/*
 * Virtual PTP 1588 clock for use with KVM guests
 *
 * Copyright (C) 2017 Red Hat Inc.
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  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/device.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <uapi/linux/kvm_para.h>
#include <asm/kvm_para.h>
#include <asm/pvclock.h>
#include <asm/kvmclock.h>
#include <uapi/asm/kvm_para.h>

#include <linux/ptp_clock_kernel.h>

struct kvm_ptp_clock {
	struct ptp_clock *ptp_clock;
	struct ptp_clock_info caps;
};

DEFINE_SPINLOCK(kvm_ptp_lock);

static struct pvclock_vsyscall_time_info *hv_clock;

static struct kvm_clock_pairing clock_pair;
static phys_addr_t clock_pair_gpa;

static int ptp_kvm_get_time_fn(ktime_t *device_time,
			       struct system_counterval_t *system_counter,
			       void *ctx)
{
	unsigned long ret;
	struct timespec64 tspec;
	unsigned version;
	int cpu;
	struct pvclock_vcpu_time_info *src;

	spin_lock(&kvm_ptp_lock);

	preempt_disable_notrace();
	cpu = smp_processor_id();
	src = &hv_clock[cpu].pvti;

	do {
		/*
		 * We are using a TSC value read in the hosts
		 * kvm_hc_clock_pairing handling.
		 * So any changes to tsc_to_system_mul
		 * and tsc_shift or any other pvclock
		 * data invalidate that measurement.
		 */
		version = pvclock_read_begin(src);

		ret = kvm_hypercall2(KVM_HC_CLOCK_PAIRING,
				     clock_pair_gpa,
				     KVM_CLOCK_PAIRING_WALLCLOCK);
		if (ret != 0) {
			pr_err_ratelimited("clock pairing hypercall ret %lu\n", ret);
			spin_unlock(&kvm_ptp_lock);
			preempt_enable_notrace();
			return -EOPNOTSUPP;
		}

		tspec.tv_sec = clock_pair.sec;
		tspec.tv_nsec = clock_pair.nsec;
		ret = __pvclock_read_cycles(src, clock_pair.tsc);
	} while (pvclock_read_retry(src, version));

	preempt_enable_notrace();

	system_counter->cycles = ret;
	system_counter->cs = &kvm_clock;

	*device_time = timespec64_to_ktime(tspec);

	spin_unlock(&kvm_ptp_lock);

	return 0;
}

static int ptp_kvm_getcrosststamp(struct ptp_clock_info *ptp,
				  struct system_device_crosststamp *xtstamp)
{
	return get_device_system_crosststamp(ptp_kvm_get_time_fn, NULL,
					     NULL, xtstamp);
}

/*
 * PTP clock operations
 */

static int ptp_kvm_adjfreq(struct ptp_clock_info *ptp, s32 ppb)
{
	return -EOPNOTSUPP;
}

static int ptp_kvm_adjtime(struct ptp_clock_info *ptp, s64 delta)
{
	return -EOPNOTSUPP;
}

static int ptp_kvm_settime(struct ptp_clock_info *ptp,
			   const struct timespec64 *ts)
{
	return -EOPNOTSUPP;
}

static int ptp_kvm_gettime(struct ptp_clock_info *ptp, struct timespec64 *ts)
{
	unsigned long ret;
	struct timespec64 tspec;

	spin_lock(&kvm_ptp_lock);

	ret = kvm_hypercall2(KVM_HC_CLOCK_PAIRING,
			     clock_pair_gpa,
			     KVM_CLOCK_PAIRING_WALLCLOCK);
	if (ret != 0) {
		pr_err_ratelimited("clock offset hypercall ret %lu\n", ret);
		spin_unlock(&kvm_ptp_lock);
		return -EOPNOTSUPP;
	}

	tspec.tv_sec = clock_pair.sec;
	tspec.tv_nsec = clock_pair.nsec;
	spin_unlock(&kvm_ptp_lock);

	memcpy(ts, &tspec, sizeof(struct timespec64));

	return 0;
}

static int ptp_kvm_enable(struct ptp_clock_info *ptp,
			  struct ptp_clock_request *rq, int on)
{
	return -EOPNOTSUPP;
}

static const struct ptp_clock_info ptp_kvm_caps = {
	.owner		= THIS_MODULE,
	.name		= "KVM virtual PTP",
	.max_adj	= 0,
	.n_ext_ts	= 0,
	.n_pins		= 0,
	.pps		= 0,
	.adjfreq	= ptp_kvm_adjfreq,
	.adjtime	= ptp_kvm_adjtime,
	.gettime64	= ptp_kvm_gettime,
	.settime64	= ptp_kvm_settime,
	.enable		= ptp_kvm_enable,
	.getcrosststamp = ptp_kvm_getcrosststamp,
};

/* module operations */

static struct kvm_ptp_clock kvm_ptp_clock;

static void __exit ptp_kvm_exit(void)
{
	ptp_clock_unregister(kvm_ptp_clock.ptp_clock);
}

static int __init ptp_kvm_init(void)
{
	long ret;

	if (!kvm_para_available())
		return -ENODEV;

	clock_pair_gpa = slow_virt_to_phys(&clock_pair);
	hv_clock = pvclock_get_pvti_cpu0_va();

	if (!hv_clock)
		return -ENODEV;

	ret = kvm_hypercall2(KVM_HC_CLOCK_PAIRING, clock_pair_gpa,
			KVM_CLOCK_PAIRING_WALLCLOCK);
	if (ret == -KVM_ENOSYS || ret == -KVM_EOPNOTSUPP)
		return -ENODEV;

	kvm_ptp_clock.caps = ptp_kvm_caps;

	kvm_ptp_clock.ptp_clock = ptp_clock_register(&kvm_ptp_clock.caps, NULL);

	return PTR_ERR_OR_ZERO(kvm_ptp_clock.ptp_clock);
}

module_init(ptp_kvm_init);
module_exit(ptp_kvm_exit);

MODULE_AUTHOR("Marcelo Tosatti <mtosatti@redhat.com>");
MODULE_DESCRIPTION("PTP clock using KVMCLOCK");
MODULE_LICENSE("GPL");