// SPDX-License-Identifier: GPL-2.0-only
/*
 * drivers/clocksource/arm_global_timer.c
 *
 * Copyright (C) 2013 STMicroelectronics (R&D) Limited.
 * Author: Stuart Menefy <stuart.menefy@st.com>
 * Author: Srinivas Kandagatla <srinivas.kandagatla@st.com>
 */

#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/clocksource.h>
#include <linux/clockchips.h>
#include <linux/cpu.h>
#include <linux/clk.h>
#include <linux/delay.h>
#include <linux/err.h>
#include <linux/io.h>
#include <linux/of.h>
#include <linux/of_irq.h>
#include <linux/of_address.h>
#include <linux/sched_clock.h>

#include <asm/cputype.h>

#define GT_COUNTER0     0x00
#define GT_COUNTER1     0x04

#define GT_CONTROL      0x08
#define GT_CONTROL_TIMER_ENABLE         BIT(0)  /* this bit is NOT banked */
#define GT_CONTROL_COMP_ENABLE          BIT(1)  /* banked */
#define GT_CONTROL_IRQ_ENABLE           BIT(2)  /* banked */
#define GT_CONTROL_AUTO_INC             BIT(3)  /* banked */
#define GT_CONTROL_PRESCALER_SHIFT      8
#define GT_CONTROL_PRESCALER_MAX        0xF
#define GT_CONTROL_PRESCALER_MASK       (GT_CONTROL_PRESCALER_MAX << \
                                         GT_CONTROL_PRESCALER_SHIFT)

#define GT_INT_STATUS   0x0c
#define GT_INT_STATUS_EVENT_FLAG        BIT(0)

#define GT_COMP0        0x10
#define GT_COMP1        0x14
#define GT_AUTO_INC     0x18

#define MAX_F_ERR 50
/*
 * We are expecting to be clocked by the ARM peripheral clock.
 *
 * Note: it is assumed we are using a prescaler value of zero, so this is
 * the units for all operations.
 */
static void __iomem *gt_base;
static struct notifier_block gt_clk_rate_change_nb;
static u32 gt_psv_new, gt_psv_bck, gt_target_rate;
static int gt_ppi;
static struct clock_event_device __percpu *gt_evt;

/*
 * To get the value from the Global Timer Counter register proceed as follows:
 * 1. Read the upper 32-bit timer counter register
 * 2. Read the lower 32-bit timer counter register
 * 3. Read the upper 32-bit timer counter register again. If the value is
 *  different to the 32-bit upper value read previously, go back to step 2.
 *  Otherwise the 64-bit timer counter value is correct.
 */
static u64 notrace _gt_counter_read(void)
{
        u64 counter;
        u32 lower;
        u32 upper, old_upper;

        upper = readl_relaxed(gt_base + GT_COUNTER1);
        do {
                old_upper = upper;
                lower = readl_relaxed(gt_base + GT_COUNTER0);
                upper = readl_relaxed(gt_base + GT_COUNTER1);
        } while (upper != old_upper);

        counter = upper;
        counter <<= 32;
        counter |= lower;
        return counter;
}

static u64 gt_counter_read(void)
{
        return _gt_counter_read();
}

/**
 * To ensure that updates to comparator value register do not set the
 * Interrupt Status Register proceed as follows:
 * 1. Clear the Comp Enable bit in the Timer Control Register.
 * 2. Write the lower 32-bit Comparator Value Register.
 * 3. Write the upper 32-bit Comparator Value Register.
 * 4. Set the Comp Enable bit and, if necessary, the IRQ enable bit.
 */
static void gt_compare_set(unsigned long delta, int periodic)
{
        u64 counter = gt_counter_read();
        unsigned long ctrl;

        counter += delta;
        ctrl = readl(gt_base + GT_CONTROL);
        ctrl &= ~(GT_CONTROL_COMP_ENABLE | GT_CONTROL_IRQ_ENABLE |
                  GT_CONTROL_AUTO_INC);
        ctrl |= GT_CONTROL_TIMER_ENABLE;
        writel_relaxed(ctrl, gt_base + GT_CONTROL);
        writel_relaxed(lower_32_bits(counter), gt_base + GT_COMP0);
        writel_relaxed(upper_32_bits(counter), gt_base + GT_COMP1);

        if (periodic) {
                writel_relaxed(delta, gt_base + GT_AUTO_INC);
                ctrl |= GT_CONTROL_AUTO_INC;
        }

        ctrl |= GT_CONTROL_COMP_ENABLE | GT_CONTROL_IRQ_ENABLE;
        writel_relaxed(ctrl, gt_base + GT_CONTROL);
}

static int gt_clockevent_shutdown(struct clock_event_device *evt)
{
        unsigned long ctrl;

        ctrl = readl(gt_base + GT_CONTROL);
        ctrl &= ~(GT_CONTROL_COMP_ENABLE | GT_CONTROL_IRQ_ENABLE |
                  GT_CONTROL_AUTO_INC);
        writel(ctrl, gt_base + GT_CONTROL);
        return 0;
}

static int gt_clockevent_set_periodic(struct clock_event_device *evt)
{
        gt_compare_set(DIV_ROUND_CLOSEST(gt_target_rate, HZ), 1);
        return 0;
}

static int gt_clockevent_set_next_event(unsigned long evt,
                                        struct clock_event_device *unused)
{
        gt_compare_set(evt, 0);
        return 0;
}

static irqreturn_t gt_clockevent_interrupt(int irq, void *dev_id)
{
        struct clock_event_device *evt = dev_id;

        if (!(readl_relaxed(gt_base + GT_INT_STATUS) &
                                GT_INT_STATUS_EVENT_FLAG))
                return IRQ_NONE;

        /**
         * ERRATA 740657( Global Timer can send 2 interrupts for
         * the same event in single-shot mode)
         * Workaround:
         *      Either disable single-shot mode.
         *      Or
         *      Modify the Interrupt Handler to avoid the
         *      offending sequence. This is achieved by clearing
         *      the Global Timer flag _after_ having incremented
         *      the Comparator register value to a higher value.
         */
        if (clockevent_state_oneshot(evt))
                gt_compare_set(ULONG_MAX, 0);

        writel_relaxed(GT_INT_STATUS_EVENT_FLAG, gt_base + GT_INT_STATUS);
        evt->event_handler(evt);

        return IRQ_HANDLED;
}

static int gt_starting_cpu(unsigned int cpu)
{
        struct clock_event_device *clk = this_cpu_ptr(gt_evt);

        clk->name = "arm_global_timer";
        clk->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT |
                CLOCK_EVT_FEAT_PERCPU;
        clk->set_state_shutdown = gt_clockevent_shutdown;
        clk->set_state_periodic = gt_clockevent_set_periodic;
        clk->set_state_oneshot = gt_clockevent_shutdown;
        clk->set_state_oneshot_stopped = gt_clockevent_shutdown;
        clk->set_next_event = gt_clockevent_set_next_event;
        clk->cpumask = cpumask_of(cpu);
        clk->rating = 300;
        clk->irq = gt_ppi;
        clockevents_config_and_register(clk, gt_target_rate,
                                        1, 0xffffffff);
        enable_percpu_irq(clk->irq, IRQ_TYPE_NONE);
        return 0;
}

static int gt_dying_cpu(unsigned int cpu)
{
        struct clock_event_device *clk = this_cpu_ptr(gt_evt);

        gt_clockevent_shutdown(clk);
        disable_percpu_irq(clk->irq);
        return 0;
}

static u64 gt_clocksource_read(struct clocksource *cs)
{
        return gt_counter_read();
}

static void gt_resume(struct clocksource *cs)
{
        unsigned long ctrl;

        ctrl = readl(gt_base + GT_CONTROL);
        if (!(ctrl & GT_CONTROL_TIMER_ENABLE))
                /* re-enable timer on resume */
                writel(GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);
}

static struct clocksource gt_clocksource = {
        .name   = "arm_global_timer",
        .rating = 300,
        .read   = gt_clocksource_read,
        .mask   = CLOCKSOURCE_MASK(64),
        .flags  = CLOCK_SOURCE_IS_CONTINUOUS,
        .resume = gt_resume,
};

#ifdef CONFIG_CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCK
static u64 notrace gt_sched_clock_read(void)
{
        return _gt_counter_read();
}
#endif

static unsigned long gt_read_long(void)
{
        return readl_relaxed(gt_base + GT_COUNTER0);
}

static struct delay_timer gt_delay_timer = {
        .read_current_timer = gt_read_long,
};

static void gt_write_presc(u32 psv)
{
        u32 reg;

        reg = readl(gt_base + GT_CONTROL);
        reg &= ~GT_CONTROL_PRESCALER_MASK;
        reg |= psv << GT_CONTROL_PRESCALER_SHIFT;
        writel(reg, gt_base + GT_CONTROL);
}

static u32 gt_read_presc(void)
{
        u32 reg;

        reg = readl(gt_base + GT_CONTROL);
        reg &= GT_CONTROL_PRESCALER_MASK;
        return reg >> GT_CONTROL_PRESCALER_SHIFT;
}

static void __init gt_delay_timer_init(void)
{
        gt_delay_timer.freq = gt_target_rate;
        register_current_timer_delay(&gt_delay_timer);
}

static int __init gt_clocksource_init(void)
{
        writel(0, gt_base + GT_CONTROL);
        writel(0, gt_base + GT_COUNTER0);
        writel(0, gt_base + GT_COUNTER1);
        /* set prescaler and enable timer on all the cores */
        writel(((CONFIG_ARM_GT_INITIAL_PRESCALER_VAL - 1) <<
                GT_CONTROL_PRESCALER_SHIFT)
               | GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);

#ifdef CONFIG_CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCK
        sched_clock_register(gt_sched_clock_read, 64, gt_target_rate);
#endif
        return clocksource_register_hz(&gt_clocksource, gt_target_rate);
}

static int gt_clk_rate_change_cb(struct notifier_block *nb,
                                 unsigned long event, void *data)
{
        struct clk_notifier_data *ndata = data;

        switch (event) {
        case PRE_RATE_CHANGE:
        {
                int psv;

                psv = DIV_ROUND_CLOSEST(ndata->new_rate,
                                        gt_target_rate);

                if (abs(gt_target_rate - (ndata->new_rate / psv)) > MAX_F_ERR)
                        return NOTIFY_BAD;

                psv--;

                /* prescaler within legal range? */
                if (psv < 0 || psv > GT_CONTROL_PRESCALER_MAX)
                        return NOTIFY_BAD;

                /*
                 * store timer clock ctrl register so we can restore it in case
                 * of an abort.
                 */
                gt_psv_bck = gt_read_presc();
                gt_psv_new = psv;
                /* scale down: adjust divider in post-change notification */
                if (ndata->new_rate < ndata->old_rate)
                        return NOTIFY_DONE;

                /* scale up: adjust divider now - before frequency change */
                gt_write_presc(psv);
                break;
        }
        case POST_RATE_CHANGE:
                /* scale up: pre-change notification did the adjustment */
                if (ndata->new_rate > ndata->old_rate)
                        return NOTIFY_OK;

                /* scale down: adjust divider now - after frequency change */
                gt_write_presc(gt_psv_new);
                break;

        case ABORT_RATE_CHANGE:
                /* we have to undo the adjustment in case we scale up */
                if (ndata->new_rate < ndata->old_rate)
                        return NOTIFY_OK;

                /* restore original register value */
                gt_write_presc(gt_psv_bck);
                break;
        default:
                return NOTIFY_DONE;
        }

        return NOTIFY_DONE;
}

static int __init global_timer_of_register(struct device_node *np)
{
        struct clk *gt_clk;
        static unsigned long gt_clk_rate;
        int err = 0;

        /*
         * In A9 r2p0 the comparators for each processor with the global timer
         * fire when the timer value is greater than or equal to. In previous
         * revisions the comparators fired when the timer value was equal to.
         */
        if (read_cpuid_part() == ARM_CPU_PART_CORTEX_A9
            && (read_cpuid_id() & 0xf0000f) < 0x200000) {
                pr_warn("global-timer: non support for this cpu version.\n");
                return -ENOSYS;
        }

        gt_ppi = irq_of_parse_and_map(np, 0);
        if (!gt_ppi) {
                pr_warn("global-timer: unable to parse irq\n");
                return -EINVAL;
        }

        gt_base = of_iomap(np, 0);
        if (!gt_base) {
                pr_warn("global-timer: invalid base address\n");
                return -ENXIO;
        }

        gt_clk = of_clk_get(np, 0);
        if (!IS_ERR(gt_clk)) {
                err = clk_prepare_enable(gt_clk);
                if (err)
                        goto out_unmap;
        } else {
                pr_warn("global-timer: clk not found\n");
                err = -EINVAL;
                goto out_unmap;
        }

        gt_clk_rate = clk_get_rate(gt_clk);
        gt_target_rate = gt_clk_rate / CONFIG_ARM_GT_INITIAL_PRESCALER_VAL;
        gt_clk_rate_change_nb.notifier_call =
                gt_clk_rate_change_cb;
        err = clk_notifier_register(gt_clk, &gt_clk_rate_change_nb);
        if (err) {
                pr_warn("Unable to register clock notifier\n");
                goto out_clk;
        }

        gt_evt = alloc_percpu(struct clock_event_device);
        if (!gt_evt) {
                pr_warn("global-timer: can't allocate memory\n");
                err = -ENOMEM;
                goto out_clk_nb;
        }

        err = request_percpu_irq(gt_ppi, gt_clockevent_interrupt,
                                 "gt", gt_evt);
        if (err) {
                pr_warn("global-timer: can't register interrupt %d (%d)\n",
                        gt_ppi, err);
                goto out_free;
        }

        /* Register and immediately configure the timer on the boot CPU */
        err = gt_clocksource_init();
        if (err)
                goto out_irq;
        
        err = cpuhp_setup_state(CPUHP_AP_ARM_GLOBAL_TIMER_STARTING,
                                "clockevents/arm/global_timer:starting",
                                gt_starting_cpu, gt_dying_cpu);
        if (err)
                goto out_irq;

        gt_delay_timer_init();

        return 0;

out_irq:
        free_percpu_irq(gt_ppi, gt_evt);
out_free:
        free_percpu(gt_evt);
out_clk_nb:
        clk_notifier_unregister(gt_clk, &gt_clk_rate_change_nb);
out_clk:
        clk_disable_unprepare(gt_clk);
out_unmap:
        iounmap(gt_base);
        WARN(err, "ARM Global timer register failed (%d)\n", err);

        return err;
}

/* Only tested on r2p2 and r3p0  */
TIMER_OF_DECLARE(arm_gt, "arm,cortex-a9-global-timer",
                        global_timer_of_register);