/*
 * 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/clk-provider.h>

/*
 * This driver configures the 2 16-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

/*
 * 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)

/**
 * struct ttc_timer - This definition defines local timer structure
 *
 * @base_addr:  Base address of timer
 * @clk:        Associated clock source
 * @clk_rate_change_nb  Notifier block for clock rate changes
 */
struct ttc_timer {
        void __iomem *base_addr;
        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 {
        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)

/**
 * 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 = __raw_readl(timer->base_addr + TTC_CNT_CNTRL_OFFSET);
        ctrl_reg |= TTC_CNT_CNTRL_DISABLE_MASK;
        __raw_writel(ctrl_reg, timer->base_addr + TTC_CNT_CNTRL_OFFSET);

        __raw_writel(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;
        __raw_writel(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 */
        __raw_readl(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)__raw_readl(timer->base_addr +
                                TTC_COUNT_VAL_OFFSET);
}

/**
 * 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_mode - Sets the mode of timer
 *
 * @mode:       Mode to be set
 * @evt:        Address of clock event instance
 **/
static void ttc_set_mode(enum clock_event_mode mode,
                                        struct clock_event_device *evt)
{
        struct ttc_timer_clockevent *ttce = to_ttc_timer_clkevent(evt);
        struct ttc_timer *timer = &ttce->ttc;
        u32 ctrl_reg;

        switch (mode) {
        case CLOCK_EVT_MODE_PERIODIC:
                ttc_set_interval(timer,
                                DIV_ROUND_CLOSEST(clk_get_rate(ttce->ttc.clk),
                                        PRESCALE * HZ));
                break;
        case CLOCK_EVT_MODE_ONESHOT:
        case CLOCK_EVT_MODE_UNUSED:
        case CLOCK_EVT_MODE_SHUTDOWN:
                ctrl_reg = __raw_readl(timer->base_addr +
                                        TTC_CNT_CNTRL_OFFSET);
                ctrl_reg |= TTC_CNT_CNTRL_DISABLE_MASK;
                __raw_writel(ctrl_reg,
                                timer->base_addr + TTC_CNT_CNTRL_OFFSET);
                break;
        case CLOCK_EVT_MODE_RESUME:
                ctrl_reg = __raw_readl(timer->base_addr +
                                        TTC_CNT_CNTRL_OFFSET);
                ctrl_reg &= ~TTC_CNT_CNTRL_DISABLE_MASK;
                __raw_writel(ctrl_reg,
                                timer->base_addr + TTC_CNT_CNTRL_OFFSET);
                break;
        }
}

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 POST_RATE_CHANGE:
                /*
                 * Do whatever is necessary to maintain a proper time base
                 *
                 * I cannot find a way to adjust the currently used clocksource
                 * to the new frequency. __clocksource_updatefreq_hz() sounds
                 * good, but does not work. Not sure what's that missing.
                 *
                 * This approach works, but triggers two clocksource switches.
                 * The first after unregister to clocksource jiffies. And
                 * another one after the register to the newly registered timer.
                 *
                 * Alternatively we could 'waste' another HW timer to ping pong
                 * between clock sources. That would also use one register and
                 * one unregister call, but only trigger one clocksource switch
                 * for the cost of another HW timer used by the OS.
                 */
                clocksource_unregister(&ttccs->cs);
                clocksource_register_hz(&ttccs->cs,
                                ndata->new_rate / PRESCALE);
                /* fall through */
        case PRE_RATE_CHANGE:
        case ABORT_RATE_CHANGE:
        default:
                return NOTIFY_DONE;
        }
}

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

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

        ttccs->ttc.clk = clk;

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

        ttccs->ttc.clk_rate_change_nb.notifier_call =
                ttc_rate_change_clocksource_cb;
        ttccs->ttc.clk_rate_change_nb.next = NULL;
        if (clk_notifier_register(ttccs->ttc.clk,
                                &ttccs->ttc.clk_rate_change_nb))
                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(16);
        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.
         */
        __raw_writel(0x0,  ttccs->ttc.base_addr + TTC_IER_OFFSET);
        __raw_writel(CLK_CNTRL_PRESCALE | CLK_CNTRL_PRESCALE_EN,
                     ttccs->ttc.base_addr + TTC_CLK_CNTRL_OFFSET);
        __raw_writel(CNT_CNTRL_RESET,
                     ttccs->ttc.base_addr + TTC_CNT_CNTRL_OFFSET);

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

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:
        {
                unsigned long flags;

                /*
                 * clockevents_update_freq should be called with IRQ disabled on
                 * the CPU the timer provides events for. The timer we use is
                 * common to both CPUs, not sure if we need to run on both
                 * cores.
                 */
                local_irq_save(flags);
                clockevents_update_freq(&ttcce->ce,
                                ndata->new_rate / PRESCALE);
                local_irq_restore(flags);

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

static void __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 (WARN_ON(!ttcce))
                return;

        ttcce->ttc.clk = clk;

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

        ttcce->ttc.clk_rate_change_nb.notifier_call =
                ttc_rate_change_clockevent_cb;
        ttcce->ttc.clk_rate_change_nb.next = NULL;
        if (clk_notifier_register(ttcce->ttc.clk,
                                &ttcce->ttc.clk_rate_change_nb))
                pr_warn("Unable to register clock notifier.\n");

        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_mode = ttc_set_mode;
        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.
         */
        __raw_writel(0x23, ttcce->ttc.base_addr + TTC_CNT_CNTRL_OFFSET);
        __raw_writel(CLK_CNTRL_PRESCALE | CLK_CNTRL_PRESCALE_EN,
                     ttcce->ttc.base_addr + TTC_CLK_CNTRL_OFFSET);
        __raw_writel(0x1,  ttcce->ttc.base_addr + TTC_IER_OFFSET);

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

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

/**
 * 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 void __init ttc_timer_init(struct device_node *timer)
{
        unsigned int irq;
        void __iomem *timer_baseaddr;
        struct clk *clk;
        static int initialized;

        if (initialized)
                return;

        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");
                BUG();
        }

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

        clk = of_clk_get_by_name(timer, "cpu_1x");
        if (IS_ERR(clk)) {
                pr_err("ERROR: timer input clock not found\n");
                BUG();
        }

        ttc_setup_clocksource(clk, timer_baseaddr);
        ttc_setup_clockevent(clk, timer_baseaddr + 4, irq);

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

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