linux/drivers/input/serio/ps2-gpio.c

// 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;
	strscpy(serio->name, dev_name(dev), sizeof(serio->name));
	strscpy(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");