// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) 2023 Ventana Micro Systems Inc.
 */

#define pr_fmt(fmt) "riscv-pv: " fmt

#include <linux/cpuhotplug.h>
#include <linux/compiler.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/jump_label.h>
#include <linux/kconfig.h>
#include <linux/kernel.h>
#include <linux/percpu-defs.h>
#include <linux/printk.h>
#include <linux/static_call.h>
#include <linux/types.h>
#include <linux/sched/cputime.h>

#include <asm/barrier.h>
#include <asm/page.h>
#include <asm/paravirt.h>
#include <asm/sbi.h>

static bool steal_acc = true;
static int __init parse_no_stealacc(char *arg)
{
        steal_acc = false;
        return 0;
}

early_param("no-steal-acc", parse_no_stealacc);

static DEFINE_PER_CPU(struct sbi_sta_struct, steal_time) __aligned(64);

static bool __init has_pv_steal_clock(void)
{
        if (sbi_spec_version >= sbi_mk_version(2, 0) &&
            sbi_probe_extension(SBI_EXT_STA) > 0) {
                pr_info("SBI STA extension detected\n");
                return true;
        }

        return false;
}

static int sbi_sta_steal_time_set_shmem(unsigned long lo, unsigned long hi,
                                        unsigned long flags)
{
        struct sbiret ret;

        ret = sbi_ecall(SBI_EXT_STA, SBI_EXT_STA_STEAL_TIME_SET_SHMEM,
                        lo, hi, flags, 0, 0, 0);
        if (ret.error) {
                if (lo == SBI_SHMEM_DISABLE && hi == SBI_SHMEM_DISABLE)
                        pr_warn("Failed to disable steal-time shmem");
                else
                        pr_warn("Failed to set steal-time shmem");
                return sbi_err_map_linux_errno(ret.error);
        }

        return 0;
}

static int pv_time_cpu_online(unsigned int cpu)
{
        struct sbi_sta_struct *st = this_cpu_ptr(&steal_time);
        phys_addr_t pa = __pa(st);
        unsigned long lo = (unsigned long)pa;
        unsigned long hi = IS_ENABLED(CONFIG_32BIT) ? upper_32_bits((u64)pa) : 0;

        return sbi_sta_steal_time_set_shmem(lo, hi, 0);
}

static int pv_time_cpu_down_prepare(unsigned int cpu)
{
        return sbi_sta_steal_time_set_shmem(SBI_SHMEM_DISABLE,
                                            SBI_SHMEM_DISABLE, 0);
}

static u64 pv_time_steal_clock(int cpu)
{
        struct sbi_sta_struct *st = per_cpu_ptr(&steal_time, cpu);
        __le32 sequence;
        __le64 steal;

        /*
         * Check the sequence field before and after reading the steal
         * field. Repeat the read if it is different or odd.
         */
        do {
                sequence = READ_ONCE(st->sequence);
                virt_rmb();
                steal = READ_ONCE(st->steal);
                virt_rmb();
        } while ((le32_to_cpu(sequence) & 1) ||
                 sequence != READ_ONCE(st->sequence));

        return le64_to_cpu(steal);
}

int __init pv_time_init(void)
{
        int ret;

        if (!has_pv_steal_clock())
                return 0;

        ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
                                "riscv/pv_time:online",
                                pv_time_cpu_online,
                                pv_time_cpu_down_prepare);
        if (ret < 0)
                return ret;

        static_call_update(pv_steal_clock, pv_time_steal_clock);

        static_key_slow_inc(&paravirt_steal_enabled);
        if (steal_acc)
                static_key_slow_inc(&paravirt_steal_rq_enabled);

        pr_info("Computing paravirt steal-time\n");

        return 0;
}