/*
 * GPIO driver for the ACCES 104-IDI-48 family
 * Copyright (C) 2015 William Breathitt Gray
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License, version 2, as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 */
#include <linux/bitops.h>
#include <linux/device.h>
#include <linux/errno.h>
#include <linux/gpio/driver.h>
#include <linux/io.h>
#include <linux/ioport.h>
#include <linux/interrupt.h>
#include <linux/irqdesc.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/platform_device.h>
#include <linux/spinlock.h>

static unsigned idi_48_base;
module_param(idi_48_base, uint, 0);
MODULE_PARM_DESC(idi_48_base, "ACCES 104-IDI-48 base address");
static unsigned idi_48_irq;
module_param(idi_48_irq, uint, 0);
MODULE_PARM_DESC(idi_48_irq, "ACCES 104-IDI-48 interrupt line number");

/**
 * struct idi_48_gpio - GPIO device private data structure
 * @chip:	instance of the gpio_chip
 * @lock:	synchronization lock to prevent I/O race conditions
 * @ack_lock:	synchronization lock to prevent IRQ handler race conditions
 * @irq_mask:	input bits affected by interrupts
 * @base:	base port address of the GPIO device
 * @irq:	Interrupt line number
 * @cos_enb:	Change-Of-State IRQ enable boundaries mask
 */
struct idi_48_gpio {
	struct gpio_chip chip;
	spinlock_t lock;
	spinlock_t ack_lock;
	unsigned char irq_mask[6];
	unsigned base;
	unsigned irq;
	unsigned char cos_enb;
};

static int idi_48_gpio_get_direction(struct gpio_chip *chip, unsigned offset)
{
	return 1;
}

static int idi_48_gpio_direction_input(struct gpio_chip *chip, unsigned offset)
{
	return 0;
}

static int idi_48_gpio_get(struct gpio_chip *chip, unsigned offset)
{
	struct idi_48_gpio *const idi48gpio = gpiochip_get_data(chip);
	unsigned i;
	const unsigned register_offset[6] = { 0, 1, 2, 4, 5, 6 };
	unsigned base_offset;
	unsigned mask;

	for (i = 0; i < 48; i += 8)
		if (offset < i + 8) {
			base_offset = register_offset[i / 8];
			mask = BIT(offset - i);

			return !!(inb(idi48gpio->base + base_offset) & mask);
		}

	/* The following line should never execute since offset < 48 */
	return 0;
}

static void idi_48_irq_ack(struct irq_data *data)
{
}

static void idi_48_irq_mask(struct irq_data *data)
{
	struct gpio_chip *chip = irq_data_get_irq_chip_data(data);
	struct idi_48_gpio *const idi48gpio = gpiochip_get_data(chip);
	const unsigned offset = irqd_to_hwirq(data);
	unsigned i;
	unsigned mask;
	unsigned boundary;
	unsigned long flags;

	for (i = 0; i < 48; i += 8)
		if (offset < i + 8) {
			mask = BIT(offset - i);
			boundary = i / 8;

			idi48gpio->irq_mask[boundary] &= ~mask;

			if (!idi48gpio->irq_mask[boundary]) {
				idi48gpio->cos_enb &= ~BIT(boundary);

				spin_lock_irqsave(&idi48gpio->lock, flags);

				outb(idi48gpio->cos_enb, idi48gpio->base + 7);

				spin_unlock_irqrestore(&idi48gpio->lock, flags);
			}

			return;
		}
}

static void idi_48_irq_unmask(struct irq_data *data)
{
	struct gpio_chip *chip = irq_data_get_irq_chip_data(data);
	struct idi_48_gpio *const idi48gpio = gpiochip_get_data(chip);
	const unsigned offset = irqd_to_hwirq(data);
	unsigned i;
	unsigned mask;
	unsigned boundary;
	unsigned prev_irq_mask;
	unsigned long flags;

	for (i = 0; i < 48; i += 8)
		if (offset < i + 8) {
			mask = BIT(offset - i);
			boundary = i / 8;
			prev_irq_mask = idi48gpio->irq_mask[boundary];

			idi48gpio->irq_mask[boundary] |= mask;

			if (!prev_irq_mask) {
				idi48gpio->cos_enb |= BIT(boundary);

				spin_lock_irqsave(&idi48gpio->lock, flags);

				outb(idi48gpio->cos_enb, idi48gpio->base + 7);

				spin_unlock_irqrestore(&idi48gpio->lock, flags);
			}

			return;
		}
}

static int idi_48_irq_set_type(struct irq_data *data, unsigned flow_type)
{
	/* The only valid irq types are none and both-edges */
	if (flow_type != IRQ_TYPE_NONE &&
		(flow_type & IRQ_TYPE_EDGE_BOTH) != IRQ_TYPE_EDGE_BOTH)
		return -EINVAL;

	return 0;
}

static struct irq_chip idi_48_irqchip = {
	.name = "104-idi-48",
	.irq_ack = idi_48_irq_ack,
	.irq_mask = idi_48_irq_mask,
	.irq_unmask = idi_48_irq_unmask,
	.irq_set_type = idi_48_irq_set_type
};

static irqreturn_t idi_48_irq_handler(int irq, void *dev_id)
{
	struct idi_48_gpio *const idi48gpio = dev_id;
	unsigned long cos_status;
	unsigned long boundary;
	unsigned long irq_mask;
	unsigned long bit_num;
	unsigned long gpio;
	struct gpio_chip *const chip = &idi48gpio->chip;

	spin_lock(&idi48gpio->ack_lock);

	spin_lock(&idi48gpio->lock);

	cos_status = inb(idi48gpio->base + 7);

	spin_unlock(&idi48gpio->lock);

	/* IRQ Status (bit 6) is active low (0 = IRQ generated by device) */
	if (cos_status & BIT(6)) {
		spin_unlock(&idi48gpio->ack_lock);
		return IRQ_NONE;
	}

	/* Bit 0-5 indicate which Change-Of-State boundary triggered the IRQ */
	cos_status &= 0x3F;

	for_each_set_bit(boundary, &cos_status, 6) {
		irq_mask = idi48gpio->irq_mask[boundary];

		for_each_set_bit(bit_num, &irq_mask, 8) {
			gpio = bit_num + boundary * 8;

			generic_handle_irq(irq_find_mapping(chip->irqdomain,
				gpio));
		}
	}

	spin_unlock(&idi48gpio->ack_lock);

	return IRQ_HANDLED;
}

static int __init idi_48_probe(struct platform_device *pdev)
{
	struct device *dev = &pdev->dev;
	struct idi_48_gpio *idi48gpio;
	const unsigned base = idi_48_base;
	const unsigned extent = 8;
	const char *const name = dev_name(dev);
	int err;
	const unsigned irq = idi_48_irq;

	idi48gpio = devm_kzalloc(dev, sizeof(*idi48gpio), GFP_KERNEL);
	if (!idi48gpio)
		return -ENOMEM;

	if (!devm_request_region(dev, base, extent, name)) {
		dev_err(dev, "Unable to lock port addresses (0x%X-0x%X)\n",
			base, base + extent);
		return -EBUSY;
	}

	idi48gpio->chip.label = name;
	idi48gpio->chip.parent = dev;
	idi48gpio->chip.owner = THIS_MODULE;
	idi48gpio->chip.base = -1;
	idi48gpio->chip.ngpio = 48;
	idi48gpio->chip.get_direction = idi_48_gpio_get_direction;
	idi48gpio->chip.direction_input = idi_48_gpio_direction_input;
	idi48gpio->chip.get = idi_48_gpio_get;
	idi48gpio->base = base;
	idi48gpio->irq = irq;

	spin_lock_init(&idi48gpio->lock);

	dev_set_drvdata(dev, idi48gpio);

	err = gpiochip_add_data(&idi48gpio->chip, idi48gpio);
	if (err) {
		dev_err(dev, "GPIO registering failed (%d)\n", err);
		return err;
	}

	/* Disable IRQ by default */
	outb(0, base + 7);
	inb(base + 7);

	err = gpiochip_irqchip_add(&idi48gpio->chip, &idi_48_irqchip, 0,
		handle_edge_irq, IRQ_TYPE_NONE);
	if (err) {
		dev_err(dev, "Could not add irqchip (%d)\n", err);
		goto err_gpiochip_remove;
	}

	err = request_irq(irq, idi_48_irq_handler, IRQF_SHARED, name,
		idi48gpio);
	if (err) {
		dev_err(dev, "IRQ handler registering failed (%d)\n", err);
		goto err_gpiochip_remove;
	}

	return 0;

err_gpiochip_remove:
	gpiochip_remove(&idi48gpio->chip);
	return err;
}

static int idi_48_remove(struct platform_device *pdev)
{
	struct idi_48_gpio *const idi48gpio = platform_get_drvdata(pdev);

	free_irq(idi48gpio->irq, idi48gpio);
	gpiochip_remove(&idi48gpio->chip);

	return 0;
}

static struct platform_device *idi_48_device;

static struct platform_driver idi_48_driver = {
	.driver = {
		.name = "104-idi-48"
	},
	.remove = idi_48_remove
};

static void __exit idi_48_exit(void)
{
	platform_device_unregister(idi_48_device);
	platform_driver_unregister(&idi_48_driver);
}

static int __init idi_48_init(void)
{
	int err;

	idi_48_device = platform_device_alloc(idi_48_driver.driver.name, -1);
	if (!idi_48_device)
		return -ENOMEM;

	err = platform_device_add(idi_48_device);
	if (err)
		goto err_platform_device;

	err = platform_driver_probe(&idi_48_driver, idi_48_probe);
	if (err)
		goto err_platform_driver;

	return 0;

err_platform_driver:
	platform_device_del(idi_48_device);
err_platform_device:
	platform_device_put(idi_48_device);
	return err;
}

module_init(idi_48_init);
module_exit(idi_48_exit);

MODULE_AUTHOR("William Breathitt Gray <vilhelm.gray@gmail.com>");
MODULE_DESCRIPTION("ACCES 104-IDI-48 GPIO driver");
MODULE_LICENSE("GPL v2");