// SPDX-License-Identifier: GPL-2.0
#include <linux/init.h>
#include <linux/pci.h>
#include <linux/percpu.h>
#include <linux/delay.h>
#include <linux/spinlock.h>
#include <linux/interrupt.h>

#include <asm/hpet.h>
#include <asm/time.h>

#define SMBUS_CFG_BASE          (loongson_sysconf.ht_control_base + 0x0300a000)
#define SMBUS_PCI_REG40         0x40
#define SMBUS_PCI_REG64         0x64
#define SMBUS_PCI_REGB4         0xb4

#define HPET_MIN_CYCLES         16
#define HPET_MIN_PROG_DELTA     (HPET_MIN_CYCLES * 12)

static DEFINE_SPINLOCK(hpet_lock);
DEFINE_PER_CPU(struct clock_event_device, hpet_clockevent_device);

static unsigned int smbus_read(int offset)
{
        return *(volatile unsigned int *)(SMBUS_CFG_BASE + offset);
}

static void smbus_write(int offset, int data)
{
        *(volatile unsigned int *)(SMBUS_CFG_BASE + offset) = data;
}

static void smbus_enable(int offset, int bit)
{
        unsigned int cfg = smbus_read(offset);

        cfg |= bit;
        smbus_write(offset, cfg);
}

static int hpet_read(int offset)
{
        return *(volatile unsigned int *)(HPET_MMIO_ADDR + offset);
}

static void hpet_write(int offset, int data)
{
        *(volatile unsigned int *)(HPET_MMIO_ADDR + offset) = data;
}

static void hpet_start_counter(void)
{
        unsigned int cfg = hpet_read(HPET_CFG);

        cfg |= HPET_CFG_ENABLE;
        hpet_write(HPET_CFG, cfg);
}

static void hpet_stop_counter(void)
{
        unsigned int cfg = hpet_read(HPET_CFG);

        cfg &= ~HPET_CFG_ENABLE;
        hpet_write(HPET_CFG, cfg);
}

static void hpet_reset_counter(void)
{
        hpet_write(HPET_COUNTER, 0);
        hpet_write(HPET_COUNTER + 4, 0);
}

static void hpet_restart_counter(void)
{
        hpet_stop_counter();
        hpet_reset_counter();
        hpet_start_counter();
}

static void hpet_enable_legacy_int(void)
{
        /* Do nothing on Loongson-3 */
}

static int hpet_set_state_periodic(struct clock_event_device *evt)
{
        int cfg;

        spin_lock(&hpet_lock);

        pr_info("set clock event to periodic mode!\n");
        /* stop counter */
        hpet_stop_counter();

        /* enables the timer0 to generate a periodic interrupt */
        cfg = hpet_read(HPET_T0_CFG);
        cfg &= ~HPET_TN_LEVEL;
        cfg |= HPET_TN_ENABLE | HPET_TN_PERIODIC | HPET_TN_SETVAL |
                HPET_TN_32BIT;
        hpet_write(HPET_T0_CFG, cfg);

        /* set the comparator */
        hpet_write(HPET_T0_CMP, HPET_COMPARE_VAL);
        udelay(1);
        hpet_write(HPET_T0_CMP, HPET_COMPARE_VAL);

        /* start counter */
        hpet_start_counter();

        spin_unlock(&hpet_lock);
        return 0;
}

static int hpet_set_state_shutdown(struct clock_event_device *evt)
{
        int cfg;

        spin_lock(&hpet_lock);

        cfg = hpet_read(HPET_T0_CFG);
        cfg &= ~HPET_TN_ENABLE;
        hpet_write(HPET_T0_CFG, cfg);

        spin_unlock(&hpet_lock);
        return 0;
}

static int hpet_set_state_oneshot(struct clock_event_device *evt)
{
        int cfg;

        spin_lock(&hpet_lock);

        pr_info("set clock event to one shot mode!\n");
        cfg = hpet_read(HPET_T0_CFG);
        /*
         * set timer0 type
         * 1 : periodic interrupt
         * 0 : non-periodic(oneshot) interrupt
         */
        cfg &= ~HPET_TN_PERIODIC;
        cfg |= HPET_TN_ENABLE | HPET_TN_32BIT;
        hpet_write(HPET_T0_CFG, cfg);

        spin_unlock(&hpet_lock);
        return 0;
}

static int hpet_tick_resume(struct clock_event_device *evt)
{
        spin_lock(&hpet_lock);
        hpet_enable_legacy_int();
        spin_unlock(&hpet_lock);

        return 0;
}

static int hpet_next_event(unsigned long delta,
                struct clock_event_device *evt)
{
        u32 cnt;
        s32 res;

        cnt = hpet_read(HPET_COUNTER);
        cnt += (u32) delta;
        hpet_write(HPET_T0_CMP, cnt);

        res = (s32)(cnt - hpet_read(HPET_COUNTER));

        return res < HPET_MIN_CYCLES ? -ETIME : 0;
}

static irqreturn_t hpet_irq_handler(int irq, void *data)
{
        int is_irq;
        struct clock_event_device *cd;
        unsigned int cpu = smp_processor_id();

        is_irq = hpet_read(HPET_STATUS);
        if (is_irq & HPET_T0_IRS) {
                /* clear the TIMER0 irq status register */
                hpet_write(HPET_STATUS, HPET_T0_IRS);
                cd = &per_cpu(hpet_clockevent_device, cpu);
                cd->event_handler(cd);
                return IRQ_HANDLED;
        }
        return IRQ_NONE;
}

/*
 * hpet address assignation and irq setting should be done in bios.
 * but pmon don't do this, we just setup here directly.
 * The operation under is normal. unfortunately, hpet_setup process
 * is before pci initialize.
 *
 * {
 *      struct pci_dev *pdev;
 *
 *      pdev = pci_get_device(PCI_VENDOR_ID_ATI, PCI_DEVICE_ID_ATI_SBX00_SMBUS, NULL);
 *      pci_write_config_word(pdev, SMBUS_PCI_REGB4, HPET_ADDR);
 *
 *      ...
 * }
 */
static void hpet_setup(void)
{
        /* set hpet base address */
        smbus_write(SMBUS_PCI_REGB4, HPET_ADDR);

        /* enable decoding of access to HPET MMIO*/
        smbus_enable(SMBUS_PCI_REG40, (1 << 28));

        /* HPET irq enable */
        smbus_enable(SMBUS_PCI_REG64, (1 << 10));

        hpet_enable_legacy_int();
}

void __init setup_hpet_timer(void)
{
        unsigned long flags = IRQF_NOBALANCING | IRQF_TIMER;
        unsigned int cpu = smp_processor_id();
        struct clock_event_device *cd;

        hpet_setup();

        cd = &per_cpu(hpet_clockevent_device, cpu);
        cd->name = "hpet";
        cd->rating = 100;
        cd->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT;
        cd->set_state_shutdown = hpet_set_state_shutdown;
        cd->set_state_periodic = hpet_set_state_periodic;
        cd->set_state_oneshot = hpet_set_state_oneshot;
        cd->tick_resume = hpet_tick_resume;
        cd->set_next_event = hpet_next_event;
        cd->irq = HPET_T0_IRQ;
        cd->cpumask = cpumask_of(cpu);
        clockevent_set_clock(cd, HPET_FREQ);
        cd->max_delta_ns = clockevent_delta2ns(0x7fffffff, cd);
        cd->max_delta_ticks = 0x7fffffff;
        cd->min_delta_ns = clockevent_delta2ns(HPET_MIN_PROG_DELTA, cd);
        cd->min_delta_ticks = HPET_MIN_PROG_DELTA;

        clockevents_register_device(cd);
        if (request_irq(HPET_T0_IRQ, hpet_irq_handler, flags, "hpet", NULL))
                pr_err("Failed to request irq %d (hpet)\n", HPET_T0_IRQ);
        pr_info("hpet clock event device register\n");
}

static u64 hpet_read_counter(struct clocksource *cs)
{
        return (u64)hpet_read(HPET_COUNTER);
}

static void hpet_suspend(struct clocksource *cs)
{
}

static void hpet_resume(struct clocksource *cs)
{
        hpet_setup();
        hpet_restart_counter();
}

static struct clocksource csrc_hpet = {
        .name = "hpet",
        /* mips clocksource rating is less than 300, so hpet is better. */
        .rating = 300,
        .read = hpet_read_counter,
        .mask = CLOCKSOURCE_MASK(32),
        /* oneshot mode work normal with this flag */
        .flags = CLOCK_SOURCE_IS_CONTINUOUS,
        .suspend = hpet_suspend,
        .resume = hpet_resume,
        .mult = 0,
        .shift = 10,
};

int __init init_hpet_clocksource(void)
{
        csrc_hpet.mult = clocksource_hz2mult(HPET_FREQ, csrc_hpet.shift);
        return clocksource_register_hz(&csrc_hpet, HPET_FREQ);
}

arch_initcall(init_hpet_clocksource);