// SPDX-License-Identifier: GPL-2.0-only
/*
 * TQC PS/2 Multiplexer driver
 *
 * Copyright (C) 2010 Dmitry Eremin-Solenikov
 */


#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/serio.h>

MODULE_AUTHOR("Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>");
MODULE_DESCRIPTION("TQC PS/2 Multiplexer driver");
MODULE_LICENSE("GPL");

#define PS2MULT_KB_SELECTOR		0xA0
#define PS2MULT_MS_SELECTOR		0xA1
#define PS2MULT_ESCAPE			0x7D
#define PS2MULT_BSYNC			0x7E
#define PS2MULT_SESSION_START		0x55
#define PS2MULT_SESSION_END		0x56

struct ps2mult_port {
	struct serio *serio;
	unsigned char sel;
	bool registered;
};

#define PS2MULT_NUM_PORTS	2
#define PS2MULT_KBD_PORT	0
#define PS2MULT_MOUSE_PORT	1

struct ps2mult {
	struct serio *mx_serio;
	struct ps2mult_port ports[PS2MULT_NUM_PORTS];

	spinlock_t lock;
	struct ps2mult_port *in_port;
	struct ps2mult_port *out_port;
	bool escape;
};

/* First MUST come PS2MULT_NUM_PORTS selectors */
static const unsigned char ps2mult_controls[] = {
	PS2MULT_KB_SELECTOR, PS2MULT_MS_SELECTOR,
	PS2MULT_ESCAPE, PS2MULT_BSYNC,
	PS2MULT_SESSION_START, PS2MULT_SESSION_END,
};

static const struct serio_device_id ps2mult_serio_ids[] = {
	{
		.type	= SERIO_RS232,
		.proto	= SERIO_PS2MULT,
		.id	= SERIO_ANY,
		.extra	= SERIO_ANY,
	},
	{ 0 }
};

MODULE_DEVICE_TABLE(serio, ps2mult_serio_ids);

static void ps2mult_select_port(struct ps2mult *psm, struct ps2mult_port *port)
{
	struct serio *mx_serio = psm->mx_serio;

	serio_write(mx_serio, port->sel);
	psm->out_port = port;
	dev_dbg(&mx_serio->dev, "switched to sel %02x\n", port->sel);
}

static int ps2mult_serio_write(struct serio *serio, unsigned char data)
{
	struct serio *mx_port = serio->parent;
	struct ps2mult *psm = serio_get_drvdata(mx_port);
	struct ps2mult_port *port = serio->port_data;
	bool need_escape;

	guard(spinlock_irqsave)(&psm->lock);

	if (psm->out_port != port)
		ps2mult_select_port(psm, port);

	need_escape = memchr(ps2mult_controls, data, sizeof(ps2mult_controls));

	dev_dbg(&serio->dev,
		"write: %s%02x\n", need_escape ? "ESC " : "", data);

	if (need_escape)
		serio_write(mx_port, PS2MULT_ESCAPE);

	serio_write(mx_port, data);

	return 0;
}

static int ps2mult_serio_start(struct serio *serio)
{
	struct ps2mult *psm = serio_get_drvdata(serio->parent);
	struct ps2mult_port *port = serio->port_data;

	guard(spinlock_irqsave)(&psm->lock);

	port->registered = true;

	return 0;
}

static void ps2mult_serio_stop(struct serio *serio)
{
	struct ps2mult *psm = serio_get_drvdata(serio->parent);
	struct ps2mult_port *port = serio->port_data;

	guard(spinlock_irqsave)(&psm->lock);

	port->registered = false;
}

static int ps2mult_create_port(struct ps2mult *psm, int i)
{
	struct serio *mx_serio = psm->mx_serio;
	struct serio *serio;

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

	strscpy(serio->name, "TQC PS/2 Multiplexer", sizeof(serio->name));
	snprintf(serio->phys, sizeof(serio->phys),
		 "%s/port%d", mx_serio->phys, i);
	serio->id.type = SERIO_8042;
	serio->write = ps2mult_serio_write;
	serio->start = ps2mult_serio_start;
	serio->stop = ps2mult_serio_stop;
	serio->parent = psm->mx_serio;
	serio->port_data = &psm->ports[i];

	psm->ports[i].serio = serio;

	return 0;
}

static void ps2mult_reset(struct ps2mult *psm)
{
	guard(spinlock_irqsave)(&psm->lock);

	serio_write(psm->mx_serio, PS2MULT_SESSION_END);
	serio_write(psm->mx_serio, PS2MULT_SESSION_START);

	ps2mult_select_port(psm, &psm->ports[PS2MULT_KBD_PORT]);
}

static int ps2mult_connect(struct serio *serio, struct serio_driver *drv)
{
	struct ps2mult *psm;
	int i;
	int error;

	if (!serio->write)
		return -EINVAL;

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

	spin_lock_init(&psm->lock);
	psm->mx_serio = serio;

	for (i = 0; i < PS2MULT_NUM_PORTS; i++) {
		psm->ports[i].sel = ps2mult_controls[i];
		error = ps2mult_create_port(psm, i);
		if (error)
			goto err_out;
	}

	psm->in_port = psm->out_port = &psm->ports[PS2MULT_KBD_PORT];

	serio_set_drvdata(serio, psm);
	error = serio_open(serio, drv);
	if (error)
		goto err_out;

	ps2mult_reset(psm);

	for (i = 0; i <  PS2MULT_NUM_PORTS; i++) {
		struct serio *s = psm->ports[i].serio;

		dev_info(&serio->dev, "%s port at %s\n", s->name, serio->phys);
		serio_register_port(s);
	}

	return 0;

err_out:
	while (--i >= 0)
		kfree(psm->ports[i].serio);
	kfree(psm);
	return error;
}

static void ps2mult_disconnect(struct serio *serio)
{
	struct ps2mult *psm = serio_get_drvdata(serio);

	/* Note that serio core already take care of children ports */
	serio_write(serio, PS2MULT_SESSION_END);
	serio_close(serio);
	kfree(psm);

	serio_set_drvdata(serio, NULL);
}

static int ps2mult_reconnect(struct serio *serio)
{
	struct ps2mult *psm = serio_get_drvdata(serio);

	ps2mult_reset(psm);

	return 0;
}

static irqreturn_t ps2mult_interrupt(struct serio *serio,
				     unsigned char data, unsigned int dfl)
{
	struct ps2mult *psm = serio_get_drvdata(serio);
	struct ps2mult_port *in_port;

	dev_dbg(&serio->dev, "Received %02x flags %02x\n", data, dfl);

	guard(spinlock_irqsave)(&psm->lock);

	if (psm->escape) {
		psm->escape = false;
		in_port = psm->in_port;
		if (in_port->registered)
			serio_interrupt(in_port->serio, data, dfl);
		goto out;
	}

	switch (data) {
	case PS2MULT_ESCAPE:
		dev_dbg(&serio->dev, "ESCAPE\n");
		psm->escape = true;
		break;

	case PS2MULT_BSYNC:
		dev_dbg(&serio->dev, "BSYNC\n");
		psm->in_port = psm->out_port;
		break;

	case PS2MULT_SESSION_START:
		dev_dbg(&serio->dev, "SS\n");
		break;

	case PS2MULT_SESSION_END:
		dev_dbg(&serio->dev, "SE\n");
		break;

	case PS2MULT_KB_SELECTOR:
		dev_dbg(&serio->dev, "KB\n");
		psm->in_port = &psm->ports[PS2MULT_KBD_PORT];
		break;

	case PS2MULT_MS_SELECTOR:
		dev_dbg(&serio->dev, "MS\n");
		psm->in_port = &psm->ports[PS2MULT_MOUSE_PORT];
		break;

	default:
		in_port = psm->in_port;
		if (in_port->registered)
			serio_interrupt(in_port->serio, data, dfl);
		break;
	}

 out:
	return IRQ_HANDLED;
}

static struct serio_driver ps2mult_drv = {
	.driver		= {
		.name	= "ps2mult",
	},
	.description	= "TQC PS/2 Multiplexer driver",
	.id_table	= ps2mult_serio_ids,
	.interrupt	= ps2mult_interrupt,
	.connect	= ps2mult_connect,
	.disconnect	= ps2mult_disconnect,
	.reconnect	= ps2mult_reconnect,
};

module_serio_driver(ps2mult_drv);