/*
 * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
 * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
 * Copyright (C) 2012-2014 Cisco Systems
 * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Licensed under the GPL
 */

#include <linux/clockchips.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/jiffies.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/spinlock.h>
#include <linux/threads.h>
#include <asm/irq.h>
#include <asm/param.h>
#include <kern_util.h>
#include <os.h>
#include <timer-internal.h>
#include <shared/init.h>

#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
enum time_travel_mode time_travel_mode;
unsigned long long time_travel_time;
enum time_travel_timer_mode time_travel_timer_mode;
unsigned long long time_travel_timer_expiry;
unsigned long long time_travel_timer_interval;

static bool time_travel_start_set;
static unsigned long long time_travel_start;
#else
#define time_travel_start_set 0
#define time_travel_start 0
#endif

void timer_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
{
	unsigned long flags;

	if (time_travel_mode != TT_MODE_OFF)
		time_travel_set_time(time_travel_timer_expiry);

	local_irq_save(flags);
	do_IRQ(TIMER_IRQ, regs);
	local_irq_restore(flags);
}

static int itimer_shutdown(struct clock_event_device *evt)
{
	if (time_travel_mode != TT_MODE_OFF)
		time_travel_set_timer_mode(TT_TMR_DISABLED);

	if (time_travel_mode != TT_MODE_INFCPU)
		os_timer_disable();

	return 0;
}

static int itimer_set_periodic(struct clock_event_device *evt)
{
	unsigned long long interval = NSEC_PER_SEC / HZ;

	if (time_travel_mode != TT_MODE_OFF) {
		time_travel_set_timer_mode(TT_TMR_PERIODIC);
		time_travel_set_timer_expiry(time_travel_time + interval);
	}

	if (time_travel_mode != TT_MODE_INFCPU)
		os_timer_set_interval(interval);

	return 0;
}

static int itimer_next_event(unsigned long delta,
			     struct clock_event_device *evt)
{
	delta += 1;

	if (time_travel_mode != TT_MODE_OFF) {
		time_travel_set_timer_mode(TT_TMR_ONESHOT);
		time_travel_set_timer_expiry(time_travel_time + delta);
	}

	if (time_travel_mode != TT_MODE_INFCPU)
		return os_timer_one_shot(delta);

	return 0;
}

static int itimer_one_shot(struct clock_event_device *evt)
{
	return itimer_next_event(0, evt);
}

static struct clock_event_device timer_clockevent = {
	.name			= "posix-timer",
	.rating			= 250,
	.cpumask		= cpu_possible_mask,
	.features		= CLOCK_EVT_FEAT_PERIODIC |
				  CLOCK_EVT_FEAT_ONESHOT,
	.set_state_shutdown	= itimer_shutdown,
	.set_state_periodic	= itimer_set_periodic,
	.set_state_oneshot	= itimer_one_shot,
	.set_next_event		= itimer_next_event,
	.shift			= 0,
	.max_delta_ns		= 0xffffffff,
	.max_delta_ticks	= 0xffffffff,
	.min_delta_ns		= TIMER_MIN_DELTA,
	.min_delta_ticks	= TIMER_MIN_DELTA, // microsecond resolution should be enough for anyone, same as 640K RAM
	.irq			= 0,
	.mult			= 1,
};

static irqreturn_t um_timer(int irq, void *dev)
{
	if (get_current()->mm != NULL)
	{
        /* userspace - relay signal, results in correct userspace timers */
		os_alarm_process(get_current()->mm->context.id.u.pid);
	}

	(*timer_clockevent.event_handler)(&timer_clockevent);

	return IRQ_HANDLED;
}

static u64 timer_read(struct clocksource *cs)
{
	if (time_travel_mode != TT_MODE_OFF) {
		/*
		 * We make reading the timer cost a bit so that we don't get
		 * stuck in loops that expect time to move more than the
		 * exact requested sleep amount, e.g. python's socket server,
		 * see https://bugs.python.org/issue37026.
		 */
		time_travel_set_time(time_travel_time + TIMER_MULTIPLIER);
		return time_travel_time / TIMER_MULTIPLIER;
	}

	return os_nsecs() / TIMER_MULTIPLIER;
}

static struct clocksource timer_clocksource = {
	.name		= "timer",
	.rating		= 300,
	.read		= timer_read,
	.mask		= CLOCKSOURCE_MASK(64),
	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
};

static void __init um_timer_setup(void)
{
	int err;

	err = request_irq(TIMER_IRQ, um_timer, IRQF_TIMER, "hr timer", NULL);
	if (err != 0)
		printk(KERN_ERR "register_timer : request_irq failed - "
		       "errno = %d\n", -err);

	err = os_timer_create();
	if (err != 0) {
		printk(KERN_ERR "creation of timer failed - errno = %d\n", -err);
		return;
	}

	err = clocksource_register_hz(&timer_clocksource, NSEC_PER_SEC/TIMER_MULTIPLIER);
	if (err) {
		printk(KERN_ERR "clocksource_register_hz returned %d\n", err);
		return;
	}
	clockevents_register_device(&timer_clockevent);
}

void read_persistent_clock64(struct timespec64 *ts)
{
	long long nsecs;

	if (time_travel_start_set)
		nsecs = time_travel_start + time_travel_time;
	else
		nsecs = os_persistent_clock_emulation();

	set_normalized_timespec64(ts, nsecs / NSEC_PER_SEC,
				  nsecs % NSEC_PER_SEC);
}

void __init time_init(void)
{
	timer_set_signal_handler();
	late_time_init = um_timer_setup;
}

#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
unsigned long calibrate_delay_is_known(void)
{
	if (time_travel_mode == TT_MODE_INFCPU)
		return 1;
	return 0;
}

int setup_time_travel(char *str)
{
	if (strcmp(str, "=inf-cpu") == 0) {
		time_travel_mode = TT_MODE_INFCPU;
		timer_clockevent.name = "time-travel-timer-infcpu";
		timer_clocksource.name = "time-travel-clock";
		return 1;
	}

	if (!*str) {
		time_travel_mode = TT_MODE_BASIC;
		timer_clockevent.name = "time-travel-timer";
		timer_clocksource.name = "time-travel-clock";
		return 1;
	}

	return -EINVAL;
}

__setup("time-travel", setup_time_travel);
__uml_help(setup_time_travel,
"time-travel\n"
"This option just enables basic time travel mode, in which the clock/timers\n"
"inside the UML instance skip forward when there's nothing to do, rather than\n"
"waiting for real time to elapse. However, instance CPU speed is limited by\n"
"the real CPU speed, so e.g. a 10ms timer will always fire after ~10ms wall\n"
"clock (but quicker when there's nothing to do).\n"
"\n"
"time-travel=inf-cpu\n"
"This enables time travel mode with infinite processing power, in which there\n"
"are no wall clock timers, and any CPU processing happens - as seen from the\n"
"guest - instantly. This can be useful for accurate simulation regardless of\n"
"debug overhead, physical CPU speed, etc. but is somewhat dangerous as it can\n"
"easily lead to getting stuck (e.g. if anything in the system busy loops).\n");

int setup_time_travel_start(char *str)
{
	int err;

	err = kstrtoull(str, 0, &time_travel_start);
	if (err)
		return err;

	time_travel_start_set = 1;
	return 1;
}

__setup("time-travel-start", setup_time_travel_start);
__uml_help(setup_time_travel_start,
"time-travel-start=<seconds>\n"
"Configure the UML instance's wall clock to start at this value rather than\n"
"the host's wall clock at the time of UML boot.\n");
#endif