/*
 * linux/arch/arm/mach-at91/at91rm9200_time.c
 *
 *  Copyright (C) 2003 SAN People
 *  Copyright (C) 2003 ATMEL
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/kernel.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/clk.h>
#include <linux/clockchips.h>
#include <linux/export.h>
#include <linux/mfd/syscon.h>
#include <linux/mfd/syscon/atmel-st.h>
#include <linux/of_irq.h>
#include <linux/regmap.h>

static unsigned long last_crtr;
static u32 irqmask;
static struct clock_event_device clkevt;
static struct regmap *regmap_st;
static int timer_latch;

/*
 * The ST_CRTR is updated asynchronously to the master clock ... but
 * the updates as seen by the CPU don't seem to be strictly monotonic.
 * Waiting until we read the same value twice avoids glitching.
 */
static inline unsigned long read_CRTR(void)
{
        unsigned int x1, x2;

        regmap_read(regmap_st, AT91_ST_CRTR, &x1);
        do {
                regmap_read(regmap_st, AT91_ST_CRTR, &x2);
                if (x1 == x2)
                        break;
                x1 = x2;
        } while (1);
        return x1;
}

/*
 * IRQ handler for the timer.
 */
static irqreturn_t at91rm9200_timer_interrupt(int irq, void *dev_id)
{
        u32 sr;

        regmap_read(regmap_st, AT91_ST_SR, &sr);
        sr &= irqmask;

        /*
         * irqs should be disabled here, but as the irq is shared they are only
         * guaranteed to be off if the timer irq is registered first.
         */
        WARN_ON_ONCE(!irqs_disabled());

        /* simulate "oneshot" timer with alarm */
        if (sr & AT91_ST_ALMS) {
                clkevt.event_handler(&clkevt);
                return IRQ_HANDLED;
        }

        /* periodic mode should handle delayed ticks */
        if (sr & AT91_ST_PITS) {
                u32     crtr = read_CRTR();

                while (((crtr - last_crtr) & AT91_ST_CRTV) >= timer_latch) {
                        last_crtr += timer_latch;
                        clkevt.event_handler(&clkevt);
                }
                return IRQ_HANDLED;
        }

        /* this irq is shared ... */
        return IRQ_NONE;
}

static u64 read_clk32k(struct clocksource *cs)
{
        return read_CRTR();
}

static struct clocksource clk32k = {
        .name           = "32k_counter",
        .rating         = 150,
        .read           = read_clk32k,
        .mask           = CLOCKSOURCE_MASK(20),
        .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
};

static void clkdev32k_disable_and_flush_irq(void)
{
        unsigned int val;

        /* Disable and flush pending timer interrupts */
        regmap_write(regmap_st, AT91_ST_IDR, AT91_ST_PITS | AT91_ST_ALMS);
        regmap_read(regmap_st, AT91_ST_SR, &val);
        last_crtr = read_CRTR();
}

static int clkevt32k_shutdown(struct clock_event_device *evt)
{
        clkdev32k_disable_and_flush_irq();
        irqmask = 0;
        regmap_write(regmap_st, AT91_ST_IER, irqmask);
        return 0;
}

static int clkevt32k_set_oneshot(struct clock_event_device *dev)
{
        clkdev32k_disable_and_flush_irq();

        /*
         * ALM for oneshot irqs, set by next_event()
         * before 32 seconds have passed.
         */
        irqmask = AT91_ST_ALMS;
        regmap_write(regmap_st, AT91_ST_RTAR, last_crtr);
        regmap_write(regmap_st, AT91_ST_IER, irqmask);
        return 0;
}

static int clkevt32k_set_periodic(struct clock_event_device *dev)
{
        clkdev32k_disable_and_flush_irq();

        /* PIT for periodic irqs; fixed rate of 1/HZ */
        irqmask = AT91_ST_PITS;
        regmap_write(regmap_st, AT91_ST_PIMR, timer_latch);
        regmap_write(regmap_st, AT91_ST_IER, irqmask);
        return 0;
}

static int
clkevt32k_next_event(unsigned long delta, struct clock_event_device *dev)
{
        u32             alm;
        int             status = 0;
        unsigned int    val;

        BUG_ON(delta < 2);

        /* The alarm IRQ uses absolute time (now+delta), not the relative
         * time (delta) in our calling convention.  Like all clockevents
         * using such "match" hardware, we have a race to defend against.
         *
         * Our defense here is to have set up the clockevent device so the
         * delta is at least two.  That way we never end up writing RTAR
         * with the value then held in CRTR ... which would mean the match
         * wouldn't trigger until 32 seconds later, after CRTR wraps.
         */
        alm = read_CRTR();

        /* Cancel any pending alarm; flush any pending IRQ */
        regmap_write(regmap_st, AT91_ST_RTAR, alm);
        regmap_read(regmap_st, AT91_ST_SR, &val);

        /* Schedule alarm by writing RTAR. */
        alm += delta;
        regmap_write(regmap_st, AT91_ST_RTAR, alm);

        return status;
}

static struct clock_event_device clkevt = {
        .name                   = "at91_tick",
        .features               = CLOCK_EVT_FEAT_PERIODIC |
                                  CLOCK_EVT_FEAT_ONESHOT,
        .rating                 = 150,
        .set_next_event         = clkevt32k_next_event,
        .set_state_shutdown     = clkevt32k_shutdown,
        .set_state_periodic     = clkevt32k_set_periodic,
        .set_state_oneshot      = clkevt32k_set_oneshot,
        .tick_resume            = clkevt32k_shutdown,
};

/*
 * ST (system timer) module supports both clockevents and clocksource.
 */
static int __init atmel_st_timer_init(struct device_node *node)
{
        struct clk *sclk;
        unsigned int sclk_rate, val;
        int irq, ret;

        regmap_st = syscon_node_to_regmap(node);
        if (IS_ERR(regmap_st)) {
                pr_err("Unable to get regmap\n");
                return PTR_ERR(regmap_st);
        }

        /* Disable all timer interrupts, and clear any pending ones */
        regmap_write(regmap_st, AT91_ST_IDR,
                AT91_ST_PITS | AT91_ST_WDOVF | AT91_ST_RTTINC | AT91_ST_ALMS);
        regmap_read(regmap_st, AT91_ST_SR, &val);

        /* Get the interrupts property */
        irq  = irq_of_parse_and_map(node, 0);
        if (!irq) {
                pr_err("Unable to get IRQ from DT\n");
                return -EINVAL;
        }

        /* Make IRQs happen for the system timer */
        ret = request_irq(irq, at91rm9200_timer_interrupt,
                          IRQF_SHARED | IRQF_TIMER | IRQF_IRQPOLL,
                          "at91_tick", regmap_st);
        if (ret) {
                pr_err("Unable to setup IRQ\n");
                return ret;
        }

        sclk = of_clk_get(node, 0);
        if (IS_ERR(sclk)) {
                pr_err("Unable to get slow clock\n");
                return PTR_ERR(sclk);
        }

        ret = clk_prepare_enable(sclk);
        if (ret) {
                pr_err("Could not enable slow clock\n");
                return ret;
        }

        sclk_rate = clk_get_rate(sclk);
        if (!sclk_rate) {
                pr_err("Invalid slow clock rate\n");
                return -EINVAL;
        }
        timer_latch = (sclk_rate + HZ / 2) / HZ;

        /* The 32KiHz "Slow Clock" (tick every 30517.58 nanoseconds) is used
         * directly for the clocksource and all clockevents, after adjusting
         * its prescaler from the 1 Hz default.
         */
        regmap_write(regmap_st, AT91_ST_RTMR, 1);

        /* Setup timer clockevent, with minimum of two ticks (important!!) */
        clkevt.cpumask = cpumask_of(0);
        clockevents_config_and_register(&clkevt, sclk_rate,
                                        2, AT91_ST_ALMV);

        /* register clocksource */
        return clocksource_register_hz(&clk32k, sclk_rate);
}
TIMER_OF_DECLARE(atmel_st_timer, "atmel,at91rm9200-st",
                       atmel_st_timer_init);