// SPDX-License-Identifier: GPL-2.0-only
/*
 * A FSI master controller, using a simple GPIO bit-banging interface
 */

#include <linux/crc4.h>
#include <linux/delay.h>
#include <linux/device.h>
#include <linux/fsi.h>
#include <linux/gpio/consumer.h>
#include <linux/io.h>
#include <linux/irqflags.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/slab.h>

#include "fsi-master.h"

#define FSI_GPIO_STD_DLY        1       /* Standard pin delay in nS */
#define LAST_ADDR_INVALID               0x1

struct fsi_master_gpio {
        struct fsi_master       master;
        struct device           *dev;
        struct mutex            cmd_lock;       /* mutex for command ordering */
        struct gpio_desc        *gpio_clk;
        struct gpio_desc        *gpio_data;
        struct gpio_desc        *gpio_trans;    /* Voltage translator */
        struct gpio_desc        *gpio_enable;   /* FSI enable */
        struct gpio_desc        *gpio_mux;      /* Mux control */
        bool                    external_mode;
        bool                    no_delays;
        uint32_t                last_addr;
        uint8_t                 t_send_delay;
        uint8_t                 t_echo_delay;
};

#define CREATE_TRACE_POINTS
#include <trace/events/fsi_master_gpio.h>

#define to_fsi_master_gpio(m) container_of(m, struct fsi_master_gpio, master)

struct fsi_gpio_msg {
        uint64_t        msg;
        uint8_t         bits;
};

static void clock_toggle(struct fsi_master_gpio *master, int count)
{
        int i;

        for (i = 0; i < count; i++) {
                if (!master->no_delays)
                        ndelay(FSI_GPIO_STD_DLY);
                gpiod_set_value(master->gpio_clk, 0);
                if (!master->no_delays)
                        ndelay(FSI_GPIO_STD_DLY);
                gpiod_set_value(master->gpio_clk, 1);
        }
}

static int sda_clock_in(struct fsi_master_gpio *master)
{
        int in;

        if (!master->no_delays)
                ndelay(FSI_GPIO_STD_DLY);
        gpiod_set_value(master->gpio_clk, 0);

        /* Dummy read to feed the synchronizers */
        gpiod_get_value(master->gpio_data);

        /* Actual data read */
        in = gpiod_get_value(master->gpio_data);
        if (!master->no_delays)
                ndelay(FSI_GPIO_STD_DLY);
        gpiod_set_value(master->gpio_clk, 1);
        return in ? 1 : 0;
}

static void sda_out(struct fsi_master_gpio *master, int value)
{
        gpiod_set_value(master->gpio_data, value);
}

static void set_sda_input(struct fsi_master_gpio *master)
{
        gpiod_direction_input(master->gpio_data);
        gpiod_set_value(master->gpio_trans, 0);
}

static void set_sda_output(struct fsi_master_gpio *master, int value)
{
        gpiod_set_value(master->gpio_trans, 1);
        gpiod_direction_output(master->gpio_data, value);
}

static void clock_zeros(struct fsi_master_gpio *master, int count)
{
        trace_fsi_master_gpio_clock_zeros(master, count);
        set_sda_output(master, 1);
        clock_toggle(master, count);
}

static void echo_delay(struct fsi_master_gpio *master)
{
        clock_zeros(master, master->t_echo_delay);
}


static void serial_in(struct fsi_master_gpio *master, struct fsi_gpio_msg *msg,
                        uint8_t num_bits)
{
        uint8_t bit, in_bit;

        set_sda_input(master);

        for (bit = 0; bit < num_bits; bit++) {
                in_bit = sda_clock_in(master);
                msg->msg <<= 1;
                msg->msg |= ~in_bit & 0x1;      /* Data is active low */
        }
        msg->bits += num_bits;

        trace_fsi_master_gpio_in(master, num_bits, msg->msg);
}

static void serial_out(struct fsi_master_gpio *master,
                        const struct fsi_gpio_msg *cmd)
{
        uint8_t bit;
        uint64_t msg = ~cmd->msg;       /* Data is active low */
        uint64_t sda_mask = 0x1ULL << (cmd->bits - 1);
        uint64_t last_bit = ~0;
        int next_bit;

        trace_fsi_master_gpio_out(master, cmd->bits, cmd->msg);

        if (!cmd->bits) {
                dev_warn(master->dev, "trying to output 0 bits\n");
                return;
        }
        set_sda_output(master, 0);

        /* Send the start bit */
        sda_out(master, 0);
        clock_toggle(master, 1);

        /* Send the message */
        for (bit = 0; bit < cmd->bits; bit++) {
                next_bit = (msg & sda_mask) >> (cmd->bits - 1);
                if (last_bit ^ next_bit) {
                        sda_out(master, next_bit);
                        last_bit = next_bit;
                }
                clock_toggle(master, 1);
                msg <<= 1;
        }
}

static void msg_push_bits(struct fsi_gpio_msg *msg, uint64_t data, int bits)
{
        msg->msg <<= bits;
        msg->msg |= data & ((1ull << bits) - 1);
        msg->bits += bits;
}

static void msg_push_crc(struct fsi_gpio_msg *msg)
{
        uint8_t crc;
        int top;

        top = msg->bits & 0x3;

        /* start bit, and any non-aligned top bits */
        crc = crc4(0, 1 << top | msg->msg >> (msg->bits - top), top + 1);

        /* aligned bits */
        crc = crc4(crc, msg->msg, msg->bits - top);

        msg_push_bits(msg, crc, 4);
}

static bool check_same_address(struct fsi_master_gpio *master, int id,
                uint32_t addr)
{
        /* this will also handle LAST_ADDR_INVALID */
        return master->last_addr == (((id & 0x3) << 21) | (addr & ~0x3));
}

static bool check_relative_address(struct fsi_master_gpio *master, int id,
                uint32_t addr, uint32_t *rel_addrp)
{
        uint32_t last_addr = master->last_addr;
        int32_t rel_addr;

        if (last_addr == LAST_ADDR_INVALID)
                return false;

        /* We may be in 23-bit addressing mode, which uses the id as the
         * top two address bits. So, if we're referencing a different ID,
         * use absolute addresses.
         */
        if (((last_addr >> 21) & 0x3) != id)
                return false;

        /* remove the top two bits from any 23-bit addressing */
        last_addr &= (1 << 21) - 1;

        /* We know that the addresses are limited to 21 bits, so this won't
         * overflow the signed rel_addr */
        rel_addr = addr - last_addr;
        if (rel_addr > 255 || rel_addr < -256)
                return false;

        *rel_addrp = (uint32_t)rel_addr;

        return true;
}

static void last_address_update(struct fsi_master_gpio *master,
                int id, bool valid, uint32_t addr)
{
        if (!valid)
                master->last_addr = LAST_ADDR_INVALID;
        else
                master->last_addr = ((id & 0x3) << 21) | (addr & ~0x3);
}

/*
 * Encode an Absolute/Relative/Same Address command
 */
static void build_ar_command(struct fsi_master_gpio *master,
                struct fsi_gpio_msg *cmd, uint8_t id,
                uint32_t addr, size_t size, const void *data)
{
        int i, addr_bits, opcode_bits;
        bool write = !!data;
        uint8_t ds, opcode;
        uint32_t rel_addr;

        cmd->bits = 0;
        cmd->msg = 0;

        /* we have 21 bits of address max */
        addr &= ((1 << 21) - 1);

        /* cmd opcodes are variable length - SAME_AR is only two bits */
        opcode_bits = 3;

        if (check_same_address(master, id, addr)) {
                /* we still address the byte offset within the word */
                addr_bits = 2;
                opcode_bits = 2;
                opcode = FSI_CMD_SAME_AR;
                trace_fsi_master_gpio_cmd_same_addr(master);

        } else if (check_relative_address(master, id, addr, &rel_addr)) {
                /* 8 bits plus sign */
                addr_bits = 9;
                addr = rel_addr;
                opcode = FSI_CMD_REL_AR;
                trace_fsi_master_gpio_cmd_rel_addr(master, rel_addr);

        } else {
                addr_bits = 21;
                opcode = FSI_CMD_ABS_AR;
                trace_fsi_master_gpio_cmd_abs_addr(master, addr);
        }

        /*
         * The read/write size is encoded in the lower bits of the address
         * (as it must be naturally-aligned), and the following ds bit.
         *
         *      size    addr:1  addr:0  ds
         *      1       x       x       0
         *      2       x       0       1
         *      4       0       1       1
         *
         */
        ds = size > 1 ? 1 : 0;
        addr &= ~(size - 1);
        if (size == 4)
                addr |= 1;

        msg_push_bits(cmd, id, 2);
        msg_push_bits(cmd, opcode, opcode_bits);
        msg_push_bits(cmd, write ? 0 : 1, 1);
        msg_push_bits(cmd, addr, addr_bits);
        msg_push_bits(cmd, ds, 1);
        for (i = 0; write && i < size; i++)
                msg_push_bits(cmd, ((uint8_t *)data)[i], 8);

        msg_push_crc(cmd);
}

static void build_dpoll_command(struct fsi_gpio_msg *cmd, uint8_t slave_id)
{
        cmd->bits = 0;
        cmd->msg = 0;

        msg_push_bits(cmd, slave_id, 2);
        msg_push_bits(cmd, FSI_CMD_DPOLL, 3);
        msg_push_crc(cmd);
}

static void build_epoll_command(struct fsi_gpio_msg *cmd, uint8_t slave_id)
{
        cmd->bits = 0;
        cmd->msg = 0;

        msg_push_bits(cmd, slave_id, 2);
        msg_push_bits(cmd, FSI_CMD_EPOLL, 3);
        msg_push_crc(cmd);
}

static void build_term_command(struct fsi_gpio_msg *cmd, uint8_t slave_id)
{
        cmd->bits = 0;
        cmd->msg = 0;

        msg_push_bits(cmd, slave_id, 2);
        msg_push_bits(cmd, FSI_CMD_TERM, 6);
        msg_push_crc(cmd);
}

/*
 * Note: callers rely specifically on this returning -EAGAIN for
 * a CRC error detected in the response. Use other error code
 * for other situations. It will be converted to something else
 * higher up the stack before it reaches userspace.
 */
static int read_one_response(struct fsi_master_gpio *master,
                uint8_t data_size, struct fsi_gpio_msg *msgp, uint8_t *tagp)
{
        struct fsi_gpio_msg msg;
        unsigned long flags;
        uint32_t crc;
        uint8_t tag;
        int i;

        local_irq_save(flags);

        /* wait for the start bit */
        for (i = 0; i < FSI_MASTER_MTOE_COUNT; i++) {
                msg.bits = 0;
                msg.msg = 0;
                serial_in(master, &msg, 1);
                if (msg.msg)
                        break;
        }
        if (i == FSI_MASTER_MTOE_COUNT) {
                dev_dbg(master->dev,
                        "Master time out waiting for response\n");
                local_irq_restore(flags);
                return -ETIMEDOUT;
        }

        msg.bits = 0;
        msg.msg = 0;

        /* Read slave ID & response tag */
        serial_in(master, &msg, 4);

        tag = msg.msg & 0x3;

        /* If we have an ACK and we're expecting data, clock the data in too */
        if (tag == FSI_RESP_ACK && data_size)
                serial_in(master, &msg, data_size * 8);

        /* read CRC */
        serial_in(master, &msg, FSI_CRC_SIZE);

        local_irq_restore(flags);

        /* we have a whole message now; check CRC */
        crc = crc4(0, 1, 1);
        crc = crc4(crc, msg.msg, msg.bits);
        if (crc) {
                /* Check if it's all 1's, that probably means the host is off */
                if (((~msg.msg) & ((1ull << msg.bits) - 1)) == 0)
                        return -ENODEV;
                dev_dbg(master->dev, "ERR response CRC msg: 0x%016llx (%d bits)\n",
                        msg.msg, msg.bits);
                return -EAGAIN;
        }

        if (msgp)
                *msgp = msg;
        if (tagp)
                *tagp = tag;

        return 0;
}

static int issue_term(struct fsi_master_gpio *master, uint8_t slave)
{
        struct fsi_gpio_msg cmd;
        unsigned long flags;
        uint8_t tag;
        int rc;

        build_term_command(&cmd, slave);

        local_irq_save(flags);
        serial_out(master, &cmd);
        echo_delay(master);
        local_irq_restore(flags);

        rc = read_one_response(master, 0, NULL, &tag);
        if (rc < 0) {
                dev_err(master->dev,
                                "TERM failed; lost communication with slave\n");
                return -EIO;
        } else if (tag != FSI_RESP_ACK) {
                dev_err(master->dev, "TERM failed; response %d\n", tag);
                return -EIO;
        }

        return 0;
}

static int poll_for_response(struct fsi_master_gpio *master,
                uint8_t slave, uint8_t size, void *data)
{
        struct fsi_gpio_msg response, cmd;
        int busy_count = 0, rc, i;
        unsigned long flags;
        uint8_t tag;
        uint8_t *data_byte = data;
        int crc_err_retries = 0;
retry:
        rc = read_one_response(master, size, &response, &tag);

        /* Handle retries on CRC errors */
        if (rc == -EAGAIN) {
                /* Too many retries ? */
                if (crc_err_retries++ > FSI_CRC_ERR_RETRIES) {
                        /*
                         * Pass it up as a -EIO otherwise upper level will retry
                         * the whole command which isn't what we want here.
                         */
                        rc = -EIO;
                        goto fail;
                }
                dev_dbg(master->dev,
                         "CRC error retry %d\n", crc_err_retries);
                trace_fsi_master_gpio_crc_rsp_error(master);
                build_epoll_command(&cmd, slave);
                local_irq_save(flags);
                clock_zeros(master, FSI_MASTER_EPOLL_CLOCKS);
                serial_out(master, &cmd);
                echo_delay(master);
                local_irq_restore(flags);
                goto retry;
        } else if (rc)
                goto fail;

        switch (tag) {
        case FSI_RESP_ACK:
                if (size && data) {
                        uint64_t val = response.msg;
                        /* clear crc & mask */
                        val >>= 4;
                        val &= (1ull << (size * 8)) - 1;

                        for (i = 0; i < size; i++) {
                                data_byte[size-i-1] = val;
                                val >>= 8;
                        }
                }
                break;
        case FSI_RESP_BUSY:
                /*
                 * Its necessary to clock slave before issuing
                 * d-poll, not indicated in the hardware protocol
                 * spec. < 20 clocks causes slave to hang, 21 ok.
                 */
                if (busy_count++ < FSI_MASTER_MAX_BUSY) {
                        build_dpoll_command(&cmd, slave);
                        local_irq_save(flags);
                        clock_zeros(master, FSI_MASTER_DPOLL_CLOCKS);
                        serial_out(master, &cmd);
                        echo_delay(master);
                        local_irq_restore(flags);
                        goto retry;
                }
                dev_warn(master->dev,
                        "ERR slave is stuck in busy state, issuing TERM\n");
                local_irq_save(flags);
                clock_zeros(master, FSI_MASTER_DPOLL_CLOCKS);
                local_irq_restore(flags);
                issue_term(master, slave);
                rc = -EIO;
                break;

        case FSI_RESP_ERRA:
                dev_dbg(master->dev, "ERRA received: 0x%x\n", (int)response.msg);
                rc = -EIO;
                break;
        case FSI_RESP_ERRC:
                dev_dbg(master->dev, "ERRC received: 0x%x\n", (int)response.msg);
                trace_fsi_master_gpio_crc_cmd_error(master);
                rc = -EAGAIN;
                break;
        }

        if (busy_count > 0)
                trace_fsi_master_gpio_poll_response_busy(master, busy_count);
 fail:
        /*
         * tSendDelay clocks, avoids signal reflections when switching
         * from receive of response back to send of data.
         */
        local_irq_save(flags);
        clock_zeros(master, master->t_send_delay);
        local_irq_restore(flags);

        return rc;
}

static int send_request(struct fsi_master_gpio *master,
                struct fsi_gpio_msg *cmd)
{
        unsigned long flags;

        if (master->external_mode)
                return -EBUSY;

        local_irq_save(flags);
        serial_out(master, cmd);
        echo_delay(master);
        local_irq_restore(flags);

        return 0;
}

static int fsi_master_gpio_xfer(struct fsi_master_gpio *master, uint8_t slave,
                struct fsi_gpio_msg *cmd, size_t resp_len, void *resp)
{
        int rc = -EAGAIN, retries = 0;

        while ((retries++) < FSI_CRC_ERR_RETRIES) {
                rc = send_request(master, cmd);
                if (rc)
                        break;
                rc = poll_for_response(master, slave, resp_len, resp);
                if (rc != -EAGAIN)
                        break;
                rc = -EIO;
                dev_warn(master->dev, "ECRC retry %d\n", retries);

                /* Pace it a bit before retry */
                msleep(1);
        }

        return rc;
}

static int fsi_master_gpio_read(struct fsi_master *_master, int link,
                uint8_t id, uint32_t addr, void *val, size_t size)
{
        struct fsi_master_gpio *master = to_fsi_master_gpio(_master);
        struct fsi_gpio_msg cmd;
        int rc;

        if (link != 0)
                return -ENODEV;

        mutex_lock(&master->cmd_lock);
        build_ar_command(master, &cmd, id, addr, size, NULL);
        rc = fsi_master_gpio_xfer(master, id, &cmd, size, val);
        last_address_update(master, id, rc == 0, addr);
        mutex_unlock(&master->cmd_lock);

        return rc;
}

static int fsi_master_gpio_write(struct fsi_master *_master, int link,
                uint8_t id, uint32_t addr, const void *val, size_t size)
{
        struct fsi_master_gpio *master = to_fsi_master_gpio(_master);
        struct fsi_gpio_msg cmd;
        int rc;

        if (link != 0)
                return -ENODEV;

        mutex_lock(&master->cmd_lock);
        build_ar_command(master, &cmd, id, addr, size, val);
        rc = fsi_master_gpio_xfer(master, id, &cmd, 0, NULL);
        last_address_update(master, id, rc == 0, addr);
        mutex_unlock(&master->cmd_lock);

        return rc;
}

static int fsi_master_gpio_term(struct fsi_master *_master,
                int link, uint8_t id)
{
        struct fsi_master_gpio *master = to_fsi_master_gpio(_master);
        struct fsi_gpio_msg cmd;
        int rc;

        if (link != 0)
                return -ENODEV;

        mutex_lock(&master->cmd_lock);
        build_term_command(&cmd, id);
        rc = fsi_master_gpio_xfer(master, id, &cmd, 0, NULL);
        last_address_update(master, id, false, 0);
        mutex_unlock(&master->cmd_lock);

        return rc;
}

static int fsi_master_gpio_break(struct fsi_master *_master, int link)
{
        struct fsi_master_gpio *master = to_fsi_master_gpio(_master);
        unsigned long flags;

        if (link != 0)
                return -ENODEV;

        trace_fsi_master_gpio_break(master);

        mutex_lock(&master->cmd_lock);
        if (master->external_mode) {
                mutex_unlock(&master->cmd_lock);
                return -EBUSY;
        }

        local_irq_save(flags);

        set_sda_output(master, 1);
        sda_out(master, 1);
        clock_toggle(master, FSI_PRE_BREAK_CLOCKS);
        sda_out(master, 0);
        clock_toggle(master, FSI_BREAK_CLOCKS);
        echo_delay(master);
        sda_out(master, 1);
        clock_toggle(master, FSI_POST_BREAK_CLOCKS);

        local_irq_restore(flags);

        last_address_update(master, 0, false, 0);
        mutex_unlock(&master->cmd_lock);

        /* Wait for logic reset to take effect */
        udelay(200);

        return 0;
}

static void fsi_master_gpio_init(struct fsi_master_gpio *master)
{
        unsigned long flags;

        gpiod_direction_output(master->gpio_mux, 1);
        gpiod_direction_output(master->gpio_trans, 1);
        gpiod_direction_output(master->gpio_enable, 1);
        gpiod_direction_output(master->gpio_clk, 1);
        gpiod_direction_output(master->gpio_data, 1);

        /* todo: evaluate if clocks can be reduced */
        local_irq_save(flags);
        clock_zeros(master, FSI_INIT_CLOCKS);
        local_irq_restore(flags);
}

static void fsi_master_gpio_init_external(struct fsi_master_gpio *master)
{
        gpiod_direction_output(master->gpio_mux, 0);
        gpiod_direction_output(master->gpio_trans, 0);
        gpiod_direction_output(master->gpio_enable, 1);
        gpiod_direction_input(master->gpio_clk);
        gpiod_direction_input(master->gpio_data);
}

static int fsi_master_gpio_link_enable(struct fsi_master *_master, int link)
{
        struct fsi_master_gpio *master = to_fsi_master_gpio(_master);
        int rc = -EBUSY;

        if (link != 0)
                return -ENODEV;

        mutex_lock(&master->cmd_lock);
        if (!master->external_mode) {
                gpiod_set_value(master->gpio_enable, 1);
                rc = 0;
        }
        mutex_unlock(&master->cmd_lock);

        return rc;
}

static int fsi_master_gpio_link_config(struct fsi_master *_master, int link,
                                       u8 t_send_delay, u8 t_echo_delay)
{
        struct fsi_master_gpio *master = to_fsi_master_gpio(_master);

        if (link != 0)
                return -ENODEV;

        mutex_lock(&master->cmd_lock);
        master->t_send_delay = t_send_delay;
        master->t_echo_delay = t_echo_delay;
        mutex_unlock(&master->cmd_lock);

        return 0;
}

static ssize_t external_mode_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct fsi_master_gpio *master = dev_get_drvdata(dev);

        return snprintf(buf, PAGE_SIZE - 1, "%u\n",
                        master->external_mode ? 1 : 0);
}

static ssize_t external_mode_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t count)
{
        struct fsi_master_gpio *master = dev_get_drvdata(dev);
        unsigned long val;
        bool external_mode;
        int err;

        err = kstrtoul(buf, 0, &val);
        if (err)
                return err;

        external_mode = !!val;

        mutex_lock(&master->cmd_lock);

        if (external_mode == master->external_mode) {
                mutex_unlock(&master->cmd_lock);
                return count;
        }

        master->external_mode = external_mode;
        if (master->external_mode)
                fsi_master_gpio_init_external(master);
        else
                fsi_master_gpio_init(master);

        mutex_unlock(&master->cmd_lock);

        fsi_master_rescan(&master->master);

        return count;
}

static DEVICE_ATTR(external_mode, 0664,
                external_mode_show, external_mode_store);

static void fsi_master_gpio_release(struct device *dev)
{
        struct fsi_master_gpio *master = to_fsi_master_gpio(dev_to_fsi_master(dev));

        of_node_put(dev_of_node(master->dev));

        kfree(master);
}

static int fsi_master_gpio_probe(struct platform_device *pdev)
{
        struct fsi_master_gpio *master;
        struct gpio_desc *gpio;
        int rc;

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

        master->dev = &pdev->dev;
        master->master.dev.parent = master->dev;
        master->master.dev.of_node = of_node_get(dev_of_node(master->dev));
        master->master.dev.release = fsi_master_gpio_release;
        master->last_addr = LAST_ADDR_INVALID;

        gpio = devm_gpiod_get(&pdev->dev, "clock", 0);
        if (IS_ERR(gpio)) {
                dev_err(&pdev->dev, "failed to get clock gpio\n");
                rc = PTR_ERR(gpio);
                goto err_free;
        }
        master->gpio_clk = gpio;

        gpio = devm_gpiod_get(&pdev->dev, "data", 0);
        if (IS_ERR(gpio)) {
                dev_err(&pdev->dev, "failed to get data gpio\n");
                rc = PTR_ERR(gpio);
                goto err_free;
        }
        master->gpio_data = gpio;

        /* Optional GPIOs */
        gpio = devm_gpiod_get_optional(&pdev->dev, "trans", 0);
        if (IS_ERR(gpio)) {
                dev_err(&pdev->dev, "failed to get trans gpio\n");
                rc = PTR_ERR(gpio);
                goto err_free;
        }
        master->gpio_trans = gpio;

        gpio = devm_gpiod_get_optional(&pdev->dev, "enable", 0);
        if (IS_ERR(gpio)) {
                dev_err(&pdev->dev, "failed to get enable gpio\n");
                rc = PTR_ERR(gpio);
                goto err_free;
        }
        master->gpio_enable = gpio;

        gpio = devm_gpiod_get_optional(&pdev->dev, "mux", 0);
        if (IS_ERR(gpio)) {
                dev_err(&pdev->dev, "failed to get mux gpio\n");
                rc = PTR_ERR(gpio);
                goto err_free;
        }
        master->gpio_mux = gpio;

        /*
         * Check if GPIO block is slow enought that no extra delays
         * are necessary. This improves performance on ast2500 by
         * an order of magnitude.
         */
        master->no_delays = device_property_present(&pdev->dev, "no-gpio-delays");

        /* Default FSI command delays */
        master->t_send_delay = FSI_SEND_DELAY_CLOCKS;
        master->t_echo_delay = FSI_ECHO_DELAY_CLOCKS;

        master->master.n_links = 1;
        master->master.flags = FSI_MASTER_FLAG_SWCLOCK;
        master->master.read = fsi_master_gpio_read;
        master->master.write = fsi_master_gpio_write;
        master->master.term = fsi_master_gpio_term;
        master->master.send_break = fsi_master_gpio_break;
        master->master.link_enable = fsi_master_gpio_link_enable;
        master->master.link_config = fsi_master_gpio_link_config;
        platform_set_drvdata(pdev, master);
        mutex_init(&master->cmd_lock);

        fsi_master_gpio_init(master);

        rc = device_create_file(&pdev->dev, &dev_attr_external_mode);
        if (rc)
                goto err_free;

        rc = fsi_master_register(&master->master);
        if (rc) {
                device_remove_file(&pdev->dev, &dev_attr_external_mode);
                put_device(&master->master.dev);
                return rc;
        }
        return 0;
 err_free:
        kfree(master);
        return rc;
}



static int fsi_master_gpio_remove(struct platform_device *pdev)
{
        struct fsi_master_gpio *master = platform_get_drvdata(pdev);

        device_remove_file(&pdev->dev, &dev_attr_external_mode);

        fsi_master_unregister(&master->master);

        return 0;
}

static const struct of_device_id fsi_master_gpio_match[] = {
        { .compatible = "fsi-master-gpio" },
        { },
};

static struct platform_driver fsi_master_gpio_driver = {
        .driver = {
                .name           = "fsi-master-gpio",
                .of_match_table = fsi_master_gpio_match,
        },
        .probe  = fsi_master_gpio_probe,
        .remove = fsi_master_gpio_remove,
};

module_platform_driver(fsi_master_gpio_driver);
MODULE_LICENSE("GPL");