SST25L (non JEDEC) SPI Flash driver

Add support for the non JEDEC SST25L SPI Flash devices.

Signed-off-by: Andre Renaud <andre@bluewatersys.com>
Signed-off-by: Ryan Mallon <ryan@bluewatersys.com>
---

Hi Ryan,

On Mon, Jun 22, 2009 at 03:58:51PM +1200, Ryan Mallon wrote:
> +static int sst25l_erase_block(struct sst25l_flash *flash, u32 offset)
> +{
> +	u8 command[4];
> +	int err;
> +
> +	err = sst25l_write_enable(flash, 1);

Is this enable/disable strictly required for each write/erase? Can't we just 
enable write once?

> +	if (err)
> +		return err;
> +
> +	command[0] = SST25L_CMD_BLOCK_ERASE;
> +	command[1] = offset >> 16;
> +	command[2] = offset >> 8;
> +	command[3] = offset;
> +	err = spi_write(flash->spi, command, 4);
> +	if (err)
> +		return err;
> +
> +	err = sst25l_wait_till_ready(flash);
> +	if (err)
> +		return err;
> +
> +	return sst25l_write_enable(flash, 0);
> +}

baruch

Baruch Siach wrote:
> Hi Ryan,
> 
> On Mon, Jun 22, 2009 at 03:58:51PM +1200, Ryan Mallon wrote:
>> +static int sst25l_erase_block(struct sst25l_flash *flash, u32 offset)
>> +{
>> +	u8 command[4];
>> +	int err;
>> +
>> +	err = sst25l_write_enable(flash, 1);
> 
> Is this enable/disable strictly required for each write/erase? Can't we just 
> enable write once?

The datasheet says that prior to any write/erase instruction the write
enable instruction must be sent.

~Ryan

On Mon, 2009-06-22 at 15:58 +1200, Ryan Mallon wrote:
> Add support for the non JEDEC SST25L SPI Flash devices.
> 
> Signed-off-by: Andre Renaud <andre@bluewatersys.com>
> Signed-off-by: Ryan Mallon <ryan@bluewatersys.com>
> ---
> 
> diff --git a/drivers/mtd/devices/Kconfig b/drivers/mtd/devices/Kconfig
> index 325fab9..c222514 100644
> --- a/drivers/mtd/devices/Kconfig
> +++ b/drivers/mtd/devices/Kconfig
> @@ -104,6 +104,16 @@ config M25PXX_USE_FAST_READ
>  	help
>  	  This option enables FAST_READ access supported by ST M25Pxx.

Would it please be possible to get rid of this warning:

  CC [M]  drivers/mtd/devices/sst25l.o
drivers/mtd/devices/sst25l.c: In function ‘sst25l_write’:
drivers/mtd/devices/sst25l.c:306: warning: comparison of distinct pointer types lacks a cast

I see it on my x86_64.

2009/6/22 Ryan Mallon <ryan@bluewatersys.com>:

> Add support for the non JEDEC SST25L SPI Flash devices.
>
> Signed-off-by: Andre Renaud <andre@bluewatersys.com>
> Signed-off-by: Ryan Mallon <ryan@bluewatersys.com>
> ---
>
> diff --git a/drivers/mtd/devices/Kconfig b/drivers/mtd/devices/Kconfig
> index 325fab9..c222514 100644
> --- a/drivers/mtd/devices/Kconfig
> +++ b/drivers/mtd/devices/Kconfig
> @@ -104,6 +104,16 @@ config M25PXX_USE_FAST_READ
>        help
>          This option enables FAST_READ access supported by ST M25Pxx.
>
> +config MTD_SST25L
> +       tristate "Support SST25L (non JEDEC) SPI Flash chips"
> +       depends on SPI_MASTER
> +       help
> +         This enables access to the non JEDEC SST25L SPI flash chips, used
> +         for program and data storage.
> +
> +         Set up your spi devices with the right board-specific platform data,
> +         if you want to specify device partitioning.
> +
>  config MTD_SLRAM
>        tristate "Uncached system RAM"
>        help
> diff --git a/drivers/mtd/devices/Makefile b/drivers/mtd/devices/Makefile
> index 0993d5c..ab5c9b9 100644
> --- a/drivers/mtd/devices/Makefile
> +++ b/drivers/mtd/devices/Makefile
> @@ -16,3 +16,4 @@ obj-$(CONFIG_MTD_LART)                += lart.o
>  obj-$(CONFIG_MTD_BLOCK2MTD)    += block2mtd.o
>  obj-$(CONFIG_MTD_DATAFLASH)    += mtd_dataflash.o
>  obj-$(CONFIG_MTD_M25P80)       += m25p80.o
> +obj-$(CONFIG_MTD_SST25L)       += sst25l.o
> diff --git a/drivers/mtd/devices/sst25l.c b/drivers/mtd/devices/sst25l.c
> new file mode 100644
> index 0000000..8e62479
> --- /dev/null
> +++ b/drivers/mtd/devices/sst25l.c
> @@ -0,0 +1,508 @@
> +/*
> + * drivers/mtd/sst25l.c
> + *
> + * Driver for SST25L SPI Flash chips
> + *
> + * Copyright (C) 2009 Bluewater Systems Ltd
> + * Author: Andre Renaud <andre@bluewatersys.com>
> + * Author: Ryan Mallon <ryan@bluewatersys.com>
> + *
> + * Based on m25p80.c
> + *
> + * This code is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + */
> +
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/device.h>
> +#include <linux/mutex.h>
> +#include <linux/math64.h>

I'm always suspicious about drivers doing maths, so I
think this can be removed, see below...

> +#include <linux/interrupt.h>
> +
> +#include <linux/mtd/mtd.h>
> +#include <linux/mtd/partitions.h>
> +
> +#include <linux/spi/spi.h>
> +#include <linux/spi/flash.h>
> +
> +/* Erases can take up to 3 seconds! */
> +#define MAX_READY_WAIT_JIFFIES msecs_to_jiffies(3000)
> +
> +#define SST25L_CMD_WRSR                0x01    /* Write status register */
> +#define SST25L_CMD_WRDI                0x04    /* Write disable */
> +#define SST25L_CMD_RDSR                0x05    /* Read status register */
> +#define SST25L_CMD_WREN                0x06    /* Write enable */
> +#define SST25L_CMD_READ                0x03    /* High speed read */
> +
> +#define SST25L_CMD_EWSR                0x50    /* Enable write status register */
> +#define SST25L_CMD_BLOCK_ERASE 0x52    /* Erase sector */
> +#define SST25L_CMD_READ_ID     0x90    /* Read device ID */
> +#define SST25L_CMD_AAI_PROGRAM 0xaf    /* Auto address increment */
> +
> +#define SST25L_STATUS_BUSY     (1 << 0)        /* Chip is busy */
> +#define SST25L_STATUS_WREN     (1 << 1)        /* Write enabled */
> +#define SST25L_STATUS_BP0      (1 << 2)        /* Block protection 0 */
> +#define SST25L_STATUS_BP1      (1 << 3)        /* Block protection 1 */
> +
> +struct sst25l_flash {
> +       struct spi_device       *spi;
> +       struct mutex            lock;
> +       struct mtd_info         mtd;
> +
> +       int                     partitioned;
> +};
> +
> +struct flash_info {
> +       const char              *name;
> +       u16                     device_id;
> +       unsigned                page_size;
> +       unsigned                nr_pages;
> +       unsigned                erase_size;
> +};
> +
> +#define to_sst25l_flash(x) container_of(x, struct sst25l_flash, mtd)
> +
> +static struct flash_info __devinitdata sst25l_flash_info[] = {

__devinitdata or __initdata?
Check the definitions from include/linux/init.h. If it's hot-pluggable
then it's fine!

> +       {"sst25lf020a", 0xbf43, 256, 1024, 32 * 1024},
> +       {"sst25lf040a", 0xbf44, 256, 2048, 32 * 1024},
> +};
> +
> +static int sst25l_status(struct sst25l_flash *flash, int *status)
> +{
> +       u8 command, response;
> +       int err;
> +
> +       command = SST25L_CMD_RDSR;
> +       err = spi_write_then_read(flash->spi, &command, 1, &response, 1);
> +       if (err < 0)
> +               return err;
> +
> +       *status = response;
> +       return 0;
> +}
> +
> +static int sst25l_write_enable(struct sst25l_flash *flash, int enable)
> +{
> +       u8 command[2];
> +       int status, err;
> +
> +       command[0] = enable ? SST25L_CMD_WREN : SST25L_CMD_WRDI;
> +       err = spi_write(flash->spi, command, 1);
> +       if (err)
> +               return err;
> +
> +       command[0] = SST25L_CMD_EWSR;
> +       err = spi_write(flash->spi, command, 1);
> +       if (err)
> +               return err;
> +
> +       command[0] = SST25L_CMD_WRSR;
> +       command[1] = enable ? 0 : SST25L_STATUS_BP0 | SST25L_STATUS_BP1;
> +       err = spi_write(flash->spi, command, 2);
> +       if (err)
> +               return err;
> +
> +       if (enable) {
> +               err = sst25l_status(flash, &status);
> +               if (err)
> +                       return err;
> +               if (!(status & SST25L_STATUS_WREN))
> +                       return -EROFS;
> +       }
> +
> +       return 0;
> +}
> +
> +static int sst25l_wait_till_ready(struct sst25l_flash *flash)
> +{
> +       unsigned long deadline;
> +       int status, err;
> +
> +       deadline = jiffies + MAX_READY_WAIT_JIFFIES;
> +       do {
> +               err = sst25l_status(flash, &status);
> +               if (err)
> +                       return err;
> +               if (!(status & SST25L_STATUS_BUSY))
> +                       return 0;
> +
> +               cond_resched();
> +       } while (!time_after_eq(jiffies, deadline));
> +
> +       return -ETIMEDOUT;
> +}
> +
> +static int sst25l_erase_block(struct sst25l_flash *flash, u32 offset)
> +{
> +       u8 command[4];
> +       int err;
> +
> +       err = sst25l_write_enable(flash, 1);
> +       if (err)
> +               return err;
> +
> +       command[0] = SST25L_CMD_BLOCK_ERASE;
> +       command[1] = offset >> 16;
> +       command[2] = offset >> 8;
> +       command[3] = offset;
> +       err = spi_write(flash->spi, command, 4);
> +       if (err)
> +               return err;
> +
> +       err = sst25l_wait_till_ready(flash);
> +       if (err)
> +               return err;
> +
> +       return sst25l_write_enable(flash, 0);
> +}
> +
> +static int sst25l_erase(struct mtd_info *mtd, struct erase_info *instr)
> +{
> +       struct sst25l_flash *flash = to_sst25l_flash(mtd);
> +       u32 addr, end, rem;
> +       int err;
> +
> +       /* Sanity checks */
> +       if (instr->addr + instr->len > flash->mtd.size)
> +               return -EINVAL;
> +
> +       div_u64_rem(instr->len, mtd->erasesize, &rem);

if ((instr->len & 0xFFFFFFFFU) % mtd->erasesize)
  return -EINVAL;

> +       if (rem)
> +               return -EINVAL;
> +
> +       div_u64_rem(instr->addr, mtd->erasesize, &rem);

Same thing again.

> +       if (rem)
> +               return -EINVAL;
> +
> +       addr = instr->addr;
> +       end = addr + instr->len;
> +
> +       mutex_lock(&flash->lock);
> +
> +       err = sst25l_wait_till_ready(flash);
> +       if (err)
> +               return err;
> +
> +       while (addr < end) {
> +               err = sst25l_erase_block(flash, addr);
> +               if (err) {
> +                       mutex_unlock(&flash->lock);
> +                       instr->state = MTD_ERASE_FAILED;
> +                       dev_err(&flash->spi->dev, "Erase failed\n");
> +                       return err;
> +               }
> +
> +               addr += mtd->erasesize;
> +       }
> +
> +       mutex_unlock(&flash->lock);
> +
> +       instr->state = MTD_ERASE_DONE;
> +       mtd_erase_callback(instr);
> +       return 0;
> +}
> +
> +static int sst25l_read(struct mtd_info *mtd, loff_t from, size_t len,
> +                      size_t *retlen, u_char *buf)
> +{
> +       struct sst25l_flash *flash = to_sst25l_flash(mtd);
> +       struct spi_transfer transfer[2];
> +       struct spi_message message;
> +       u8 command[4];
> +       int ret;
> +
> +       /* Sanity checking */
> +       if (len == 0)
> +               return 0;
> +
> +       if (from + len > flash->mtd.size)
> +               return -EINVAL;
> +
> +       if (retlen)
> +               *retlen = 0;
> +
> +       spi_message_init(&message);
> +       memset(&transfer, 0, sizeof(transfer));
> +
> +       command[0] = SST25L_CMD_READ;
> +       command[1] = from >> 16;
> +       command[2] = from >> 8;
> +       command[3] = from;
> +
> +       transfer[0].tx_buf = command;
> +       transfer[0].len = sizeof(command);
> +       spi_message_add_tail(&transfer[0], &message);
> +
> +       transfer[1].rx_buf = buf;
> +       transfer[1].len = len;
> +       spi_message_add_tail(&transfer[1], &message);
> +
> +       mutex_lock(&flash->lock);
> +
> +       /* Wait for previous write/erase to complete */
> +       ret = sst25l_wait_till_ready(flash);
> +       if (ret) {
> +               mutex_unlock(&flash->lock);
> +               return ret;
> +       }
> +
> +       spi_sync(flash->spi, &message);
> +
> +       if (retlen && message.actual_length > sizeof(command))
> +               *retlen += message.actual_length - sizeof(command);
> +
> +       mutex_unlock(&flash->lock);
> +       return 0;
> +}
> +
> +static int sst25l_write(struct mtd_info *mtd, loff_t to, size_t len,
> +                       size_t *retlen, const u_char *buf)
> +{
> +       struct sst25l_flash *flash = to_sst25l_flash(mtd);
> +       int i, j, ret, bytes, copied = 0;
> +       u8 command[5];
> +       u32 rem;
> +
> +       /* Sanity checks */
> +       if (!len)
> +               return 0;
> +
> +       if (to + len > flash->mtd.size)
> +               return -EINVAL;
> +
> +       div_u64_rem(to, mtd->writesize, &rem);

I see. But do you really want to do that with maths?
Can't you just do some simple arithmetics since mtd->writesize is
u32 anything in the higher 32 bits can be ignored (it will be
divisible with any u32 value anyway!), so

/* Need to be evenly divisible by writesize */
if ((to & 0xFFFFFFFFU) % mtd->writesize)
    return -EINVAL;

does this work?

> +       if (rem)
> +               return -EINVAL;
> +
> +       mutex_lock(&flash->lock);
> +
> +       ret = sst25l_write_enable(flash, 1);
> +       if (ret)
> +               goto out;
> +
> +       for (i = 0; i < len; i += mtd->writesize) {
> +               ret = sst25l_wait_till_ready(flash);
> +               if (ret)
> +                       goto out;
> +
> +               /* Write the first byte of the page */
> +               command[0] = SST25L_CMD_AAI_PROGRAM;
> +               command[1] = (to + i) >> 16;
> +               command[2] = (to + i) >> 8;
> +               command[3] = (to + i);
> +               command[4] = buf[i];
> +               ret = spi_write(flash->spi, command, 5);
> +               if (ret < 0)
> +                       goto out;
> +               copied++;
> +
> +               /*
> +                * Write the remaining bytes using auto address
> +                * increment mode
> +                */
> +               bytes = min(mtd->writesize, len - i);
> +               for (j = 1; j < bytes; j++, copied++) {
> +                       ret = sst25l_wait_till_ready(flash);
> +                       if (ret)
> +                               goto out;
> +
> +                       command[1] = buf[i + j];
> +                       ret = spi_write(flash->spi, command, 2);
> +                       if (ret)
> +                               goto out;
> +               }
> +       }
> +
> +out:
> +       ret = sst25l_write_enable(flash, 0);
> +
> +       if (retlen)
> +               *retlen = copied;
> +
> +       mutex_unlock(&flash->lock);
> +       return ret;
> +}
> +
> +static struct flash_info *__devinit sst25l_match_device(struct spi_device *spi)

Or is it __init really? NB: this will save (very little) memory on your system.

> +{
> +       struct flash_info *flash_info = NULL;
> +       u8 command[4], response;
> +       int i, err;
> +       u16 id;
> +
> +       command[0] = SST25L_CMD_READ_ID;
> +       command[1] = 0;
> +       command[2] = 0;
> +       command[3] = 0;
> +       err = spi_write_then_read(spi, command, sizeof(command), &response, 1);
> +       if (err < 0) {
> +               dev_err(&spi->dev, "error reading device id msb\n");
> +               return NULL;
> +       }
> +
> +       id = response << 8;
> +
> +       command[0] = SST25L_CMD_READ_ID;
> +       command[1] = 0;
> +       command[2] = 0;
> +       command[3] = 1;
> +       err = spi_write_then_read(spi, command, sizeof(command), &response, 1);
> +       if (err < 0) {
> +               dev_err(&spi->dev, "error reading device id lsb\n");
> +               return NULL;
> +       }
> +
> +       id |= response;
> +
> +       for (i = 0; i < ARRAY_SIZE(sst25l_flash_info); i++)
> +               if (sst25l_flash_info[i].device_id == id)
> +                       flash_info = &sst25l_flash_info[i];
> +
> +       if (!flash_info)
> +               dev_err(&spi->dev, "unknown id %.4x\n", id);
> +
> +       return flash_info;
> +}
> +
> +static int __devinit sst25l_probe(struct spi_device *spi)

Or __init?

> +{
> +       struct flash_info *flash_info;
> +       struct sst25l_flash *flash;
> +       struct flash_platform_data *data;
> +       int i;
> +
> +       flash_info = sst25l_match_device(spi);
> +       if (!flash_info)
> +               return -ENODEV;
> +
> +       flash = kzalloc(sizeof(struct sst25l_flash), GFP_KERNEL);
> +       if (!flash)
> +               return -ENOMEM;
> +
> +       flash->spi = spi;
> +       mutex_init(&flash->lock);
> +       dev_set_drvdata(&spi->dev, flash);
> +
> +       data = spi->dev.platform_data;
> +       if (data && data->name)
> +               flash->mtd.name = data->name;
> +       else
> +               flash->mtd.name = dev_name(&spi->dev);
> +
> +       flash->mtd.type         = MTD_NORFLASH;
> +       flash->mtd.flags        = MTD_CAP_NORFLASH;
> +       flash->mtd.erasesize    = flash_info->erase_size;
> +       flash->mtd.writesize    = flash_info->page_size;
> +       flash->mtd.size         = flash_info->page_size * flash_info->nr_pages;
> +       flash->mtd.erase        = sst25l_erase;
> +       flash->mtd.read         = sst25l_read;
> +       flash->mtd.write        = sst25l_write;
> +
> +       dev_info(&spi->dev, "%s (%lld Kbytes)\n", flash_info->name,
> +                (long long)flash->mtd.size >> 10);
> +
> +       DEBUG(MTD_DEBUG_LEVEL2,
> +             "mtd .name = %s, .size = 0x%llx (%lldMiB) "
> +             ".erasesize = 0x%.8x (%uKiB) .numeraseregions = %d\n",
> +             flash->mtd.name,
> +             (long long)flash->mtd.size, (long long)(flash->mtd.size >> 20),
> +             flash->mtd.erasesize, flash->mtd.erasesize / 1024,
> +             flash->mtd.numeraseregions);
> +
> +       if (flash->mtd.numeraseregions)
> +               for (i = 0; i < flash->mtd.numeraseregions; i++)
> +                       DEBUG(MTD_DEBUG_LEVEL2,
> +                             "mtd.eraseregions[%d] = { .offset = 0x%llx, "
> +                             ".erasesize = 0x%.8x (%uKiB), "
> +                             ".numblocks = %d }\n",
> +                             i, (long long)flash->mtd.eraseregions[i].offset,
> +                             flash->mtd.eraseregions[i].erasesize,
> +                             flash->mtd.eraseregions[i].erasesize / 1024,
> +                             flash->mtd.eraseregions[i].numblocks);
> +
> +       if (mtd_has_partitions()) {
> +               struct mtd_partition *parts = NULL;
> +               int nr_parts = 0;
> +
> +               if (mtd_has_cmdlinepart()) {
> +                       static const char *part_probes[] =
> +                               {"cmdlinepart", NULL};
> +
> +                       nr_parts = parse_mtd_partitions(&flash->mtd,
> +                                                       part_probes,
> +                                                       &parts, 0);
> +               }
> +
> +               if (nr_parts <= 0 && data && data->parts) {
> +                       parts = data->parts;
> +                       nr_parts = data->nr_parts;
> +               }
> +
> +               if (nr_parts > 0) {
> +                       for (i = 0; i < nr_parts; i++) {
> +                               DEBUG(MTD_DEBUG_LEVEL2, "partitions[%d] = "
> +                                     "{.name = %s, .offset = 0x%llx, "
> +                                     ".size = 0x%llx (%lldKiB) }\n",
> +                                     i, parts[i].name,
> +                                     (long long)parts[i].offset,
> +                                     (long long)parts[i].size,
> +                                     (long long)(parts[i].size >> 10));
> +                       }
> +
> +                       flash->partitioned = 1;
> +                       return add_mtd_partitions(&flash->mtd,
> +                                                 parts, nr_parts);
> +               }
> +
> +       } else if (data->nr_parts) {
> +               dev_warn(&spi->dev, "ignoring %d default partitions on %s\n",
> +                        data->nr_parts, data->name);
> +       }
> +
> +       return add_mtd_device(&flash->mtd) == 1 ? -ENODEV : 0;
> +}
> +
> +static int __devexit sst25l_remove(struct spi_device *spi)

Or __exit?

> +{
> +       struct sst25l_flash *flash = dev_get_drvdata(&spi->dev);
> +       int ret;
> +
> +       if (mtd_has_partitions() && flash->partitioned)
> +               ret = del_mtd_partitions(&flash->mtd);
> +       else
> +               ret = del_mtd_device(&flash->mtd);
> +       if (ret == 0)
> +               kfree(flash);
> +       return ret;
> +}
> +
> +static struct spi_driver sst25l_driver = {
> +       .driver = {
> +               .name   = "sst25l",
> +               .bus    = &spi_bus_type,
> +               .owner  = THIS_MODULE,
> +       },
> +       .probe          = sst25l_probe,
> +       .remove         = __devexit_p(sst25l_remove),

Or __exit_p()?

> +};
> +
> +static int __init sst25l_init(void)
> +{
> +       return spi_register_driver(&sst25l_driver);
> +}
> +
> +static void __exit sst25l_exit(void)
> +{
> +       spi_unregister_driver(&sst25l_driver);
> +}
> +
> +module_init(sst25l_init);
> +module_exit(sst25l_exit);
> +
> +MODULE_DESCRIPTION("MTD SPI driver for SST25L Flash chips");
> +MODULE_AUTHOR("Andre Renaud <andre@bluewatersys.com>, "
> +             "Ryan Mallon <ryan@bluewatersys.com>");
> +MODULE_LICENSE("GPL");
>
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Yours,
Linus Walleij

On Sunday, June 21, 2009 8:59 PM, Ryan Mallon wrote:
>
> Add support for the non JEDEC SST25L SPI Flash devices.
>
> Signed-off-by: Andre Renaud <andre@bluewatersys.com>
> Signed-off-by: Ryan Mallon <ryan@bluewatersys.com>

> +struct flash_info {
> +	const char		*name;
> +	u16			device_id;
> +	unsigned		page_size;
> +	unsigned		nr_pages;
> +	unsigned		erase_size;
> +};
> +
> +#define to_sst25l_flash(x) container_of(x, struct sst25l_flash, mtd)
> +
> +static struct flash_info __devinitdata sst25l_flash_info[] = {
> +	{"sst25lf020a", 0xbf43, 256, 1024, 32 * 1024},
> +	{"sst25lf040a",	0xbf44,	256, 2048, 32 * 1024},
> +};
> +

Ryan,

I finally got a chance to test this on my hardware.  Previously
I was using a hacked version on the m25p80 driver to access the
SST23LF020A on my board.

The driver works fine but you are only supporting the block erase,
SST25L_CMD_BLOCK_ERASE (opcode 0x52).  The SST25L chips also can do a
sector erase (opcode 0x20) and a full chip erase (opcode 0x60).

The full chip erase is not that important but might give a slight
performance increase on larger devices.  Max block erase time is
listed as 25ms at 25MHz in the datasheet.  The SST25LF020A contains
8 blocks so it's "typical" full chip erase time should be around
200ms.  For comparison, the chip erase time is listed as 100ms.

The sector erase is a bigger deal.  On the EDB93xx boards one of the
SPI flash uses is used to store the MAC address at offset 0x2000 (4K
offset).  The board can also be configured to boot from offset 0x0000
in the SPI flash.  This basically gives the user a three partition
setup:

static struct mtd_partition edb93xx_spi_flash_partitions[] = {
	{
		.name	= "SPI bootstrap",
		.offset	= 0,
		.size	= SZ_4K,
	}, {
		.name	= "Bootstrap config",
		.offset	= MTDPART_OFS_APPEND,
		.size	= SZ_4K,
	}, {
		.name	= "unallocated",
		.offset	= MTDPART_OFS_APPEND,
		.size	= MTDPART_SIZ_FULL,
	},
};

Without the sector erase this partition setup results in all of the
partitions being forced read-only.

Just my two cents...

Regards,
Hartley