/*
 * at25.c -- support most SPI EEPROMs, such as Atmel AT25 models
 *
 * Copyright (C) 2006 David Brownell
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 */

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/device.h>
#include <linux/sched.h>

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


/*
 * NOTE: this is an *EEPROM* driver.  The vagaries of product naming
 * mean that some AT25 products are EEPROMs, and others are FLASH.
 * Handle FLASH chips with the drivers/mtd/devices/m25p80.c driver,
 * not this one!
 */

struct at25_data {
        struct spi_device       *spi;
        struct memory_accessor  mem;
        struct mutex            lock;
        struct spi_eeprom       chip;
        struct bin_attribute    bin;
        unsigned                addrlen;
};

#define AT25_WREN       0x06            /* latch the write enable */
#define AT25_WRDI       0x04            /* reset the write enable */
#define AT25_RDSR       0x05            /* read status register */
#define AT25_WRSR       0x01            /* write status register */
#define AT25_READ       0x03            /* read byte(s) */
#define AT25_WRITE      0x02            /* write byte(s)/sector */

#define AT25_SR_nRDY    0x01            /* nRDY = write-in-progress */
#define AT25_SR_WEN     0x02            /* write enable (latched) */
#define AT25_SR_BP0     0x04            /* BP for software writeprotect */
#define AT25_SR_BP1     0x08
#define AT25_SR_WPEN    0x80            /* writeprotect enable */


#define EE_MAXADDRLEN   3               /* 24 bit addresses, up to 2 MBytes */

/* Specs often allow 5 msec for a page write, sometimes 20 msec;
 * it's important to recover from write timeouts.
 */
#define EE_TIMEOUT      25

/*-------------------------------------------------------------------------*/

#define io_limit        PAGE_SIZE       /* bytes */

static ssize_t
at25_ee_read(
        struct at25_data        *at25,
        char                    *buf,
        unsigned                offset,
        size_t                  count
)
{
        u8                      command[EE_MAXADDRLEN + 1];
        u8                      *cp;
        ssize_t                 status;
        struct spi_transfer     t[2];
        struct spi_message      m;

        if (unlikely(offset >= at25->bin.size))
                return 0;
        if ((offset + count) > at25->bin.size)
                count = at25->bin.size - offset;
        if (unlikely(!count))
                return count;

        cp = command;
        *cp++ = AT25_READ;

        /* 8/16/24-bit address is written MSB first */
        switch (at25->addrlen) {
        default:        /* case 3 */
                *cp++ = offset >> 16;
        case 2:
                *cp++ = offset >> 8;
        case 1:
        case 0: /* can't happen: for better codegen */
                *cp++ = offset >> 0;
        }

        spi_message_init(&m);
        memset(t, 0, sizeof t);

        t[0].tx_buf = command;
        t[0].len = at25->addrlen + 1;
        spi_message_add_tail(&t[0], &m);

        t[1].rx_buf = buf;
        t[1].len = count;
        spi_message_add_tail(&t[1], &m);

        mutex_lock(&at25->lock);

        /* Read it all at once.
         *
         * REVISIT that's potentially a problem with large chips, if
         * other devices on the bus need to be accessed regularly or
         * this chip is clocked very slowly
         */
        status = spi_sync(at25->spi, &m);
        dev_dbg(&at25->spi->dev,
                "read %Zd bytes at %d --> %d\n",
                count, offset, (int) status);

        mutex_unlock(&at25->lock);
        return status ? status : count;
}

static ssize_t
at25_bin_read(struct file *filp, struct kobject *kobj,
              struct bin_attribute *bin_attr,
              char *buf, loff_t off, size_t count)
{
        struct device           *dev;
        struct at25_data        *at25;

        dev = container_of(kobj, struct device, kobj);
        at25 = dev_get_drvdata(dev);

        return at25_ee_read(at25, buf, off, count);
}


static ssize_t
at25_ee_write(struct at25_data *at25, const char *buf, loff_t off,
              size_t count)
{
        ssize_t                 status = 0;
        unsigned                written = 0;
        unsigned                buf_size;
        u8                      *bounce;

        if (unlikely(off >= at25->bin.size))
                return -EFBIG;
        if ((off + count) > at25->bin.size)
                count = at25->bin.size - off;
        if (unlikely(!count))
                return count;

        /* Temp buffer starts with command and address */
        buf_size = at25->chip.page_size;
        if (buf_size > io_limit)
                buf_size = io_limit;
        bounce = kmalloc(buf_size + at25->addrlen + 1, GFP_KERNEL);
        if (!bounce)
                return -ENOMEM;

        /* For write, rollover is within the page ... so we write at
         * most one page, then manually roll over to the next page.
         */
        bounce[0] = AT25_WRITE;
        mutex_lock(&at25->lock);
        do {
                unsigned long   timeout, retries;
                unsigned        segment;
                unsigned        offset = (unsigned) off;
                u8              *cp = bounce + 1;
                int             sr;

                *cp = AT25_WREN;
                status = spi_write(at25->spi, cp, 1);
                if (status < 0) {
                        dev_dbg(&at25->spi->dev, "WREN --> %d\n",
                                        (int) status);
                        break;
                }

                /* 8/16/24-bit address is written MSB first */
                switch (at25->addrlen) {
                default:        /* case 3 */
                        *cp++ = offset >> 16;
                case 2:
                        *cp++ = offset >> 8;
                case 1:
                case 0: /* can't happen: for better codegen */
                        *cp++ = offset >> 0;
                }

                /* Write as much of a page as we can */
                segment = buf_size - (offset % buf_size);
                if (segment > count)
                        segment = count;
                memcpy(cp, buf, segment);
                status = spi_write(at25->spi, bounce,
                                segment + at25->addrlen + 1);
                dev_dbg(&at25->spi->dev,
                                "write %u bytes at %u --> %d\n",
                                segment, offset, (int) status);
                if (status < 0)
                        break;

                /* REVISIT this should detect (or prevent) failed writes
                 * to readonly sections of the EEPROM...
                 */

                /* Wait for non-busy status */
                timeout = jiffies + msecs_to_jiffies(EE_TIMEOUT);
                retries = 0;
                do {

                        sr = spi_w8r8(at25->spi, AT25_RDSR);
                        if (sr < 0 || (sr & AT25_SR_nRDY)) {
                                dev_dbg(&at25->spi->dev,
                                        "rdsr --> %d (%02x)\n", sr, sr);
                                /* at HZ=100, this is sloooow */
                                msleep(1);
                                continue;
                        }
                        if (!(sr & AT25_SR_nRDY))
                                break;
                } while (retries++ < 3 || time_before_eq(jiffies, timeout));

                if ((sr < 0) || (sr & AT25_SR_nRDY)) {
                        dev_err(&at25->spi->dev,
                                "write %d bytes offset %d, "
                                "timeout after %u msecs\n",
                                segment, offset,
                                jiffies_to_msecs(jiffies -
                                        (timeout - EE_TIMEOUT)));
                        status = -ETIMEDOUT;
                        break;
                }

                off += segment;
                buf += segment;
                count -= segment;
                written += segment;

        } while (count > 0);

        mutex_unlock(&at25->lock);

        kfree(bounce);
        return written ? written : status;
}

static ssize_t
at25_bin_write(struct file *filp, struct kobject *kobj,
               struct bin_attribute *bin_attr,
               char *buf, loff_t off, size_t count)
{
        struct device           *dev;
        struct at25_data        *at25;

        dev = container_of(kobj, struct device, kobj);
        at25 = dev_get_drvdata(dev);

        return at25_ee_write(at25, buf, off, count);
}

/*-------------------------------------------------------------------------*/

/* Let in-kernel code access the eeprom data. */

static ssize_t at25_mem_read(struct memory_accessor *mem, char *buf,
                         off_t offset, size_t count)
{
        struct at25_data *at25 = container_of(mem, struct at25_data, mem);

        return at25_ee_read(at25, buf, offset, count);
}

static ssize_t at25_mem_write(struct memory_accessor *mem, const char *buf,
                          off_t offset, size_t count)
{
        struct at25_data *at25 = container_of(mem, struct at25_data, mem);

        return at25_ee_write(at25, buf, offset, count);
}

/*-------------------------------------------------------------------------*/

static int at25_probe(struct spi_device *spi)
{
        struct at25_data        *at25 = NULL;
        const struct spi_eeprom *chip;
        int                     err;
        int                     sr;
        int                     addrlen;

        /* Chip description */
        chip = spi->dev.platform_data;
        if (!chip) {
                dev_dbg(&spi->dev, "no chip description\n");
                err = -ENODEV;
                goto fail;
        }

        /* For now we only support 8/16/24 bit addressing */
        if (chip->flags & EE_ADDR1)
                addrlen = 1;
        else if (chip->flags & EE_ADDR2)
                addrlen = 2;
        else if (chip->flags & EE_ADDR3)
                addrlen = 3;
        else {
                dev_dbg(&spi->dev, "unsupported address type\n");
                err = -EINVAL;
                goto fail;
        }

        /* Ping the chip ... the status register is pretty portable,
         * unlike probing manufacturer IDs.  We do expect that system
         * firmware didn't write it in the past few milliseconds!
         */
        sr = spi_w8r8(spi, AT25_RDSR);
        if (sr < 0 || sr & AT25_SR_nRDY) {
                dev_dbg(&spi->dev, "rdsr --> %d (%02x)\n", sr, sr);
                err = -ENXIO;
                goto fail;
        }

        if (!(at25 = kzalloc(sizeof *at25, GFP_KERNEL))) {
                err = -ENOMEM;
                goto fail;
        }

        mutex_init(&at25->lock);
        at25->chip = *chip;
        at25->spi = spi_dev_get(spi);
        dev_set_drvdata(&spi->dev, at25);
        at25->addrlen = addrlen;

        /* Export the EEPROM bytes through sysfs, since that's convenient.
         * And maybe to other kernel code; it might hold a board's Ethernet
         * address, or board-specific calibration data generated on the
         * manufacturing floor.
         *
         * Default to root-only access to the data; EEPROMs often hold data
         * that's sensitive for read and/or write, like ethernet addresses,
         * security codes, board-specific manufacturing calibrations, etc.
         */
        sysfs_bin_attr_init(&at25->bin);
        at25->bin.attr.name = "eeprom";
        at25->bin.attr.mode = S_IRUSR;
        at25->bin.read = at25_bin_read;
        at25->mem.read = at25_mem_read;

        at25->bin.size = at25->chip.byte_len;
        if (!(chip->flags & EE_READONLY)) {
                at25->bin.write = at25_bin_write;
                at25->bin.attr.mode |= S_IWUSR;
                at25->mem.write = at25_mem_write;
        }

        err = sysfs_create_bin_file(&spi->dev.kobj, &at25->bin);
        if (err)
                goto fail;

        if (chip->setup)
                chip->setup(&at25->mem, chip->context);

        dev_info(&spi->dev, "%Zd %s %s eeprom%s, pagesize %u\n",
                (at25->bin.size < 1024)
                        ? at25->bin.size
                        : (at25->bin.size / 1024),
                (at25->bin.size < 1024) ? "Byte" : "KByte",
                at25->chip.name,
                (chip->flags & EE_READONLY) ? " (readonly)" : "",
                at25->chip.page_size);
        return 0;
fail:
        dev_dbg(&spi->dev, "probe err %d\n", err);
        kfree(at25);
        return err;
}

static int __devexit at25_remove(struct spi_device *spi)
{
        struct at25_data        *at25;

        at25 = dev_get_drvdata(&spi->dev);
        sysfs_remove_bin_file(&spi->dev.kobj, &at25->bin);
        kfree(at25);
        return 0;
}

/*-------------------------------------------------------------------------*/

static struct spi_driver at25_driver = {
        .driver = {
                .name           = "at25",
                .owner          = THIS_MODULE,
        },
        .probe          = at25_probe,
        .remove         = __devexit_p(at25_remove),
};

static int __init at25_init(void)
{
        return spi_register_driver(&at25_driver);
}
module_init(at25_init);

static void __exit at25_exit(void)
{
        spi_unregister_driver(&at25_driver);
}
module_exit(at25_exit);

MODULE_DESCRIPTION("Driver for most SPI EEPROMs");
MODULE_AUTHOR("David Brownell");
MODULE_LICENSE("GPL");
MODULE_ALIAS("spi:at25");