/*
 * at91sam926x_time.c - Periodic Interval Timer (PIT) for at91sam926x
 *
 * Copyright (C) 2005-2006 M. Amine SAYA, ATMEL Rousset, France
 * Revision      2005 M. Nicolas Diremdjian, ATMEL Rousset, France
 * Converted to ClockSource/ClockEvents by David Brownell.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#define pr_fmt(fmt)     "AT91: PIT: " fmt

#include <linux/clk.h>
#include <linux/clockchips.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/kernel.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_irq.h>
#include <linux/slab.h>

#define AT91_PIT_MR             0x00                    /* Mode Register */
#define AT91_PIT_PITIEN                 BIT(25)                 /* Timer Interrupt Enable */
#define AT91_PIT_PITEN                  BIT(24)                 /* Timer Enabled */
#define AT91_PIT_PIV                    GENMASK(19, 0)          /* Periodic Interval Value */

#define AT91_PIT_SR             0x04                    /* Status Register */
#define AT91_PIT_PITS                   BIT(0)                  /* Timer Status */

#define AT91_PIT_PIVR           0x08                    /* Periodic Interval Value Register */
#define AT91_PIT_PIIR           0x0c                    /* Periodic Interval Image Register */
#define AT91_PIT_PICNT                  GENMASK(31, 20)         /* Interval Counter */
#define AT91_PIT_CPIV                   GENMASK(19, 0)          /* Inverval Value */

#define PIT_CPIV(x)     ((x) & AT91_PIT_CPIV)
#define PIT_PICNT(x)    (((x) & AT91_PIT_PICNT) >> 20)

struct pit_data {
        struct clock_event_device       clkevt;
        struct clocksource              clksrc;

        void __iomem    *base;
        u32             cycle;
        u32             cnt;
        unsigned int    irq;
        struct clk      *mck;
};

static inline struct pit_data *clksrc_to_pit_data(struct clocksource *clksrc)
{
        return container_of(clksrc, struct pit_data, clksrc);
}

static inline struct pit_data *clkevt_to_pit_data(struct clock_event_device *clkevt)
{
        return container_of(clkevt, struct pit_data, clkevt);
}

static inline unsigned int pit_read(void __iomem *base, unsigned int reg_offset)
{
        return readl_relaxed(base + reg_offset);
}

static inline void pit_write(void __iomem *base, unsigned int reg_offset, unsigned long value)
{
        writel_relaxed(value, base + reg_offset);
}

/*
 * Clocksource:  just a monotonic counter of MCK/16 cycles.
 * We don't care whether or not PIT irqs are enabled.
 */
static cycle_t read_pit_clk(struct clocksource *cs)
{
        struct pit_data *data = clksrc_to_pit_data(cs);
        unsigned long flags;
        u32 elapsed;
        u32 t;

        raw_local_irq_save(flags);
        elapsed = data->cnt;
        t = pit_read(data->base, AT91_PIT_PIIR);
        raw_local_irq_restore(flags);

        elapsed += PIT_PICNT(t) * data->cycle;
        elapsed += PIT_CPIV(t);
        return elapsed;
}

static int pit_clkevt_shutdown(struct clock_event_device *dev)
{
        struct pit_data *data = clkevt_to_pit_data(dev);

        /* disable irq, leaving the clocksource active */
        pit_write(data->base, AT91_PIT_MR, (data->cycle - 1) | AT91_PIT_PITEN);
        return 0;
}

/*
 * Clockevent device:  interrupts every 1/HZ (== pit_cycles * MCK/16)
 */
static int pit_clkevt_set_periodic(struct clock_event_device *dev)
{
        struct pit_data *data = clkevt_to_pit_data(dev);

        /* update clocksource counter */
        data->cnt += data->cycle * PIT_PICNT(pit_read(data->base, AT91_PIT_PIVR));
        pit_write(data->base, AT91_PIT_MR,
                  (data->cycle - 1) | AT91_PIT_PITEN | AT91_PIT_PITIEN);
        return 0;
}

static void at91sam926x_pit_suspend(struct clock_event_device *cedev)
{
        struct pit_data *data = clkevt_to_pit_data(cedev);

        /* Disable timer */
        pit_write(data->base, AT91_PIT_MR, 0);
}

static void at91sam926x_pit_reset(struct pit_data *data)
{
        /* Disable timer and irqs */
        pit_write(data->base, AT91_PIT_MR, 0);

        /* Clear any pending interrupts, wait for PIT to stop counting */
        while (PIT_CPIV(pit_read(data->base, AT91_PIT_PIVR)) != 0)
                cpu_relax();

        /* Start PIT but don't enable IRQ */
        pit_write(data->base, AT91_PIT_MR,
                  (data->cycle - 1) | AT91_PIT_PITEN);
}

static void at91sam926x_pit_resume(struct clock_event_device *cedev)
{
        struct pit_data *data = clkevt_to_pit_data(cedev);

        at91sam926x_pit_reset(data);
}

/*
 * IRQ handler for the timer.
 */
static irqreturn_t at91sam926x_pit_interrupt(int irq, void *dev_id)
{
        struct pit_data *data = dev_id;

        /* The PIT interrupt may be disabled, and is shared */
        if (clockevent_state_periodic(&data->clkevt) &&
            (pit_read(data->base, AT91_PIT_SR) & AT91_PIT_PITS)) {
                /* Get number of ticks performed before irq, and ack it */
                data->cnt += data->cycle * PIT_PICNT(pit_read(data->base,
                                                              AT91_PIT_PIVR));
                data->clkevt.event_handler(&data->clkevt);

                return IRQ_HANDLED;
        }

        return IRQ_NONE;
}

/*
 * Set up both clocksource and clockevent support.
 */
static int __init at91sam926x_pit_dt_init(struct device_node *node)
{
        unsigned long   pit_rate;
        unsigned        bits;
        int             ret;
        struct pit_data *data;

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

        data->base = of_iomap(node, 0);
        if (!data->base) {
                pr_err("Could not map PIT address\n");
                return -ENXIO;
        }

        data->mck = of_clk_get(node, 0);
        if (IS_ERR(data->mck)) {
                pr_err("Unable to get mck clk\n");
                return PTR_ERR(data->mck);
        }

        ret = clk_prepare_enable(data->mck);
        if (ret) {
                pr_err("Unable to enable mck\n");
                return ret;
        }

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

        /*
         * Use our actual MCK to figure out how many MCK/16 ticks per
         * 1/HZ period (instead of a compile-time constant LATCH).
         */
        pit_rate = clk_get_rate(data->mck) / 16;
        data->cycle = DIV_ROUND_CLOSEST(pit_rate, HZ);
        WARN_ON(((data->cycle - 1) & ~AT91_PIT_PIV) != 0);

        /* Initialize and enable the timer */
        at91sam926x_pit_reset(data);

        /*
         * Register clocksource.  The high order bits of PIV are unused,
         * so this isn't a 32-bit counter unless we get clockevent irqs.
         */
        bits = 12 /* PICNT */ + ilog2(data->cycle) /* PIV */;
        data->clksrc.mask = CLOCKSOURCE_MASK(bits);
        data->clksrc.name = "pit";
        data->clksrc.rating = 175;
        data->clksrc.read = read_pit_clk;
        data->clksrc.flags = CLOCK_SOURCE_IS_CONTINUOUS;
        
        ret = clocksource_register_hz(&data->clksrc, pit_rate);
        if (ret) {
                pr_err("Failed to register clocksource");
                return ret;
        }

        /* Set up irq handler */
        ret = request_irq(data->irq, at91sam926x_pit_interrupt,
                          IRQF_SHARED | IRQF_TIMER | IRQF_IRQPOLL,
                          "at91_tick", data);
        if (ret) {
                pr_err("Unable to setup IRQ\n");
                return ret;
        }

        /* Set up and register clockevents */
        data->clkevt.name = "pit";
        data->clkevt.features = CLOCK_EVT_FEAT_PERIODIC;
        data->clkevt.shift = 32;
        data->clkevt.mult = div_sc(pit_rate, NSEC_PER_SEC, data->clkevt.shift);
        data->clkevt.rating = 100;
        data->clkevt.cpumask = cpumask_of(0);

        data->clkevt.set_state_shutdown = pit_clkevt_shutdown;
        data->clkevt.set_state_periodic = pit_clkevt_set_periodic;
        data->clkevt.resume = at91sam926x_pit_resume;
        data->clkevt.suspend = at91sam926x_pit_suspend;
        clockevents_register_device(&data->clkevt);

        return 0;
}
CLOCKSOURCE_OF_DECLARE(at91sam926x_pit, "atmel,at91sam9260-pit",
                       at91sam926x_pit_dt_init);