waitwritecomplete(priv);

  /* Send write enable instruction */

  w25_wren(priv);

  /* Select this FLASH part */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), true);

  /* Send the "Sector Erase (SE)" instruction */

  SPI_SEND(priv->spi, W25_SE);
  priv->prev_instr = W25_SE;

  /* Send the sector address high byte first. Only the most significant bits
   * (those corresponding to the sector) have any meaning.
   */

  SPI_SEND(priv->spi, (address >> 16) & 0xff);
  SPI_SEND(priv->spi, (address >> 8) & 0xff);
  SPI_SEND(priv->spi, address & 0xff);

  /* Deselect the FLASH */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), false);
}

/****************************************************************************
 * Name:  w25_chiperase
 ****************************************************************************/

static inline int w25_chiperase(struct w25_dev_s *priv)
{
  w25_finfo("priv: %p\n", priv);

  /* Wait for any preceding write or erase operation to complete. */

  w25_waitwritecomplete(priv);

  /* Send write enable instruction */

  w25_wren(priv);

  /* Select this FLASH part */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), true);

  /* Send the "Chip Erase (CE)" instruction */

  SPI_SEND(priv->spi, W25_CE);
  priv->prev_instr = W25_CE;

  /* Deselect the FLASH */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), false);
  w25_finfo("Return: OK\n");
  return OK;
}

/****************************************************************************
 * Name: w25_byteread
 ****************************************************************************/

static void w25_byteread(FAR struct w25_dev_s *priv, FAR uint8_t *buffer,
                           off_t address, size_t nbytes)
{
  uint8_t status;

  w25_finfo("address: %08lx nbytes: %d\n", (long)address, (int)nbytes);

  /* Wait for any preceding write or erase operation to complete. */

  status = w25_waitwritecomplete(priv);
  DEBUGASSERT((status & (W25_SR_WEL | W25_SR_BP_MASK)) == 0);

  /* Make sure that writing is disabled */

  w25_wrdi(priv);

  /* Select this FLASH part */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), true);

  /* Send "Read from Memory " instruction */

#ifdef CONFIG_W25_SLOWREAD
  SPI_SEND(priv->spi, W25_RDDATA);
  priv->prev_instr = W25_RDDATA;
#else
  SPI_SEND(priv->spi, W25_FRD);
  priv->prev_instr = W25_FRD;
#endif

  /* Send the address high byte first. */

  SPI_SEND(priv->spi, (address >> 16) & 0xff);
  SPI_SEND(priv->spi, (address >> 8) & 0xff);
  SPI_SEND(priv->spi, address & 0xff);

  /* Send a dummy byte */

#ifndef CONFIG_W25_SLOWREAD
  SPI_SEND(priv->spi, W25_DUMMY);
#endif

  /* Then read all of the requested bytes */

  SPI_RECVBLOCK(priv->spi, buffer, nbytes);

  /* Deselect the FLASH */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), false);
}

/****************************************************************************
 * Name:  w25_pagewrite
 ****************************************************************************/

#ifndef CONFIG_W25_READONLY
static void w25_pagewrite(struct w25_dev_s *priv, FAR const uint8_t *buffer,
                          off_t address, size_t nbytes)
{
  uint8_t status;

  w25_finfo("address: %08lx nwords: %d\n", (long)address, (int)nbytes);
  DEBUGASSERT(priv && buffer && (address & 0xff) == 0 &&
             (nbytes & 0xff) == 0);

  for (; nbytes > 0; nbytes -= W25_PAGE_SIZE)
    {
      /* Wait for any preceding write or erase operation to complete. */

      status = w25_waitwritecomplete(priv);
      DEBUGASSERT((status & (W25_SR_WEL | W25_SR_BP_MASK)) == 0);

      /* Enable write access to the FLASH */

      w25_wren(priv);

      /* Select this FLASH part */

      SPI_SELECT(priv->spi, SPIDEV_FLASH(0), true);

      /* Send the "Page Program (W25_PP)" Command */

      SPI_SEND(priv->spi, W25_PP);
      priv->prev_instr = W25_PP;

      /* Send the address high byte first. */

      SPI_SEND(priv->spi, (address >> 16) & 0xff);
      SPI_SEND(priv->spi, (address >> 8) & 0xff);
      SPI_SEND(priv->spi, address & 0xff);

      /* Then send the page of data */

      SPI_SNDBLOCK(priv->spi, buffer, W25_PAGE_SIZE);

      /* Deselect the FLASH and setup for the next pass through the loop */

      SPI_SELECT(priv->spi, SPIDEV_FLASH(0), false);

      /* Update addresses */

      address += W25_PAGE_SIZE;
      buffer  += W25_PAGE_SIZE;
    }

  /* Disable writing */

  w25_wrdi(priv);
}
#endif

/****************************************************************************
 * Name:  w25_bytewrite
 ****************************************************************************/

#if defined(CONFIG_MTD_BYTE_WRITE) && !defined(CONFIG_W25_READONLY)
static inline void w25_bytewrite(struct w25_dev_s *priv,
                                 FAR const uint8_t *buffer,
                                 off_t offset,
                                 uint16_t count)
{
  w25_finfo("offset: %08lx  count:%d\n", (long)offset, count);

  /* Wait for any preceding write to complete.  We could simplify things by
   * perform this wait at the end of each write operation (rather than at
   * the beginning of ALL operations), but have the wait first will slightly
   * improve performance.
   */

  w25_waitwritecomplete(priv);

  /* Enable the write access to the FLASH */

  w25_wren(priv);

  /* Select this FLASH part */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), true);

  /* Send "Page Program (PP)" command */

  SPI_SEND(priv->spi, W25_PP);
  priv->prev_instr = W25_PP;

  /* Send the page offset high byte first. */

  SPI_SEND(priv->spi, (offset >> 16) & 0xff);
  SPI_SEND(priv->spi, (offset >> 8) & 0xff);
  SPI_SEND(priv->spi, offset & 0xff);

  /* Then write the specified number of bytes */

  SPI_SNDBLOCK(priv->spi, buffer, count);

  /* Deselect the FLASH: Chip Select high */

  SPI_SELECT(priv->spi, SPIDEV_FLASH(0), false);
  w25_finfo("Written\n");
}
#endif /* defined(CONFIG_MTD_BYTE_WRITE) && !defined(CONFIG_W25_READONLY) */

/****************************************************************************
 * Name: w25_cacheflush
 ****************************************************************************/

#if defined(CONFIG_W25_SECTOR512) && !defined(CONFIG_W25_READONLY)
static void w25_cacheflush(struct w25_dev_s *priv)
{
  /* If the cached is dirty (meaning that it no longer matches the old FLASH
   * contents) or was erased (with the cache containing the correct FLASH
   * contents), then write the cached erase block to FLASH.
   */

  if (IS_DIRTY(priv) || IS_ERASED(priv))
    {
      /* Write entire erase block to FLASH */

      w25_pagewrite(priv, priv->sector,
                   (off_t)priv->esectno << W25_SECTOR_SHIFT,
                    W25_SECTOR_SIZE);

      /* The case is no long dirty and the FLASH is no longer erased */

      CLR_DIRTY(priv);
      CLR_ERASED(priv);
    }
}
#endif

/****************************************************************************
 * Name: w25_cacheread
 ****************************************************************************/

#if defined(CONFIG_W25_SECTOR512) && !defined(CONFIG_W25_READONLY)
static FAR uint8_t *w25_cacheread(struct w25_dev_s *priv, off_t sector)
{
  off_t esectno;
  int   shift;
  int   index;

  /* Convert from the 512 byte sector to the erase sector size of the device.
   * For exmample, if the actual erase sector size if 4Kb (1 << 12), then we
   * first shift to the right by 3 to get the sector number in 4096
   * increments.
   */

  shift   = W25_SECTOR_SHIFT - W25_SECTOR512_SHIFT;
  esectno = sector >> shift;
  w25_finfo("sector: %ld esectno: %d shift=%d\n", sector, esectno, shift);

  /* Check if the requested erase block is already in the cache */

  if (!IS_VALID(priv) || esectno != priv->esectno)
    {
      /* No.. Flush any dirty erase block currently in the cache */

      w25_cacheflush(priv);

      /* Read the erase block into the cache */

      w25_byteread(priv, priv->sector, (esectno << W25_SECTOR_SHIFT),
                   W25_SECTOR_SIZE);

      /* Mark the sector as cached */

      priv->esectno = esectno;

      SET_VALID(priv);          /* The data in the cache is valid */
      CLR_DIRTY(priv);          /* It should match the FLASH contents */
      CLR_ERASED(priv);         /* The underlying FLASH has not been erased */
    }

  /* Get the index to the 512 sector in the erase block that holds the
   * argument
   */

  index = sector & ((1 << shift) - 1);

  /* Return the address in the cache that holds this sector */

  return &priv->sector[index << W25_SECTOR512_SHIFT];
}
#endif

/****************************************************************************
 * Name: w25_cacheerase
 ****************************************************************************/

#if defined(CONFIG_W25_SECTOR512) && !defined(CONFIG_W25_READONLY)
static void w25_cacheerase(struct w25_dev_s *priv, off_t sector)
{
  FAR uint8_t *dest;

  /* First, make sure that the erase block containing the 512 byte sector is
   * in the cache.
   */

  dest = w25_cacheread(priv, sector);

  /* Erase the block containing this sector if it is not already erased.
   * The erased indicated will be cleared when the data from the erase
   * sector is read into the cache and set here when we erase the block.
   */

  if (!IS_ERASED(priv))
    {
      off_t esectno  = sector >> (W25_SECTOR_SHIFT - W25_SECTOR512_SHIFT);
      w25_finfo("sector: %ld esectno: %d\n", sector, esectno);

      w25_sectorerase(priv, esectno);
      SET_ERASED(priv);
    }

  /* Put the cached sector data into the erase state and mart the cache as
   * dirty (but don't update the FLASH yet.
   * The caller will do that at a more optimal time).
   */

  memset(dest, W25_ERASED_STATE, W25_SECTOR512_SIZE);
  SET_DIRTY(priv);
}
#endif

/****************************************************************************
 * Name: w25_cachewrite
 ****************************************************************************/

#if defined(CONFIG_W25_SECTOR512) && !defined(CONFIG_W25_READONLY)
static void w25_cachewrite(FAR struct w25_dev_s *priv,
                           FAR const uint8_t *buffer,
                           off_t sector,
                           size_t nsectors)
{
  FAR uint8_t *dest;

  for (; nsectors > 0; nsectors--)
    {
      /* First, make sure that the erase block containing 512 byte sector is
       * in memory.
       */

      dest = w25_cacheread(priv, sector);

      /* Erase the block containing this sector if it is not already erased.
       * The erased indicated will be cleared when the data from the erase
       * sector is read into the cache and set here when we erase the sector.
       */

      if (!IS_ERASED(priv))
        {
          off_t esectno  = sector >>
                           (W25_SECTOR_SHIFT - W25_SECTOR512_SHIFT);
          w25_finfo("sector: %ld esectno: %d\n", sector, esectno);

          w25_sectorerase(priv, esectno);
          SET_ERASED(priv);
        }

      /* Copy the new sector data into cached erase block */

      memcpy(dest, buffer, W25_SECTOR512_SIZE);
      SET_DIRTY(priv);

      /* Set up for the next 512 byte sector */

      buffer += W25_SECTOR512_SIZE;
      sector++;
    }

  /* Flush the last erase block left in the cache */

  w25_cacheflush(priv);
}
#endif

/****************************************************************************
 * Name: w25_erase
 ****************************************************************************/

static int w25_erase(FAR struct mtd_dev_s *dev,
                     off_t startblock,
                     size_t nblocks)
{
#ifdef CONFIG_W25_READONLY
  return -EACCES;
#else
  FAR struct w25_dev_s *priv = (FAR struct w25_dev_s *)dev;
  size_t blocksleft = nblocks;

  w25_finfo("startblock: %08lx nblocks: %d\n", (long)startblock,
                                          (int)nblocks);

  /* Lock access to the SPI bus until we complete the erase */

  w25_lock(priv->spi);

  while (blocksleft-- > 0)
    {
      /* Erase each sector */

#ifdef CONFIG_W25_SECTOR512
      w25_cacheerase(priv, startblock);
#else
      w25_sectorerase(priv, startblock);
#endif
      startblock++;
    }

#ifdef CONFIG_W25_SECTOR512
  /* Flush the last erase block left in the cache */

  w25_cacheflush(priv);
#endif

  w25_unlock(priv->spi);
  return (int)nblocks;
#endif
}

/****************************************************************************
 * Name: w25_bread
 ****************************************************************************/

static ssize_t w25_bread(FAR struct mtd_dev_s *dev,
                         off_t startblock,
                         size_t nblocks,
                         FAR uint8_t *buffer)
{
  ssize_t nbytes;

  w25_finfo("startblock: %08lx nblocks: %d\n",
       (long)startblock, (int)nblocks);

  /* On this device, we can handle the block read just like the byte-oriented
   * read
   */

#ifdef CONFIG_W25_SECTOR512
  nbytes = w25_read(dev, startblock << W25_SECTOR512_SHIFT,
                    nblocks << W25_SECTOR512_SHIFT, buffer);
  if (nbytes > 0)
    {
      nbytes >>= W25_SECTOR512_SHIFT;
    }

#else
  nbytes = w25_read(dev, startblock << W25_PAGE_SHIFT,
                    nblocks << W25_PAGE_SHIFT, buffer);
  if (nbytes > 0)
    {
      nbytes >>= W25_PAGE_SHIFT;
    }
#endif

  return nbytes;
}

/****************************************************************************
 * Name: w25_bwrite
 ****************************************************************************/

static ssize_t w25_bwrite(FAR struct mtd_dev_s *dev, off_t startblock,
                          size_t nblocks, FAR const uint8_t *buffer)
{
#ifdef CONFIG_W25_READONLY
  return -EACCESS;
#else
  FAR struct w25_dev_s *priv = (FAR struct w25_dev_s *)dev;

  w25_finfo("startblock: %08lx nblocks: %d\n", (long)startblock,
                                                  (int)nblocks);

  /* Lock the SPI bus and write all of the pages to FLASH */

  w25_lock(priv->spi);

#if defined(CONFIG_W25_SECTOR512)
  w25_cachewrite(priv, buffer, startblock, nblocks);
#else
  w25_pagewrite(priv, buffer, startblock << W25_PAGE_SHIFT,
                  nblocks << W25_PAGE_SHIFT);
#endif
  w25_unlock(priv->spi);

  return nblocks;
#endif
}

/****************************************************************************
 * Name: w25_read
 ****************************************************************************/

static ssize_t w25_read(FAR struct mtd_dev_s *dev,
                        off_t offset,
                        size_t nbytes,
                        FAR uint8_t *buffer)
{
  FAR struct w25_dev_s *priv = (FAR struct w25_dev_s *)dev;

  w25_finfo("offset: %08lx nbytes: %d\n", (long)offset, (int)nbytes);

  /* Lock the SPI bus and select this FLASH part */

  w25_lock(priv->spi);
  w25_byteread(priv, buffer, offset, nbytes);
  w25_unlock(priv->spi);

  w25_finfo("return nbytes: %d\n", (int)nbytes);
  return nbytes;
}

/****************************************************************************
 * Name: w25_write
 ****************************************************************************/

#if defined(CONFIG_MTD_BYTE_WRITE) && !defined(CONFIG_W25_READONLY)
static ssize_t w25_write(FAR struct mtd_dev_s *dev,
                         off_t offset,
                         size_t nbytes,
                         FAR const uint8_t *buffer)
{
  FAR struct w25_dev_s *priv = (FAR struct w25_dev_s *)dev;
  int    startpage;
  int    endpage;
  int    count;
  int    index;
  int    bytestowrite;

  w25_finfo("offset: %08lx nbytes: %d\n", (long)offset, (int)nbytes);

  /* We must test if the offset + count crosses one or more pages
   * and perform individual writes.  The devices can only write in
   * page increments.
   */

  startpage = offset / W25_PAGE_SIZE;
  endpage = (offset + nbytes) / W25_PAGE_SIZE;

  w25_lock(priv->spi);
  if (startpage == endpage)
    {
      /* All bytes within one programmable page.  Just do the write. */

      w25_bytewrite(priv, buffer, offset, nbytes);
    }
  else
    {
      /* Write the 1st partial-page */

      count = nbytes;
      bytestowrite = W25_PAGE_SIZE - (offset & (W25_PAGE_SIZE - 1));
      w25_bytewrite(priv, buffer, offset, bytestowrite);

      /* Update offset and count */

      offset += bytestowrite;
      count -=  bytestowrite;
      index = bytestowrite;

      /* Write full pages */

      while (count >= W25_PAGE_SIZE)
        {
          w25_bytewrite(priv, &buffer[index], offset, W25_PAGE_SIZE);

          /* Update offset and count */

          offset += W25_PAGE_SIZE;
          count -= W25_PAGE_SIZE;
          index += W25_PAGE_SIZE;
        }

      /* Now write any partial page at the end */

      if (count > 0)
        {
          w25_bytewrite(priv, &buffer[index], offset, count);
        }
    }

  w25_unlock(priv->spi);
  return nbytes;
}
#endif /* defined(CONFIG_MTD_BYTE_WRITE) && !defined(CONFIG_W25_READONLY) */

/****************************************************************************
 * Name: w25_ioctl
 ****************************************************************************/

static int w25_ioctl(FAR struct mtd_dev_s *dev, int cmd, unsigned long arg)
{
  FAR struct w25_dev_s *priv = (FAR struct w25_dev_s *)dev;
  int ret = -EINVAL; /* Assume good command with bad parameters */

  w25_finfo("cmd: %d\n", cmd);

  switch (cmd)
    {
      case MTDIOC_GEOMETRY:
        {
          FAR struct mtd_geometry_s *geo =
            (FAR struct mtd_geometry_s *)((uintptr_t)arg);
          if (geo)
            {
              memset(geo, 0, sizeof(*geo));

              /* Populate the geometry structure with information need to
               * know the capacity and how to access the device.
               *
               * NOTE:
               * that the device is treated as though it where just an array
               * of fixed size blocks. That is most likely not true, but the
               * client will expect the device logic to do whatever is
               * necessary to make it appear so.
               */

#ifdef CONFIG_W25_SECTOR512
              geo->blocksize    = (1 << W25_SECTOR512_SHIFT);
              geo->erasesize    = (1 << W25_SECTOR512_SHIFT);
              geo->neraseblocks = priv->nsectors <<
                                  (W25_SECTOR_SHIFT - W25_SECTOR512_SHIFT);
#else
              geo->blocksize    = W25_PAGE_SIZE;
              geo->erasesize    = W25_SECTOR_SIZE;
              geo->neraseblocks = priv->nsectors;
#endif
              ret               = OK;

              w25_finfo("blocksize: %" PRIu32 " erasesize: %" PRIu32
                    " neraseblocks: %" PRIu32 "\n",
                    geo->blocksize, geo->erasesize, geo->neraseblocks);
            }
        }
        break;

      case BIOC_PARTINFO:
        {
          FAR struct partition_info_s *info =
            (FAR struct partition_info_s *)arg;
          if (info != NULL)
            {
#ifdef CONFIG_W25_SECTOR512
              info->numsectors  = priv->nsectors <<
                                  (W25_SECTOR_SHIFT - W25_SECTOR512_SHIFT);
              info->sectorsize  = 1 << W25_SECTOR512_SHIFT;
#else
              info->numsectors  = priv->nsectors *
                                  W25_SECTOR_SIZE / W25_PAGE_SIZE;
              info->sectorsize  = W25_PAGE_SIZE;
#endif
              info->startsector = 0;
              info->parent[0]   = '\0';
              ret               = OK;
            }
        }
        break;

      case MTDIOC_BULKERASE:
        {
            /* Erase the entire device */

            w25_lock(priv->spi);
            ret = w25_chiperase(priv);
            w25_unlock(priv->spi);
        }
        break;

      case MTDIOC_ERASESTATE:
        {
          FAR uint8_t *result = (FAR uint8_t *)arg;
          *result = W25_ERASED_STATE;

          ret = OK;
        }
        break;

      default:
        ret = -ENOTTY; /* Bad command */
        break;
    }

  w25_finfo("return %d\n", ret);
  return ret;
}

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: w25_initialize
 *
 * Description:
 *   Create an initialize MTD device instance. MTD devices are not registered
 *   in the file system, but are created as instances that can be bound to
 *   other functions (such as a block or character driver front end).
 *
 ****************************************************************************/

FAR struct mtd_dev_s *w25_initialize(FAR struct spi_dev_s *spi)
{
  FAR struct w25_dev_s *priv;
  int ret;

  w25_finfo("spi: %p\n", spi);

  /* Allocate a state structure (we allocate the structure instead of using
   * a fixed, static allocation so that we can handle multiple FLASH devices.
   * The current implementation would handle only one FLASH part per SPI
   * device (only because of the SPIDEV_FLASH(0) definition) and so would
   * have to be extended to handle multiple FLASH parts on the same SPI bus.
   */

  priv = kmm_zalloc(sizeof(struct w25_dev_s));
  if (priv)
    {
      /* Initialize the allocated structure (unsupported methods were
       * nullified by kmm_zalloc).
       */

      priv->mtd.erase  = w25_erase;
      priv->mtd.bread  = w25_bread;
      priv->mtd.bwrite = w25_bwrite;
      priv->mtd.read   = w25_read;
      priv->mtd.ioctl  = w25_ioctl;
#if defined(CONFIG_MTD_BYTE_WRITE) && !defined(CONFIG_W25_READONLY)
      priv->mtd.write  = w25_write;
#endif
      priv->mtd.name   = "w25";
      priv->spi        = spi;

      /* Deselect the FLASH */

      SPI_SELECT(spi, SPIDEV_FLASH(0), false);

      /* Identify the FLASH chip and get its capacity */

      ret = w25_readid(priv);
      if (ret != OK)
        {
          /* Unrecognized! Discard all of that work we just did and
           * return NULL
           */

          w25_ferr("ERROR: Unrecognized\n");
          kmm_free(priv);
          return NULL;
        }
      else
        {
          /* Make sure that the FLASH is unprotected so that we can write
           * into it.
           */

#ifndef CONFIG_W25_READONLY
          w25_unprotect(priv);
#endif

#ifdef CONFIG_W25_SECTOR512        /* Simulate a 512 byte sector */
          /* Allocate a buffer for the erase block cache */

          priv->sector = kmm_malloc(W25_SECTOR_SIZE);
          if (!priv->sector)
            {
              /* Discard all of that work we just did and return NULL */

              w25_ferr("ERROR: Allocation failed\n");
              kmm_free(priv);
              return NULL;
            }
#endif
        }
    }

  /* Return the implementation-specific state structure as the MTD device */

  w25_finfo("Return %p\n", priv);
  return (FAR struct mtd_dev_s *)priv;
}