/*
 *  linux/drivers/clocksource/zevio-timer.c
 *
 *  Copyright (C) 2013 Daniel Tang <tangrs@tangrs.id.au>
 *
 * 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.
 *
 */

#include <linux/io.h>
#include <linux/irq.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_irq.h>
#include <linux/clk.h>
#include <linux/clockchips.h>
#include <linux/cpumask.h>
#include <linux/interrupt.h>
#include <linux/slab.h>

#define IO_CURRENT_VAL	0x00
#define IO_DIVIDER	0x04
#define IO_CONTROL	0x08

#define IO_TIMER1	0x00
#define IO_TIMER2	0x0C

#define IO_MATCH_BEGIN	0x18
#define IO_MATCH(x)	(IO_MATCH_BEGIN + ((x) << 2))

#define IO_INTR_STS	0x00
#define IO_INTR_ACK	0x00
#define IO_INTR_MSK	0x04

#define CNTL_STOP_TIMER	(1 << 4)
#define CNTL_RUN_TIMER	(0 << 4)

#define CNTL_INC	(1 << 3)
#define CNTL_DEC	(0 << 3)

#define CNTL_TOZERO	0
#define CNTL_MATCH(x)	((x) + 1)
#define CNTL_FOREVER	7

/* There are 6 match registers but we only use one. */
#define TIMER_MATCH	0

#define TIMER_INTR_MSK	(1 << (TIMER_MATCH))
#define TIMER_INTR_ALL	0x3F

struct zevio_timer {
	void __iomem *base;
	void __iomem *timer1, *timer2;
	void __iomem *interrupt_regs;

	struct clk *clk;
	struct clock_event_device clkevt;
	struct irqaction clkevt_irq;

	char clocksource_name[64];
	char clockevent_name[64];
};

static int zevio_timer_set_event(unsigned long delta,
				 struct clock_event_device *dev)
{
	struct zevio_timer *timer = container_of(dev, struct zevio_timer,
						 clkevt);

	writel(delta, timer->timer1 + IO_CURRENT_VAL);
	writel(CNTL_RUN_TIMER | CNTL_DEC | CNTL_MATCH(TIMER_MATCH),
			timer->timer1 + IO_CONTROL);

	return 0;
}

static void zevio_timer_set_mode(enum clock_event_mode mode,
				 struct clock_event_device *dev)
{
	struct zevio_timer *timer = container_of(dev, struct zevio_timer,
						 clkevt);

	switch (mode) {
	case CLOCK_EVT_MODE_RESUME:
	case CLOCK_EVT_MODE_ONESHOT:
		/* Enable timer interrupts */
		writel(TIMER_INTR_MSK, timer->interrupt_regs + IO_INTR_MSK);
		writel(TIMER_INTR_ALL, timer->interrupt_regs + IO_INTR_ACK);
		break;
	case CLOCK_EVT_MODE_SHUTDOWN:
	case CLOCK_EVT_MODE_UNUSED:
		/* Disable timer interrupts */
		writel(0, timer->interrupt_regs + IO_INTR_MSK);
		writel(TIMER_INTR_ALL, timer->interrupt_regs + IO_INTR_ACK);
		/* Stop timer */
		writel(CNTL_STOP_TIMER, timer->timer1 + IO_CONTROL);
		break;
	case CLOCK_EVT_MODE_PERIODIC:
	default:
		/* Unsupported */
		break;
	}
}

static irqreturn_t zevio_timer_interrupt(int irq, void *dev_id)
{
	struct zevio_timer *timer = dev_id;
	u32 intr;

	intr = readl(timer->interrupt_regs + IO_INTR_ACK);
	if (!(intr & TIMER_INTR_MSK))
		return IRQ_NONE;

	writel(TIMER_INTR_MSK, timer->interrupt_regs + IO_INTR_ACK);
	writel(CNTL_STOP_TIMER, timer->timer1 + IO_CONTROL);

	if (timer->clkevt.event_handler)
		timer->clkevt.event_handler(&timer->clkevt);

	return IRQ_HANDLED;
}

static int __init zevio_timer_add(struct device_node *node)
{
	struct zevio_timer *timer;
	struct resource res;
	int irqnr, ret;

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

	timer->base = of_iomap(node, 0);
	if (!timer->base) {
		ret = -EINVAL;
		goto error_free;
	}
	timer->timer1 = timer->base + IO_TIMER1;
	timer->timer2 = timer->base + IO_TIMER2;

	timer->clk = of_clk_get(node, 0);
	if (IS_ERR(timer->clk)) {
		ret = PTR_ERR(timer->clk);
		pr_err("Timer clock not found! (error %d)\n", ret);
		goto error_unmap;
	}

	timer->interrupt_regs = of_iomap(node, 1);
	irqnr = irq_of_parse_and_map(node, 0);

	of_address_to_resource(node, 0, &res);
	scnprintf(timer->clocksource_name, sizeof(timer->clocksource_name),
			"%llx.%s_clocksource",
			(unsigned long long)res.start, node->name);

	scnprintf(timer->clockevent_name, sizeof(timer->clockevent_name),
			"%llx.%s_clockevent",
			(unsigned long long)res.start, node->name);

	if (timer->interrupt_regs && irqnr) {
		timer->clkevt.name		= timer->clockevent_name;
		timer->clkevt.set_next_event	= zevio_timer_set_event;
		timer->clkevt.set_mode		= zevio_timer_set_mode;
		timer->clkevt.rating		= 200;
		timer->clkevt.cpumask		= cpu_all_mask;
		timer->clkevt.features		= CLOCK_EVT_FEAT_ONESHOT;
		timer->clkevt.irq		= irqnr;

		writel(CNTL_STOP_TIMER, timer->timer1 + IO_CONTROL);
		writel(0, timer->timer1 + IO_DIVIDER);

		/* Start with timer interrupts disabled */
		writel(0, timer->interrupt_regs + IO_INTR_MSK);
		writel(TIMER_INTR_ALL, timer->interrupt_regs + IO_INTR_ACK);

		/* Interrupt to occur when timer value matches 0 */
		writel(0, timer->base + IO_MATCH(TIMER_MATCH));

		timer->clkevt_irq.name		= timer->clockevent_name;
		timer->clkevt_irq.handler	= zevio_timer_interrupt;
		timer->clkevt_irq.dev_id	= timer;
		timer->clkevt_irq.flags		= IRQF_TIMER | IRQF_IRQPOLL;

		setup_irq(irqnr, &timer->clkevt_irq);

		clockevents_config_and_register(&timer->clkevt,
				clk_get_rate(timer->clk), 0x0001, 0xffff);
		pr_info("Added %s as clockevent\n", timer->clockevent_name);
	}

	writel(CNTL_STOP_TIMER, timer->timer2 + IO_CONTROL);
	writel(0, timer->timer2 + IO_CURRENT_VAL);
	writel(0, timer->timer2 + IO_DIVIDER);
	writel(CNTL_RUN_TIMER | CNTL_FOREVER | CNTL_INC,
			timer->timer2 + IO_CONTROL);

	clocksource_mmio_init(timer->timer2 + IO_CURRENT_VAL,
			timer->clocksource_name,
			clk_get_rate(timer->clk),
			200, 16,
			clocksource_mmio_readw_up);

	pr_info("Added %s as clocksource\n", timer->clocksource_name);

	return 0;
error_unmap:
	iounmap(timer->base);
error_free:
	kfree(timer);
	return ret;
}

CLOCKSOURCE_OF_DECLARE(zevio_timer, "lsi,zevio-timer", zevio_timer_add);