drivers/input/serio/ps2-gpio.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * GPIO based serio bus driver for bit banging the PS/2 protocol
  *
  * Author: Danilo Krummrich <danilokrummrich@dk-develop.de>
  */

 #include <linux/gpio/consumer.h>
 #include <linux/interrupt.h>
 #include <linux/module.h>
 #include <linux/serio.h>
 #include <linux/slab.h>
 #include <linux/platform_device.h>
 #include <linux/workqueue.h>
 #include <linux/completion.h>
 #include <linux/mutex.h>
 #include <linux/preempt.h>
 #include <linux/property.h>
 #include <linux/of.h>
 #include <linux/jiffies.h>
 #include <linux/delay.h>
 #include <linux/timekeeping.h>

 #define DRIVER_NAME		"ps2-gpio"

 #define PS2_MODE_RX		0
 #define PS2_MODE_TX		1

 #define PS2_START_BIT		0
 #define PS2_DATA_BIT0		1
 #define PS2_DATA_BIT1		2
 #define PS2_DATA_BIT2		3
 #define PS2_DATA_BIT3		4
 #define PS2_DATA_BIT4		5
 #define PS2_DATA_BIT5		6
 #define PS2_DATA_BIT6		7
 #define PS2_DATA_BIT7		8
 #define PS2_PARITY_BIT		9
 #define PS2_STOP_BIT		10
 #define PS2_ACK_BIT		11

 #define PS2_DEV_RET_ACK		0xfa
 #define PS2_DEV_RET_NACK	0xfe

 #define PS2_CMD_RESEND		0xfe

 /*
  * The PS2 protocol specifies a clock frequency between 10kHz and 16.7kHz,
  * therefore the maximal interrupt interval should be 100us and the minimum
  * interrupt interval should be ~60us. Let's allow +/- 20us for frequency
  * deviations and interrupt latency.
  *
  * The data line must be samples after ~30us to 50us after the falling edge,
  * since the device updates the data line at the rising edge.
  *
  * ___            ______            ______            ______            ___
  *    \          /      \          /      \          /      \          /
  *     \        /        \        /        \        /        \        /
  *      \______/          \______/          \______/          \______/
  *
  *     |-----------------|                 |--------|
  *          60us/100us                      30us/50us
  */
 #define PS2_CLK_FREQ_MIN_HZ		10000
 #define PS2_CLK_FREQ_MAX_HZ		16700
 #define PS2_CLK_MIN_INTERVAL_US		((1000 * 1000) / PS2_CLK_FREQ_MAX_HZ)
 #define PS2_CLK_MAX_INTERVAL_US		((1000 * 1000) / PS2_CLK_FREQ_MIN_HZ)
 #define PS2_IRQ_MIN_INTERVAL_US		(PS2_CLK_MIN_INTERVAL_US - 20)
 #define PS2_IRQ_MAX_INTERVAL_US		(PS2_CLK_MAX_INTERVAL_US + 20)

 struct ps2_gpio_data {
 	struct device *dev;
 	struct serio *serio;
 	unsigned char mode;
 	struct gpio_desc *gpio_clk;
 	struct gpio_desc *gpio_data;
 	bool write_enable;
 	int irq;
 	ktime_t t_irq_now;
 	ktime_t t_irq_last;
 	struct {
 		unsigned char cnt;
 		unsigned char byte;
 	} rx;
 	struct {
 		unsigned char cnt;
 		unsigned char byte;
 		ktime_t t_xfer_start;
 		ktime_t t_xfer_end;
 		struct completion complete;
 		struct mutex mutex;
 		struct delayed_work work;
 	} tx;
 };

 static int ps2_gpio_open(struct serio *serio)
 {
 	struct ps2_gpio_data *drvdata = serio->port_data;

 	drvdata->t_irq_last = 0;
 	drvdata->tx.t_xfer_end = 0;

 	enable_irq(drvdata->irq);
 	return 0;
 }

 static void ps2_gpio_close(struct serio *serio)
 {
 	struct ps2_gpio_data *drvdata = serio->port_data;

 	flush_delayed_work(&drvdata->tx.work);
 	disable_irq(drvdata->irq);
 }

 static int __ps2_gpio_write(struct serio *serio, unsigned char val)
 {
 	struct ps2_gpio_data *drvdata = serio->port_data;

 	disable_irq_nosync(drvdata->irq);
 	gpiod_direction_output(drvdata->gpio_clk, 0);

 	drvdata->mode = PS2_MODE_TX;
 	drvdata->tx.byte = val;

 	schedule_delayed_work(&drvdata->tx.work, usecs_to_jiffies(200));

 	return 0;
 }

 static int ps2_gpio_write(struct serio *serio, unsigned char val)
 {
 	struct ps2_gpio_data *drvdata = serio->port_data;
 	int ret = 0;

 	if (in_task()) {
 		mutex_lock(&drvdata->tx.mutex);
 		__ps2_gpio_write(serio, val);
 		if (!wait_for_completion_timeout(&drvdata->tx.complete,
 						 msecs_to_jiffies(10000)))
 			ret = SERIO_TIMEOUT;
 		mutex_unlock(&drvdata->tx.mutex);
 	} else {
 		__ps2_gpio_write(serio, val);
 	}

 	return ret;
 }

 static void ps2_gpio_tx_work_fn(struct work_struct *work)
 {
 	struct delayed_work *dwork = to_delayed_work(work);
 	struct ps2_gpio_data *drvdata = container_of(dwork,
 						     struct ps2_gpio_data,
 						     tx.work);

 	drvdata->tx.t_xfer_start = ktime_get();
 	enable_irq(drvdata->irq);
 	gpiod_direction_output(drvdata->gpio_data, 0);
 	gpiod_direction_input(drvdata->gpio_clk);
 }

 static irqreturn_t ps2_gpio_irq_rx(struct ps2_gpio_data *drvdata)
 {
 	unsigned char byte, cnt;
 	int data;
 	int rxflags = 0;
 	s64 us_delta;

 	byte = drvdata->rx.byte;
 	cnt = drvdata->rx.cnt;

 	drvdata->t_irq_now = ktime_get();

 	/*
 	 * We need to consider spurious interrupts happening right after
 	 * a TX xfer finished.
 	 */
 	us_delta = ktime_us_delta(drvdata->t_irq_now, drvdata->tx.t_xfer_end);
 	if (unlikely(us_delta < PS2_IRQ_MIN_INTERVAL_US))
 		goto end;

 	us_delta = ktime_us_delta(drvdata->t_irq_now, drvdata->t_irq_last);
 	if (us_delta > PS2_IRQ_MAX_INTERVAL_US && cnt) {
 		dev_err(drvdata->dev,
 			"RX: timeout, probably we missed an interrupt\n");
 		goto err;
 	} else if (unlikely(us_delta < PS2_IRQ_MIN_INTERVAL_US)) {
 		/* Ignore spurious IRQs. */
 		goto end;
 	}
 	drvdata->t_irq_last = drvdata->t_irq_now;

 	data = gpiod_get_value(drvdata->gpio_data);
 	if (unlikely(data < 0)) {
 		dev_err(drvdata->dev, "RX: failed to get data gpio val: %d\n",
 			data);
 		goto err;
 	}

 	switch (cnt) {
 	case PS2_START_BIT:
 		/* start bit should be low */
 		if (unlikely(data)) {
 			dev_err(drvdata->dev, "RX: start bit should be low\n");
 			goto err;
 		}
 		break;
 	case PS2_DATA_BIT0:
 	case PS2_DATA_BIT1:
 	case PS2_DATA_BIT2:
 	case PS2_DATA_BIT3:
 	case PS2_DATA_BIT4:
 	case PS2_DATA_BIT5:
 	case PS2_DATA_BIT6:
 	case PS2_DATA_BIT7:
 		/* processing data bits */
 		if (data)
 			byte |= (data << (cnt - 1));
 		break;
 	case PS2_PARITY_BIT:
 		/* check odd parity */
 		if (!((hweight8(byte) & 1) ^ data)) {
 			rxflags |= SERIO_PARITY;
 			dev_warn(drvdata->dev, "RX: parity error\n");
 			if (!drvdata->write_enable)
 				goto err;
 		}
 		break;
 	case PS2_STOP_BIT:
 		/* stop bit should be high */
 		if (unlikely(!data)) {
 			dev_err(drvdata->dev, "RX: stop bit should be high\n");
 			goto err;
 		}

 		/*
 		 * Do not send spurious ACK's and NACK's when write fn is
 		 * not provided.
 		 */
 		if (!drvdata->write_enable) {
 			if (byte == PS2_DEV_RET_NACK)
 				goto err;
 			else if (byte == PS2_DEV_RET_ACK)
 				break;
 		}

 		serio_interrupt(drvdata->serio, byte, rxflags);
 		dev_dbg(drvdata->dev, "RX: sending byte 0x%x\n", byte);

 		cnt = byte = 0;

 		goto end; /* success */
 	default:
 		dev_err(drvdata->dev, "RX: got out of sync with the device\n");
 		goto err;
 	}

 	cnt++;
 	goto end; /* success */

 err:
 	cnt = byte = 0;
 	__ps2_gpio_write(drvdata->serio, PS2_CMD_RESEND);
 end:
 	drvdata->rx.cnt = cnt;
 	drvdata->rx.byte = byte;
 	return IRQ_HANDLED;
 }

 static irqreturn_t ps2_gpio_irq_tx(struct ps2_gpio_data *drvdata)
 {
 	unsigned char byte, cnt;
 	int data;
 	s64 us_delta;

 	cnt = drvdata->tx.cnt;
 	byte = drvdata->tx.byte;

 	drvdata->t_irq_now = ktime_get();

 	/*
 	 * There might be pending IRQs since we disabled IRQs in
 	 * __ps2_gpio_write().  We can expect at least one clock period until
 	 * the device generates the first falling edge after releasing the
 	 * clock line.
 	 */
 	us_delta = ktime_us_delta(drvdata->t_irq_now,
 				  drvdata->tx.t_xfer_start);
 	if (unlikely(us_delta < PS2_CLK_MIN_INTERVAL_US))
 		goto end;

 	us_delta = ktime_us_delta(drvdata->t_irq_now, drvdata->t_irq_last);
 	if (us_delta > PS2_IRQ_MAX_INTERVAL_US && cnt > 1) {
 		dev_err(drvdata->dev,
 			"TX: timeout, probably we missed an interrupt\n");
 		goto err;
 	} else if (unlikely(us_delta < PS2_IRQ_MIN_INTERVAL_US)) {
 		/* Ignore spurious IRQs. */
 		goto end;
 	}
 	drvdata->t_irq_last = drvdata->t_irq_now;

 	switch (cnt) {
 	case PS2_START_BIT:
 		/* should never happen */
 		dev_err(drvdata->dev,
 			"TX: start bit should have been sent already\n");
 		goto err;
 	case PS2_DATA_BIT0:
 	case PS2_DATA_BIT1:
 	case PS2_DATA_BIT2:
 	case PS2_DATA_BIT3:
 	case PS2_DATA_BIT4:
 	case PS2_DATA_BIT5:
 	case PS2_DATA_BIT6:
 	case PS2_DATA_BIT7:
 		data = byte & BIT(cnt - 1);
 		gpiod_set_value(drvdata->gpio_data, data);
 		break;
 	case PS2_PARITY_BIT:
 		/* do odd parity */
 		data = !(hweight8(byte) & 1);
 		gpiod_set_value(drvdata->gpio_data, data);
 		break;
 	case PS2_STOP_BIT:
 		/* release data line to generate stop bit */
 		gpiod_direction_input(drvdata->gpio_data);
 		break;
 	case PS2_ACK_BIT:
 		data = gpiod_get_value(drvdata->gpio_data);
 		if (data) {
 			dev_warn(drvdata->dev, "TX: received NACK, retry\n");
 			goto err;
 		}

 		drvdata->tx.t_xfer_end = ktime_get();
 		drvdata->mode = PS2_MODE_RX;
 		complete(&drvdata->tx.complete);

 		cnt = 1;
 		goto end; /* success */
 	default:
 		/*
 		 * Probably we missed the stop bit. Therefore we release data
 		 * line and try again.
 		 */
 		gpiod_direction_input(drvdata->gpio_data);
 		dev_err(drvdata->dev, "TX: got out of sync with the device\n");
 		goto err;
 	}

 	cnt++;
 	goto end; /* success */

 err:
 	cnt = 1;
 	gpiod_direction_input(drvdata->gpio_data);
 	__ps2_gpio_write(drvdata->serio, drvdata->tx.byte);
 end:
 	drvdata->tx.cnt = cnt;
 	return IRQ_HANDLED;
 }

 static irqreturn_t ps2_gpio_irq(int irq, void *dev_id)
 {
 	struct ps2_gpio_data *drvdata = dev_id;

 	return drvdata->mode ? ps2_gpio_irq_tx(drvdata) :
 		ps2_gpio_irq_rx(drvdata);
 }

 static int ps2_gpio_get_props(struct device *dev,
 				 struct ps2_gpio_data *drvdata)
 {
 	enum gpiod_flags gflags;

 	/* Enforce open drain, since this is required by the PS/2 bus. */
 	gflags = GPIOD_IN | GPIOD_FLAGS_BIT_OPEN_DRAIN;

 	drvdata->gpio_data = devm_gpiod_get(dev, "data", gflags);
 	if (IS_ERR(drvdata->gpio_data)) {
 		dev_err(dev, "failed to request data gpio: %ld",
 			PTR_ERR(drvdata->gpio_data));
 		return PTR_ERR(drvdata->gpio_data);
 	}

 	drvdata->gpio_clk = devm_gpiod_get(dev, "clk", gflags);
 	if (IS_ERR(drvdata->gpio_clk)) {
 		dev_err(dev, "failed to request clock gpio: %ld",
 			PTR_ERR(drvdata->gpio_clk));
 		return PTR_ERR(drvdata->gpio_clk);
 	}

 	drvdata->write_enable = device_property_read_bool(dev,
 				"write-enable");

 	return 0;
 }

 static int ps2_gpio_probe(struct platform_device *pdev)
 {
 	struct ps2_gpio_data *drvdata;
 	struct serio *serio;
 	struct device *dev = &pdev->dev;
 	int error;

 	drvdata = devm_kzalloc(dev, sizeof(struct ps2_gpio_data), GFP_KERNEL);
 	serio = kzalloc(sizeof(struct serio), GFP_KERNEL);
 	if (!drvdata || !serio) {
 		error = -ENOMEM;
 		goto err_free_serio;
 	}

 	error = ps2_gpio_get_props(dev, drvdata);
 	if (error)
 		goto err_free_serio;

 	if (gpiod_cansleep(drvdata->gpio_data) ||
 	    gpiod_cansleep(drvdata->gpio_clk)) {
 		dev_err(dev, "GPIO data or clk are connected via slow bus\n");
 		error = -EINVAL;
 		goto err_free_serio;
 	}

 	drvdata->irq = platform_get_irq(pdev, 0);
 	if (drvdata->irq < 0) {
 		error = drvdata->irq;
 		goto err_free_serio;
 	}

 	error = devm_request_irq(dev, drvdata->irq, ps2_gpio_irq,
 				 IRQF_NO_THREAD, DRIVER_NAME, drvdata);
 	if (error) {
 		dev_err(dev, "failed to request irq %d: %d\n",
 			drvdata->irq, error);
 		goto err_free_serio;
 	}

 	/* Keep irq disabled until serio->open is called. */
 	disable_irq(drvdata->irq);

 	serio->id.type = SERIO_8042;
 	serio->open = ps2_gpio_open;
 	serio->close = ps2_gpio_close;
 	/*
 	 * Write can be enabled in platform/dt data, but possibly it will not
 	 * work because of the tough timings.
 	 */
 	serio->write = drvdata->write_enable ? ps2_gpio_write : NULL;
 	serio->port_data = drvdata;
 	serio->dev.parent = dev;
 	strlcpy(serio->name, dev_name(dev), sizeof(serio->name));
 	strlcpy(serio->phys, dev_name(dev), sizeof(serio->phys));

 	drvdata->serio = serio;
 	drvdata->dev = dev;
 	drvdata->mode = PS2_MODE_RX;

 	/*
 	 * Tx count always starts at 1, as the start bit is sent implicitly by
 	 * host-to-device communication initialization.
 	 */
 	drvdata->tx.cnt = 1;

 	INIT_DELAYED_WORK(&drvdata->tx.work, ps2_gpio_tx_work_fn);
 	init_completion(&drvdata->tx.complete);
 	mutex_init(&drvdata->tx.mutex);

 	serio_register_port(serio);
 	platform_set_drvdata(pdev, drvdata);

 	return 0;	/* success */

 err_free_serio:
 	kfree(serio);
 	return error;
 }

 static int ps2_gpio_remove(struct platform_device *pdev)
 {
 	struct ps2_gpio_data *drvdata = platform_get_drvdata(pdev);

 	serio_unregister_port(drvdata->serio);
 	return 0;
 }

 #if defined(CONFIG_OF)
 static const struct of_device_id ps2_gpio_match[] = {
 	{ .compatible = "ps2-gpio", },
 	{ },
 };
 MODULE_DEVICE_TABLE(of, ps2_gpio_match);
 #endif

 static struct platform_driver ps2_gpio_driver = {
 	.probe		= ps2_gpio_probe,
 	.remove		= ps2_gpio_remove,
 	.driver = {
 		.name = DRIVER_NAME,
 		.of_match_table = of_match_ptr(ps2_gpio_match),
 	},
 };
 module_platform_driver(ps2_gpio_driver);

 MODULE_AUTHOR("Danilo Krummrich <danilokrummrich@dk-develop.de>");
 MODULE_DESCRIPTION("GPIO PS2 driver");
 MODULE_LICENSE("GPL v2");
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* GPIO based serio bus driver for bit banging the PS/2 protocol
	*
	* Author: Danilo Krummrich <danilokrummrich@dk-develop.de>
	*/

	#include <linux/gpio/consumer.h>
	#include <linux/interrupt.h>
	#include <linux/module.h>
	#include <linux/serio.h>
	#include <linux/slab.h>
	#include <linux/platform_device.h>
	#include <linux/workqueue.h>
	#include <linux/completion.h>
	#include <linux/mutex.h>
	#include <linux/preempt.h>
	#include <linux/property.h>
	#include <linux/of.h>
	#include <linux/jiffies.h>
	#include <linux/delay.h>
	#include <linux/timekeeping.h>

	#define DRIVER_NAME "ps2-gpio"

	#define PS2_MODE_RX 0
	#define PS2_MODE_TX 1

	#define PS2_START_BIT 0
	#define PS2_DATA_BIT0 1
	#define PS2_DATA_BIT1 2
	#define PS2_DATA_BIT2 3
	#define PS2_DATA_BIT3 4
	#define PS2_DATA_BIT4 5
	#define PS2_DATA_BIT5 6
	#define PS2_DATA_BIT6 7
	#define PS2_DATA_BIT7 8
	#define PS2_PARITY_BIT 9
	#define PS2_STOP_BIT 10
	#define PS2_ACK_BIT 11

	#define PS2_DEV_RET_ACK 0xfa
	#define PS2_DEV_RET_NACK 0xfe

	#define PS2_CMD_RESEND 0xfe

	/*
	* The PS2 protocol specifies a clock frequency between 10kHz and 16.7kHz,
	* therefore the maximal interrupt interval should be 100us and the minimum
	* interrupt interval should be ~60us. Let's allow +/- 20us for frequency
	* deviations and interrupt latency.
	*
	* The data line must be samples after ~30us to 50us after the falling edge,
	* since the device updates the data line at the rising edge.
	*
	* ___ ______ ______ ______ ___
	* \ / \ / \ / \ /
	* \ / \ / \ / \ /
	* \______/ \______/ \______/ \______/
	*
	* \|-----------------\| \|--------\|
	* 60us/100us 30us/50us
	*/
	#define PS2_CLK_FREQ_MIN_HZ 10000
	#define PS2_CLK_FREQ_MAX_HZ 16700
	#define PS2_CLK_MIN_INTERVAL_US ((1000 * 1000) / PS2_CLK_FREQ_MAX_HZ)
	#define PS2_CLK_MAX_INTERVAL_US ((1000 * 1000) / PS2_CLK_FREQ_MIN_HZ)
	#define PS2_IRQ_MIN_INTERVAL_US (PS2_CLK_MIN_INTERVAL_US - 20)
	#define PS2_IRQ_MAX_INTERVAL_US (PS2_CLK_MAX_INTERVAL_US + 20)

	struct ps2_gpio_data {
	struct device *dev;
	struct serio *serio;
	unsigned char mode;
	struct gpio_desc *gpio_clk;
	struct gpio_desc *gpio_data;
	bool write_enable;
	int irq;
	ktime_t t_irq_now;
	ktime_t t_irq_last;
	struct {
	unsigned char cnt;
	unsigned char byte;
	} rx;
	struct {
	unsigned char cnt;
	unsigned char byte;
	ktime_t t_xfer_start;
	ktime_t t_xfer_end;
	struct completion complete;
	struct mutex mutex;
	struct delayed_work work;
	} tx;
	};

	static int ps2_gpio_open(struct serio *serio)
	{
	struct ps2_gpio_data *drvdata = serio->port_data;

	drvdata->t_irq_last = 0;
	drvdata->tx.t_xfer_end = 0;

	enable_irq(drvdata->irq);
	return 0;
	}

	static void ps2_gpio_close(struct serio *serio)
	{
	struct ps2_gpio_data *drvdata = serio->port_data;

	flush_delayed_work(&drvdata->tx.work);
	disable_irq(drvdata->irq);
	}

	static int __ps2_gpio_write(struct serio *serio, unsigned char val)
	{
	struct ps2_gpio_data *drvdata = serio->port_data;

	disable_irq_nosync(drvdata->irq);
	gpiod_direction_output(drvdata->gpio_clk, 0);

	drvdata->mode = PS2_MODE_TX;
	drvdata->tx.byte = val;

	schedule_delayed_work(&drvdata->tx.work, usecs_to_jiffies(200));

	return 0;
	}

	static int ps2_gpio_write(struct serio *serio, unsigned char val)
	{
	struct ps2_gpio_data *drvdata = serio->port_data;
	int ret = 0;

	if (in_task()) {
	mutex_lock(&drvdata->tx.mutex);
	__ps2_gpio_write(serio, val);
	if (!wait_for_completion_timeout(&drvdata->tx.complete,
	msecs_to_jiffies(10000)))
	ret = SERIO_TIMEOUT;
	mutex_unlock(&drvdata->tx.mutex);
	} else {
	__ps2_gpio_write(serio, val);
	}

	return ret;
	}

	static void ps2_gpio_tx_work_fn(struct work_struct *work)
	{
	struct delayed_work *dwork = to_delayed_work(work);
	struct ps2_gpio_data *drvdata = container_of(dwork,
	struct ps2_gpio_data,
	tx.work);

	drvdata->tx.t_xfer_start = ktime_get();
	enable_irq(drvdata->irq);
	gpiod_direction_output(drvdata->gpio_data, 0);
	gpiod_direction_input(drvdata->gpio_clk);
	}

	static irqreturn_t ps2_gpio_irq_rx(struct ps2_gpio_data *drvdata)
	{
	unsigned char byte, cnt;
	int data;
	int rxflags = 0;
	s64 us_delta;

	byte = drvdata->rx.byte;
	cnt = drvdata->rx.cnt;

	drvdata->t_irq_now = ktime_get();

	/*
	* We need to consider spurious interrupts happening right after
	* a TX xfer finished.
	*/
	us_delta = ktime_us_delta(drvdata->t_irq_now, drvdata->tx.t_xfer_end);
	if (unlikely(us_delta < PS2_IRQ_MIN_INTERVAL_US))
	goto end;

	us_delta = ktime_us_delta(drvdata->t_irq_now, drvdata->t_irq_last);
	if (us_delta > PS2_IRQ_MAX_INTERVAL_US && cnt) {
	dev_err(drvdata->dev,
	"RX: timeout, probably we missed an interrupt\n");
	goto err;
	} else if (unlikely(us_delta < PS2_IRQ_MIN_INTERVAL_US)) {
	/* Ignore spurious IRQs. */
	goto end;
	}
	drvdata->t_irq_last = drvdata->t_irq_now;

	data = gpiod_get_value(drvdata->gpio_data);
	if (unlikely(data < 0)) {
	dev_err(drvdata->dev, "RX: failed to get data gpio val: %d\n",
	data);
	goto err;
	}

	switch (cnt) {
	case PS2_START_BIT:
	/* start bit should be low */
	if (unlikely(data)) {
	dev_err(drvdata->dev, "RX: start bit should be low\n");
	goto err;
	}
	break;
	case PS2_DATA_BIT0:
	case PS2_DATA_BIT1:
	case PS2_DATA_BIT2:
	case PS2_DATA_BIT3:
	case PS2_DATA_BIT4:
	case PS2_DATA_BIT5:
	case PS2_DATA_BIT6:
	case PS2_DATA_BIT7:
	/* processing data bits */
	if (data)
	byte \|= (data << (cnt - 1));
	break;
	case PS2_PARITY_BIT:
	/* check odd parity */
	if (!((hweight8(byte) & 1) ^ data)) {
	rxflags \|= SERIO_PARITY;
	dev_warn(drvdata->dev, "RX: parity error\n");
	if (!drvdata->write_enable)
	goto err;
	}
	break;
	case PS2_STOP_BIT:
	/* stop bit should be high */
	if (unlikely(!data)) {
	dev_err(drvdata->dev, "RX: stop bit should be high\n");
	goto err;
	}

	/*
	* Do not send spurious ACK's and NACK's when write fn is
	* not provided.
	*/
	if (!drvdata->write_enable) {
	if (byte == PS2_DEV_RET_NACK)
	goto err;
	else if (byte == PS2_DEV_RET_ACK)
	break;
	}

	serio_interrupt(drvdata->serio, byte, rxflags);
	dev_dbg(drvdata->dev, "RX: sending byte 0x%x\n", byte);

	cnt = byte = 0;

	goto end; /* success */
	default:
	dev_err(drvdata->dev, "RX: got out of sync with the device\n");
	goto err;
	}

	cnt++;
	goto end; /* success */

	err:
	cnt = byte = 0;
	__ps2_gpio_write(drvdata->serio, PS2_CMD_RESEND);
	end:
	drvdata->rx.cnt = cnt;
	drvdata->rx.byte = byte;
	return IRQ_HANDLED;
	}

	static irqreturn_t ps2_gpio_irq_tx(struct ps2_gpio_data *drvdata)
	{
	unsigned char byte, cnt;
	int data;
	s64 us_delta;

	cnt = drvdata->tx.cnt;
	byte = drvdata->tx.byte;

	drvdata->t_irq_now = ktime_get();

	/*
	* There might be pending IRQs since we disabled IRQs in
	* __ps2_gpio_write(). We can expect at least one clock period until
	* the device generates the first falling edge after releasing the
	* clock line.
	*/
	us_delta = ktime_us_delta(drvdata->t_irq_now,
	drvdata->tx.t_xfer_start);
	if (unlikely(us_delta < PS2_CLK_MIN_INTERVAL_US))
	goto end;

	us_delta = ktime_us_delta(drvdata->t_irq_now, drvdata->t_irq_last);
	if (us_delta > PS2_IRQ_MAX_INTERVAL_US && cnt > 1) {
	dev_err(drvdata->dev,
	"TX: timeout, probably we missed an interrupt\n");
	goto err;
	} else if (unlikely(us_delta < PS2_IRQ_MIN_INTERVAL_US)) {
	/* Ignore spurious IRQs. */
	goto end;
	}
	drvdata->t_irq_last = drvdata->t_irq_now;

	switch (cnt) {
	case PS2_START_BIT:
	/* should never happen */
	dev_err(drvdata->dev,
	"TX: start bit should have been sent already\n");
	goto err;
	case PS2_DATA_BIT0:
	case PS2_DATA_BIT1:
	case PS2_DATA_BIT2:
	case PS2_DATA_BIT3:
	case PS2_DATA_BIT4:
	case PS2_DATA_BIT5:
	case PS2_DATA_BIT6:
	case PS2_DATA_BIT7:
	data = byte & BIT(cnt - 1);
	gpiod_set_value(drvdata->gpio_data, data);
	break;
	case PS2_PARITY_BIT:
	/* do odd parity */
	data = !(hweight8(byte) & 1);
	gpiod_set_value(drvdata->gpio_data, data);
	break;
	case PS2_STOP_BIT:
	/* release data line to generate stop bit */
	gpiod_direction_input(drvdata->gpio_data);
	break;
	case PS2_ACK_BIT:
	data = gpiod_get_value(drvdata->gpio_data);
	if (data) {
	dev_warn(drvdata->dev, "TX: received NACK, retry\n");
	goto err;
	}

	drvdata->tx.t_xfer_end = ktime_get();
	drvdata->mode = PS2_MODE_RX;
	complete(&drvdata->tx.complete);

	cnt = 1;
	goto end; /* success */
	default:
	/*
	* Probably we missed the stop bit. Therefore we release data
	* line and try again.
	*/
	gpiod_direction_input(drvdata->gpio_data);
	dev_err(drvdata->dev, "TX: got out of sync with the device\n");
	goto err;
	}

	cnt++;
	goto end; /* success */

	err:
	cnt = 1;
	gpiod_direction_input(drvdata->gpio_data);
	__ps2_gpio_write(drvdata->serio, drvdata->tx.byte);
	end:
	drvdata->tx.cnt = cnt;
	return IRQ_HANDLED;
	}

	static irqreturn_t ps2_gpio_irq(int irq, void *dev_id)
	{
	struct ps2_gpio_data *drvdata = dev_id;

	return drvdata->mode ? ps2_gpio_irq_tx(drvdata) :
	ps2_gpio_irq_rx(drvdata);
	}

	static int ps2_gpio_get_props(struct device *dev,
	struct ps2_gpio_data *drvdata)
	{
	enum gpiod_flags gflags;

	/* Enforce open drain, since this is required by the PS/2 bus. */
	gflags = GPIOD_IN \| GPIOD_FLAGS_BIT_OPEN_DRAIN;

	drvdata->gpio_data = devm_gpiod_get(dev, "data", gflags);
	if (IS_ERR(drvdata->gpio_data)) {
	dev_err(dev, "failed to request data gpio: %ld",
	PTR_ERR(drvdata->gpio_data));
	return PTR_ERR(drvdata->gpio_data);
	}

	drvdata->gpio_clk = devm_gpiod_get(dev, "clk", gflags);
	if (IS_ERR(drvdata->gpio_clk)) {
	dev_err(dev, "failed to request clock gpio: %ld",
	PTR_ERR(drvdata->gpio_clk));
	return PTR_ERR(drvdata->gpio_clk);
	}

	drvdata->write_enable = device_property_read_bool(dev,
	"write-enable");

	return 0;
	}

	static int ps2_gpio_probe(struct platform_device *pdev)
	{
	struct ps2_gpio_data *drvdata;
	struct serio *serio;
	struct device *dev = &pdev->dev;
	int error;

	drvdata = devm_kzalloc(dev, sizeof(struct ps2_gpio_data), GFP_KERNEL);
	serio = kzalloc(sizeof(struct serio), GFP_KERNEL);
	if (!drvdata \|\| !serio) {
	error = -ENOMEM;
	goto err_free_serio;
	}

	error = ps2_gpio_get_props(dev, drvdata);
	if (error)
	goto err_free_serio;

	if (gpiod_cansleep(drvdata->gpio_data) \|\|
	gpiod_cansleep(drvdata->gpio_clk)) {
	dev_err(dev, "GPIO data or clk are connected via slow bus\n");
	error = -EINVAL;
	goto err_free_serio;
	}

	drvdata->irq = platform_get_irq(pdev, 0);
	if (drvdata->irq < 0) {
	error = drvdata->irq;
	goto err_free_serio;
	}

	error = devm_request_irq(dev, drvdata->irq, ps2_gpio_irq,
	IRQF_NO_THREAD, DRIVER_NAME, drvdata);
	if (error) {
	dev_err(dev, "failed to request irq %d: %d\n",
	drvdata->irq, error);
	goto err_free_serio;
	}

	/* Keep irq disabled until serio->open is called. */
	disable_irq(drvdata->irq);

	serio->id.type = SERIO_8042;
	serio->open = ps2_gpio_open;
	serio->close = ps2_gpio_close;
	/*
	* Write can be enabled in platform/dt data, but possibly it will not
	* work because of the tough timings.
	*/
	serio->write = drvdata->write_enable ? ps2_gpio_write : NULL;
	serio->port_data = drvdata;
	serio->dev.parent = dev;
	strlcpy(serio->name, dev_name(dev), sizeof(serio->name));
	strlcpy(serio->phys, dev_name(dev), sizeof(serio->phys));

	drvdata->serio = serio;
	drvdata->dev = dev;
	drvdata->mode = PS2_MODE_RX;

	/*
	* Tx count always starts at 1, as the start bit is sent implicitly by
	* host-to-device communication initialization.
	*/
	drvdata->tx.cnt = 1;

	INIT_DELAYED_WORK(&drvdata->tx.work, ps2_gpio_tx_work_fn);
	init_completion(&drvdata->tx.complete);
	mutex_init(&drvdata->tx.mutex);

	serio_register_port(serio);
	platform_set_drvdata(pdev, drvdata);

	return 0; /* success */

	err_free_serio:
	kfree(serio);
	return error;
	}

	static int ps2_gpio_remove(struct platform_device *pdev)
	{
	struct ps2_gpio_data *drvdata = platform_get_drvdata(pdev);

	serio_unregister_port(drvdata->serio);
	return 0;
	}

	#if defined(CONFIG_OF)
	static const struct of_device_id ps2_gpio_match[] = {
	{ .compatible = "ps2-gpio", },
	{ },
	};
	MODULE_DEVICE_TABLE(of, ps2_gpio_match);
	#endif

	static struct platform_driver ps2_gpio_driver = {
	.probe = ps2_gpio_probe,
	.remove = ps2_gpio_remove,
	.driver = {
	.name = DRIVER_NAME,
	.of_match_table = of_match_ptr(ps2_gpio_match),
	},
	};
	module_platform_driver(ps2_gpio_driver);

	MODULE_AUTHOR("Danilo Krummrich <danilokrummrich@dk-develop.de>");
	MODULE_DESCRIPTION("GPIO PS2 driver");
	MODULE_LICENSE("GPL v2");