/*
 * X86 specific Hyper-V initialization code.
 *
 * Copyright (C) 2016, Microsoft, Inc.
 *
 * Author : K. Y. Srinivasan <kys@microsoft.com>
 *
 * 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, GOOD TITLE or
 * NON INFRINGEMENT.  See the GNU General Public License for more
 * details.
 *
 */

#include <linux/types.h>
#include <asm/hypervisor.h>
#include <asm/hyperv.h>
#include <asm/mshyperv.h>
#include <linux/version.h>
#include <linux/vmalloc.h>
#include <linux/mm.h>
#include <linux/clockchips.h>


#ifdef CONFIG_X86_64

static struct ms_hyperv_tsc_page *tsc_pg;

static u64 read_hv_clock_tsc(struct clocksource *arg)
{
	u64 current_tick;

	if (tsc_pg->tsc_sequence != 0) {
		/*
		 * Use the tsc page to compute the value.
		 */

		while (1) {
			u64 tmp;
			u32 sequence = tsc_pg->tsc_sequence;
			u64 cur_tsc;
			u64 scale = tsc_pg->tsc_scale;
			s64 offset = tsc_pg->tsc_offset;

			rdtscll(cur_tsc);
			/* current_tick = ((cur_tsc *scale) >> 64) + offset */
			asm("mulq %3"
				: "=d" (current_tick), "=a" (tmp)
				: "a" (cur_tsc), "r" (scale));

			current_tick += offset;
			if (tsc_pg->tsc_sequence == sequence)
				return current_tick;

			if (tsc_pg->tsc_sequence != 0)
				continue;
			/*
			 * Fallback using MSR method.
			 */
			break;
		}
	}
	rdmsrl(HV_X64_MSR_TIME_REF_COUNT, current_tick);
	return current_tick;
}

static struct clocksource hyperv_cs_tsc = {
		.name		= "hyperv_clocksource_tsc_page",
		.rating		= 400,
		.read		= read_hv_clock_tsc,
		.mask		= CLOCKSOURCE_MASK(64),
		.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
};
#endif

static u64 read_hv_clock_msr(struct clocksource *arg)
{
	u64 current_tick;
	/*
	 * Read the partition counter to get the current tick count. This count
	 * is set to 0 when the partition is created and is incremented in
	 * 100 nanosecond units.
	 */
	rdmsrl(HV_X64_MSR_TIME_REF_COUNT, current_tick);
	return current_tick;
}

static struct clocksource hyperv_cs_msr = {
	.name		= "hyperv_clocksource_msr",
	.rating		= 400,
	.read		= read_hv_clock_msr,
	.mask		= CLOCKSOURCE_MASK(64),
	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
};

static void *hypercall_pg;
/*
 * This function is to be invoked early in the boot sequence after the
 * hypervisor has been detected.
 *
 * 1. Setup the hypercall page.
 * 2. Register Hyper-V specific clocksource.
 */
void hyperv_init(void)
{
	u64 guest_id;
	union hv_x64_msr_hypercall_contents hypercall_msr;

	if (x86_hyper != &x86_hyper_ms_hyperv)
		return;

	/*
	 * Setup the hypercall page and enable hypercalls.
	 * 1. Register the guest ID
	 * 2. Enable the hypercall and register the hypercall page
	 */
	guest_id = generate_guest_id(0, LINUX_VERSION_CODE, 0);
	wrmsrl(HV_X64_MSR_GUEST_OS_ID, guest_id);

	hypercall_pg  = __vmalloc(PAGE_SIZE, GFP_KERNEL, PAGE_KERNEL_EXEC);
	if (hypercall_pg == NULL) {
		wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
		return;
	}

	rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
	hypercall_msr.enable = 1;
	hypercall_msr.guest_physical_address = vmalloc_to_pfn(hypercall_pg);
	wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);

	/*
	 * Register Hyper-V specific clocksource.
	 */
#ifdef CONFIG_X86_64
	if (ms_hyperv.features & HV_X64_MSR_REFERENCE_TSC_AVAILABLE) {
		union hv_x64_msr_hypercall_contents tsc_msr;

		tsc_pg = __vmalloc(PAGE_SIZE, GFP_KERNEL, PAGE_KERNEL);
		if (!tsc_pg) {
			clocksource_register_hz(&hyperv_cs_msr, NSEC_PER_SEC/100);
			return;
		}

		rdmsrl(HV_X64_MSR_REFERENCE_TSC, tsc_msr.as_uint64);

		tsc_msr.enable = 1;
		tsc_msr.guest_physical_address = vmalloc_to_pfn(tsc_pg);

		wrmsrl(HV_X64_MSR_REFERENCE_TSC, tsc_msr.as_uint64);
		clocksource_register_hz(&hyperv_cs_tsc, NSEC_PER_SEC/100);
		return;
	}
#endif
	/*
	 * For 32 bit guests just use the MSR based mechanism for reading
	 * the partition counter.
	 */

	if (ms_hyperv.features & HV_X64_MSR_TIME_REF_COUNT_AVAILABLE)
		clocksource_register_hz(&hyperv_cs_msr, NSEC_PER_SEC/100);
}

/*
 * hv_do_hypercall- Invoke the specified hypercall
 */
u64 hv_do_hypercall(u64 control, void *input, void *output)
{
	u64 input_address = (input) ? virt_to_phys(input) : 0;
	u64 output_address = (output) ? virt_to_phys(output) : 0;
#ifdef CONFIG_X86_64
	u64 hv_status = 0;

	if (!hypercall_pg)
		return (u64)ULLONG_MAX;

	__asm__ __volatile__("mov %0, %%r8" : : "r" (output_address) : "r8");
	__asm__ __volatile__("call *%3" : "=a" (hv_status) :
			     "c" (control), "d" (input_address),
			     "m" (hypercall_pg));

	return hv_status;

#else

	u32 control_hi = control >> 32;
	u32 control_lo = control & 0xFFFFFFFF;
	u32 hv_status_hi = 1;
	u32 hv_status_lo = 1;
	u32 input_address_hi = input_address >> 32;
	u32 input_address_lo = input_address & 0xFFFFFFFF;
	u32 output_address_hi = output_address >> 32;
	u32 output_address_lo = output_address & 0xFFFFFFFF;

	if (!hypercall_pg)
		return (u64)ULLONG_MAX;

	__asm__ __volatile__ ("call *%8" : "=d"(hv_status_hi),
			      "=a"(hv_status_lo) : "d" (control_hi),
			      "a" (control_lo), "b" (input_address_hi),
			      "c" (input_address_lo), "D"(output_address_hi),
			      "S"(output_address_lo), "m" (hypercall_pg));

	return hv_status_lo | ((u64)hv_status_hi << 32);
#endif /* !x86_64 */
}
EXPORT_SYMBOL_GPL(hv_do_hypercall);