/* Copyright (c) 2011 The Regents of the University of California
 * Copyright (c) 2018 Google Inc.
 * Barret Rhoden <brho@cs.berkeley.edu>
 * See LICENSE for details.
 *
 * Alarms.  This includes various ways to sleep for a while or defer work on a
 * specific timer.  These can be per-core, global or whatever.  Deferred work
 * is a function pointer which runs in interrupt context when the alarm goes off
 * (picture running the ksched then).
 *
 * Like with most systems, you won't wake up til after the time you specify (for
 * now).  This might change, esp if we tweak things to coalesce alarms.
 *
 * All tchains come with locks.  Originally, I left these out, since the pcpu
 * tchains didn't need them (disable_irq was sufficient).  However, disabling
 * alarms remotely (a valid use case) is a real pain without locks, so now
 * everyone has locks.  As an added benefit, you can submit an alarm to another
 * core's pcpu tchain (though it probably costs an extra IRQ).  Note there is a
 * lock ordering, tchains before awaiters (when they are grabbed together).
 *
 * There are two options for pcpu alarms: hard IRQ and routine KMSG (RKM).
 * IRQ alarms are run directly in the timer interrupt handler and take a hw_tf
 * parameter in addition to the standard alarm_waiter.  RKM alarms are executed
 * when kernel messages are executed, which is out of IRQ context.  RKMs are
 * safer, since you can sleep (qlock, some kmalloc, etc) and you do not need
 * irqsave locks.
 *
 * Another important difference between IRQ and RKM alarms comes when cancelling
 * or unsetting an alarm.  When you cancel (unset or reset) an alarm, you may
 * need to block until the RKM has run.  IRQ alarms run with the tchain lock
 * held, so once the canceller grabs the lock, it has either run already or will
 * not at all.  With RKMs, the handler runs outside of the lock.  Thus you may
 * have to wait until the RKM has run, and the RKM might be waiting to run on
 * your core.
 *
 * Note that RKM unset_alarm() has a waits-on dependency with the actual alarm
 * handler, so be careful of deadlock.
 *
 * Quick howto, using the pcpu tchains:
 * 	struct timer_chain *tchain = &per_cpu_info[core_id()].tchain;
 * To block your kthread on an alarm:
 * 	struct alarm_waiter *waiter = kmalloc(sizeof(struct alarm_waiter), 0);
 *
 * 	init_awaiter(waiter, HANDLER);
 * 	set_awaiter_rel(waiter, USEC);
 * 	set_alarm(tchain, waiter);
 *
 * If you want the HANDLER to run again, do this at the end of it:
 * 	set_awaiter_rel(waiter, USEC);	// or whenever you want it to fire
 * 	set_alarm(tchain, waiter);
 * or:
 * 	reset_alarm_rel(tchain, waiter, USEC);
 *
 * Don't forget to manage your memory at some (safe) point:
 * 	kfree(waiter);
 * In the future, we might have a slab for these.  You can get it from wherever
 * you want, just be careful if you use the stack. */

#pragma once

#include <ros/common.h>
#include <sys/queue.h>
#include <kthread.h>

/* These structures allow code to defer work for a certain amount of time.
 * Timer chains (like off a per-core timer) are made of lists/trees of these. */
struct alarm_waiter {
	uint64_t 			wake_up_time;
	void (*func) (struct alarm_waiter *waiter);
	void				*data;
	TAILQ_ENTRY(alarm_waiter)	next;
	bool				on_tchain;
};
TAILQ_HEAD(awaiters_tailq, alarm_waiter);		/* ideally not a LL */

typedef void (*alarm_handler)(struct alarm_waiter *waiter);

/* One of these per alarm source, such as a per-core timer.  All tchains come
 * with a lock, even if its rarely needed (like the pcpu tchains).
 * set_interrupt() is a method for setting the interrupt source. */
struct timer_chain {
	spinlock_t			lock;
	struct awaiters_tailq		waiters;
	struct alarm_waiter		*running;
	uint64_t			earliest_time;
	uint64_t			latest_time;
	struct cond_var			cv;
	void (*set_interrupt)(struct timer_chain *);
};

/* Called once per timer chain, currently in per_cpu_init() */
void init_timer_chain(struct timer_chain *tchain,
                      void (*set_interrupt)(struct timer_chain *));
/* For fresh alarm waiters.  func == 0 for kthreads */
void init_awaiter(struct alarm_waiter *waiter,
                  void (*func) (struct alarm_waiter *));
/* Sets the time an awaiter goes off */
void set_awaiter_abs(struct alarm_waiter *waiter, uint64_t abs_time);
void set_awaiter_rel(struct alarm_waiter *waiter, uint64_t usleep);
void set_awaiter_inc(struct alarm_waiter *waiter, uint64_t usleep);
/* Arms/disarms the alarm.  Can be called from within a handler.*/
void set_alarm(struct timer_chain *tchain, struct alarm_waiter *waiter);
/* Unset and reset may block if the alarm is not IRQ.  Do not call from within a
 * handler.  Returns TRUE if you stopped the alarm from firing. */
bool unset_alarm(struct timer_chain *tchain, struct alarm_waiter *waiter);
/* Convenience wrappers for unset, then set.  Slower, but easier than just
 * setting, since you don't need to know if it fired.  Returns TRUE if the alarm
 * did not fire before your reset. */
bool reset_alarm_abs(struct timer_chain *tchain, struct alarm_waiter *waiter,
                     uint64_t abs_time);
bool reset_alarm_rel(struct timer_chain *tchain, struct alarm_waiter *waiter,
                     uint64_t usleep);

/* Interrupt handlers need to call this.  Don't call it directly. */
void __trigger_tchain(struct timer_chain *tchain, struct hw_trapframe *hw_tf);
/* Sets the timer chain interrupt according to the next timer in the chain. */
void set_pcpu_alarm_interrupt(struct timer_chain *tchain);

static inline bool alarm_expired(struct alarm_waiter *awaiter)
{
	return awaiter->wake_up_time <= read_tsc();
}

/* Debugging */
#define ALARM_POISON_TIME 12345		/* could use some work */
void print_chain(struct timer_chain *tchain);
void print_pcpu_chains(void);