/*
 * This file contains driver for the Cadence Triple Timer Counter Rev 06
 *
 *  Copyright (C) 2011-2013 Xilinx
 *
 * based on arch/mips/kernel/time.c timer driver
 *
 * This software is licensed under the terms of the GNU General Public
 * License version 2, as published by the Free Software Foundation, and
 * may be copied, distributed, and modified under those terms.
 *
 * 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/clk.h>
#include <linux/interrupt.h>
#include <linux/clockchips.h>
#include <linux/of_address.h>
#include <linux/of_irq.h>
#include <linux/slab.h>
#include <linux/sched_clock.h>

/*
 * This driver configures the 2 16/32-bit count-up timers as follows:
 *
 * T1: Timer 1, clocksource for generic timekeeping
 * T2: Timer 2, clockevent source for hrtimers
 * T3: Timer 3, <unused>
 *
 * The input frequency to the timer module for emulation is 2.5MHz which is
 * common to all the timer channels (T1, T2, and T3). With a pre-scaler of 32,
 * the timers are clocked at 78.125KHz (12.8 us resolution).

 * The input frequency to the timer module in silicon is configurable and
 * obtained from device tree. The pre-scaler of 32 is used.
 */

/*
 * Timer Register Offset Definitions of Timer 1, Increment base address by 4
 * and use same offsets for Timer 2
 */
#define TTC_CLK_CNTRL_OFFSET            0x00 /* Clock Control Reg, RW */
#define TTC_CNT_CNTRL_OFFSET            0x0C /* Counter Control Reg, RW */
#define TTC_COUNT_VAL_OFFSET            0x18 /* Counter Value Reg, RO */
#define TTC_INTR_VAL_OFFSET             0x24 /* Interval Count Reg, RW */
#define TTC_ISR_OFFSET          0x54 /* Interrupt Status Reg, RO */
#define TTC_IER_OFFSET          0x60 /* Interrupt Enable Reg, RW */

#define TTC_CNT_CNTRL_DISABLE_MASK      0x1

#define TTC_CLK_CNTRL_CSRC_MASK         (1 << 5)        /* clock source */
#define TTC_CLK_CNTRL_PSV_MASK          0x1e
#define TTC_CLK_CNTRL_PSV_SHIFT         1

/*
 * Setup the timers to use pre-scaling, using a fixed value for now that will
 * work across most input frequency, but it may need to be more dynamic
 */
#define PRESCALE_EXPONENT       11      /* 2 ^ PRESCALE_EXPONENT = PRESCALE */
#define PRESCALE                2048    /* The exponent must match this */
#define CLK_CNTRL_PRESCALE      ((PRESCALE_EXPONENT - 1) << 1)
#define CLK_CNTRL_PRESCALE_EN   1
#define CNT_CNTRL_RESET         (1 << 4)

#define MAX_F_ERR 50

/**
 * struct ttc_timer - This definition defines local timer structure
 *
 * @base_addr:  Base address of timer
 * @freq:       Timer input clock frequency
 * @clk:        Associated clock source
 * @clk_rate_change_nb  Notifier block for clock rate changes
 */
struct ttc_timer {
        void __iomem *base_addr;
        unsigned long freq;
        struct clk *clk;
        struct notifier_block clk_rate_change_nb;
};

#define to_ttc_timer(x) \
                container_of(x, struct ttc_timer, clk_rate_change_nb)

struct ttc_timer_clocksource {
        u32                     scale_clk_ctrl_reg_old;
        u32                     scale_clk_ctrl_reg_new;
        struct ttc_timer        ttc;
        struct clocksource      cs;
};

#define to_ttc_timer_clksrc(x) \
                container_of(x, struct ttc_timer_clocksource, cs)

struct ttc_timer_clockevent {
        struct ttc_timer                ttc;
        struct clock_event_device       ce;
};

#define to_ttc_timer_clkevent(x) \
                container_of(x, struct ttc_timer_clockevent, ce)

static void __iomem *ttc_sched_clock_val_reg;

/**
 * ttc_set_interval - Set the timer interval value
 *
 * @timer:      Pointer to the timer instance
 * @cycles:     Timer interval ticks
 **/
static void ttc_set_interval(struct ttc_timer *timer,
                                        unsigned long cycles)
{
        u32 ctrl_reg;

        /* Disable the counter, set the counter value  and re-enable counter */
        ctrl_reg = readl_relaxed(timer->base_addr + TTC_CNT_CNTRL_OFFSET);
        ctrl_reg |= TTC_CNT_CNTRL_DISABLE_MASK;
        writel_relaxed(ctrl_reg, timer->base_addr + TTC_CNT_CNTRL_OFFSET);

        writel_relaxed(cycles, timer->base_addr + TTC_INTR_VAL_OFFSET);

        /*
         * Reset the counter (0x10) so that it starts from 0, one-shot
         * mode makes this needed for timing to be right.
         */
        ctrl_reg |= CNT_CNTRL_RESET;
        ctrl_reg &= ~TTC_CNT_CNTRL_DISABLE_MASK;
        writel_relaxed(ctrl_reg, timer->base_addr + TTC_CNT_CNTRL_OFFSET);
}

/**
 * ttc_clock_event_interrupt - Clock event timer interrupt handler
 *
 * @irq:        IRQ number of the Timer
 * @dev_id:     void pointer to the ttc_timer instance
 *
 * returns: Always IRQ_HANDLED - success
 **/
static irqreturn_t ttc_clock_event_interrupt(int irq, void *dev_id)
{
        struct ttc_timer_clockevent *ttce = dev_id;
        struct ttc_timer *timer = &ttce->ttc;

        /* Acknowledge the interrupt and call event handler */
        readl_relaxed(timer->base_addr + TTC_ISR_OFFSET);

        ttce->ce.event_handler(&ttce->ce);

        return IRQ_HANDLED;
}

/**
 * __ttc_clocksource_read - Reads the timer counter register
 *
 * returns: Current timer counter register value
 **/
static cycle_t __ttc_clocksource_read(struct clocksource *cs)
{
        struct ttc_timer *timer = &to_ttc_timer_clksrc(cs)->ttc;

        return (cycle_t)readl_relaxed(timer->base_addr +
                                TTC_COUNT_VAL_OFFSET);
}

static u64 notrace ttc_sched_clock_read(void)
{
        return readl_relaxed(ttc_sched_clock_val_reg);
}

/**
 * ttc_set_next_event - Sets the time interval for next event
 *
 * @cycles:     Timer interval ticks
 * @evt:        Address of clock event instance
 *
 * returns: Always 0 - success
 **/
static int ttc_set_next_event(unsigned long cycles,
                                        struct clock_event_device *evt)
{
        struct ttc_timer_clockevent *ttce = to_ttc_timer_clkevent(evt);
        struct ttc_timer *timer = &ttce->ttc;

        ttc_set_interval(timer, cycles);
        return 0;
}

/**
 * ttc_set_{shutdown|oneshot|periodic} - Sets the state of timer
 *
 * @evt:        Address of clock event instance
 **/
static int ttc_shutdown(struct clock_event_device *evt)
{
        struct ttc_timer_clockevent *ttce = to_ttc_timer_clkevent(evt);
        struct ttc_timer *timer = &ttce->ttc;
        u32 ctrl_reg;

        ctrl_reg = readl_relaxed(timer->base_addr + TTC_CNT_CNTRL_OFFSET);
        ctrl_reg |= TTC_CNT_CNTRL_DISABLE_MASK;
        writel_relaxed(ctrl_reg, timer->base_addr + TTC_CNT_CNTRL_OFFSET);
        return 0;
}

static int ttc_set_periodic(struct clock_event_device *evt)
{
        struct ttc_timer_clockevent *ttce = to_ttc_timer_clkevent(evt);
        struct ttc_timer *timer = &ttce->ttc;

        ttc_set_interval(timer,
                         DIV_ROUND_CLOSEST(ttce->ttc.freq, PRESCALE * HZ));
        return 0;
}

static int ttc_resume(struct clock_event_device *evt)
{
        struct ttc_timer_clockevent *ttce = to_ttc_timer_clkevent(evt);
        struct ttc_timer *timer = &ttce->ttc;
        u32 ctrl_reg;

        ctrl_reg = readl_relaxed(timer->base_addr + TTC_CNT_CNTRL_OFFSET);
        ctrl_reg &= ~TTC_CNT_CNTRL_DISABLE_MASK;
        writel_relaxed(ctrl_reg, timer->base_addr + TTC_CNT_CNTRL_OFFSET);
        return 0;
}

static int ttc_rate_change_clocksource_cb(struct notifier_block *nb,
                unsigned long event, void *data)
{
        struct clk_notifier_data *ndata = data;
        struct ttc_timer *ttc = to_ttc_timer(nb);
        struct ttc_timer_clocksource *ttccs = container_of(ttc,
                        struct ttc_timer_clocksource, ttc);

        switch (event) {
        case PRE_RATE_CHANGE:
        {
                u32 psv;
                unsigned long factor, rate_low, rate_high;

                if (ndata->new_rate > ndata->old_rate) {
                        factor = DIV_ROUND_CLOSEST(ndata->new_rate,
                                        ndata->old_rate);
                        rate_low = ndata->old_rate;
                        rate_high = ndata->new_rate;
                } else {
                        factor = DIV_ROUND_CLOSEST(ndata->old_rate,
                                        ndata->new_rate);
                        rate_low = ndata->new_rate;
                        rate_high = ndata->old_rate;
                }

                if (!is_power_of_2(factor))
                                return NOTIFY_BAD;

                if (abs(rate_high - (factor * rate_low)) > MAX_F_ERR)
                        return NOTIFY_BAD;

                factor = __ilog2_u32(factor);

                /*
                 * store timer clock ctrl register so we can restore it in case
                 * of an abort.
                 */
                ttccs->scale_clk_ctrl_reg_old =
                        readl_relaxed(ttccs->ttc.base_addr +
                        TTC_CLK_CNTRL_OFFSET);

                psv = (ttccs->scale_clk_ctrl_reg_old &
                                TTC_CLK_CNTRL_PSV_MASK) >>
                                TTC_CLK_CNTRL_PSV_SHIFT;
                if (ndata->new_rate < ndata->old_rate)
                        psv -= factor;
                else
                        psv += factor;

                /* prescaler within legal range? */
                if (psv & ~(TTC_CLK_CNTRL_PSV_MASK >> TTC_CLK_CNTRL_PSV_SHIFT))
                        return NOTIFY_BAD;

                ttccs->scale_clk_ctrl_reg_new = ttccs->scale_clk_ctrl_reg_old &
                        ~TTC_CLK_CNTRL_PSV_MASK;
                ttccs->scale_clk_ctrl_reg_new |= psv << TTC_CLK_CNTRL_PSV_SHIFT;


                /* 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 */
                writel_relaxed(ttccs->scale_clk_ctrl_reg_new,
                               ttccs->ttc.base_addr + TTC_CLK_CNTRL_OFFSET);
                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 */
                writel_relaxed(ttccs->scale_clk_ctrl_reg_new,
                               ttccs->ttc.base_addr + TTC_CLK_CNTRL_OFFSET);
                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 */
                writel_relaxed(ttccs->scale_clk_ctrl_reg_old,
                               ttccs->ttc.base_addr + TTC_CLK_CNTRL_OFFSET);
                /* fall through */
        default:
                return NOTIFY_DONE;
        }

        return NOTIFY_DONE;
}

static int __init ttc_setup_clocksource(struct clk *clk, void __iomem *base,
                                         u32 timer_width)
{
        struct ttc_timer_clocksource *ttccs;
        int err;

        ttccs = kzalloc(sizeof(*ttccs), GFP_KERNEL);
        if (!ttccs)
                return -ENOMEM;

        ttccs->ttc.clk = clk;

        err = clk_prepare_enable(ttccs->ttc.clk);
        if (err) {
                kfree(ttccs);
                return err;
        }

        ttccs->ttc.freq = clk_get_rate(ttccs->ttc.clk);

        ttccs->ttc.clk_rate_change_nb.notifier_call =
                ttc_rate_change_clocksource_cb;
        ttccs->ttc.clk_rate_change_nb.next = NULL;

        err = clk_notifier_register(ttccs->ttc.clk,
                                    &ttccs->ttc.clk_rate_change_nb);
        if (err)
                pr_warn("Unable to register clock notifier.\n");

        ttccs->ttc.base_addr = base;
        ttccs->cs.name = "ttc_clocksource";
        ttccs->cs.rating = 200;
        ttccs->cs.read = __ttc_clocksource_read;
        ttccs->cs.mask = CLOCKSOURCE_MASK(timer_width);
        ttccs->cs.flags = CLOCK_SOURCE_IS_CONTINUOUS;

        /*
         * Setup the clock source counter to be an incrementing counter
         * with no interrupt and it rolls over at 0xFFFF. Pre-scale
         * it by 32 also. Let it start running now.
         */
        writel_relaxed(0x0,  ttccs->ttc.base_addr + TTC_IER_OFFSET);
        writel_relaxed(CLK_CNTRL_PRESCALE | CLK_CNTRL_PRESCALE_EN,
                     ttccs->ttc.base_addr + TTC_CLK_CNTRL_OFFSET);
        writel_relaxed(CNT_CNTRL_RESET,
                     ttccs->ttc.base_addr + TTC_CNT_CNTRL_OFFSET);

        err = clocksource_register_hz(&ttccs->cs, ttccs->ttc.freq / PRESCALE);
        if (err) {
                kfree(ttccs);
                return err;
        }

        ttc_sched_clock_val_reg = base + TTC_COUNT_VAL_OFFSET;
        sched_clock_register(ttc_sched_clock_read, timer_width,
                             ttccs->ttc.freq / PRESCALE);

        return 0;
}

static int ttc_rate_change_clockevent_cb(struct notifier_block *nb,
                unsigned long event, void *data)
{
        struct clk_notifier_data *ndata = data;
        struct ttc_timer *ttc = to_ttc_timer(nb);
        struct ttc_timer_clockevent *ttcce = container_of(ttc,
                        struct ttc_timer_clockevent, ttc);

        switch (event) {
        case POST_RATE_CHANGE:
                /* update cached frequency */
                ttc->freq = ndata->new_rate;

                clockevents_update_freq(&ttcce->ce, ndata->new_rate / PRESCALE);

                /* fall through */
        case PRE_RATE_CHANGE:
        case ABORT_RATE_CHANGE:
        default:
                return NOTIFY_DONE;
        }
}

static int __init ttc_setup_clockevent(struct clk *clk,
                                       void __iomem *base, u32 irq)
{
        struct ttc_timer_clockevent *ttcce;
        int err;

        ttcce = kzalloc(sizeof(*ttcce), GFP_KERNEL);
        if (!ttcce)
                return -ENOMEM;

        ttcce->ttc.clk = clk;

        err = clk_prepare_enable(ttcce->ttc.clk);
        if (err) {
                kfree(ttcce);
                return err;
        }

        ttcce->ttc.clk_rate_change_nb.notifier_call =
                ttc_rate_change_clockevent_cb;
        ttcce->ttc.clk_rate_change_nb.next = NULL;

        err = clk_notifier_register(ttcce->ttc.clk,
                                    &ttcce->ttc.clk_rate_change_nb);
        if (err) {
                pr_warn("Unable to register clock notifier.\n");
                return err;
        }

        ttcce->ttc.freq = clk_get_rate(ttcce->ttc.clk);

        ttcce->ttc.base_addr = base;
        ttcce->ce.name = "ttc_clockevent";
        ttcce->ce.features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT;
        ttcce->ce.set_next_event = ttc_set_next_event;
        ttcce->ce.set_state_shutdown = ttc_shutdown;
        ttcce->ce.set_state_periodic = ttc_set_periodic;
        ttcce->ce.set_state_oneshot = ttc_shutdown;
        ttcce->ce.tick_resume = ttc_resume;
        ttcce->ce.rating = 200;
        ttcce->ce.irq = irq;
        ttcce->ce.cpumask = cpu_possible_mask;

        /*
         * Setup the clock event timer to be an interval timer which
         * is prescaled by 32 using the interval interrupt. Leave it
         * disabled for now.
         */
        writel_relaxed(0x23, ttcce->ttc.base_addr + TTC_CNT_CNTRL_OFFSET);
        writel_relaxed(CLK_CNTRL_PRESCALE | CLK_CNTRL_PRESCALE_EN,
                     ttcce->ttc.base_addr + TTC_CLK_CNTRL_OFFSET);
        writel_relaxed(0x1,  ttcce->ttc.base_addr + TTC_IER_OFFSET);

        err = request_irq(irq, ttc_clock_event_interrupt,
                          IRQF_TIMER, ttcce->ce.name, ttcce);
        if (err) {
                kfree(ttcce);
                return err;
        }

        clockevents_config_and_register(&ttcce->ce,
                        ttcce->ttc.freq / PRESCALE, 1, 0xfffe);

        return 0;
}

/**
 * ttc_timer_init - Initialize the timer
 *
 * Initializes the timer hardware and register the clock source and clock event
 * timers with Linux kernal timer framework
 */
static int __init ttc_timer_init(struct device_node *timer)
{
        unsigned int irq;
        void __iomem *timer_baseaddr;
        struct clk *clk_cs, *clk_ce;
        static int initialized;
        int clksel, ret;
        u32 timer_width = 16;

        if (initialized)
                return 0;

        initialized = 1;

        /*
         * Get the 1st Triple Timer Counter (TTC) block from the device tree
         * and use it. Note that the event timer uses the interrupt and it's the
         * 2nd TTC hence the irq_of_parse_and_map(,1)
         */
        timer_baseaddr = of_iomap(timer, 0);
        if (!timer_baseaddr) {
                pr_err("ERROR: invalid timer base address\n");
                return -ENXIO;
        }

        irq = irq_of_parse_and_map(timer, 1);
        if (irq <= 0) {
                pr_err("ERROR: invalid interrupt number\n");
                return -EINVAL;
        }

        of_property_read_u32(timer, "timer-width", &timer_width);

        clksel = readl_relaxed(timer_baseaddr + TTC_CLK_CNTRL_OFFSET);
        clksel = !!(clksel & TTC_CLK_CNTRL_CSRC_MASK);
        clk_cs = of_clk_get(timer, clksel);
        if (IS_ERR(clk_cs)) {
                pr_err("ERROR: timer input clock not found\n");
                return PTR_ERR(clk_cs);
        }

        clksel = readl_relaxed(timer_baseaddr + 4 + TTC_CLK_CNTRL_OFFSET);
        clksel = !!(clksel & TTC_CLK_CNTRL_CSRC_MASK);
        clk_ce = of_clk_get(timer, clksel);
        if (IS_ERR(clk_ce)) {
                pr_err("ERROR: timer input clock not found\n");
                return PTR_ERR(clk_ce);
        }

        ret = ttc_setup_clocksource(clk_cs, timer_baseaddr, timer_width);
        if (ret)
                return ret;

        ret = ttc_setup_clockevent(clk_ce, timer_baseaddr + 4, irq);
        if (ret)
                return ret;

        pr_info("%s #0 at %p, irq=%d\n", timer->name, timer_baseaddr, irq);

        return 0;
}

CLOCKSOURCE_OF_DECLARE(ttc, "cdns,ttc", ttc_timer_init);