// 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
  ");
  		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
  ");

  		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)
  ",
  			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
  ");
  		return -EIO;

  	} else if (tag != FSI_RESP_ACK) {

  		dev_err(master->dev, "TERM failed; response %d
  ", 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
  ", 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
  ");

  		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
  ", (int)response.msg);

  		rc = -EIO;
  		break;

  	case FSI_RESP_ERRC:

  		dev_dbg(master->dev, "ERRC received: 0x%x
  ", (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
  ", 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
  ",
  			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
  ");

  		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
  ");

  		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
  ");

  		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
  ");

  		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
  ");

  		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");