/* linux/arch/arm/plat-s3c24xx/time.c
 *
 * Copyright (C) 2003-2005 Simtec Electronics
 *      Ben Dooks, <ben@simtec.co.uk>
 *
 * 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/sched.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/err.h>
#include <linux/clk.h>
#include <linux/io.h>
#include <linux/platform_device.h>

#include <asm/system.h>
#include <asm/leds.h>
#include <asm/mach-types.h>

#include <asm/irq.h>
#include <mach/map.h>
#include <plat/regs-timer.h>
#include <mach/regs-irq.h>
#include <asm/mach/time.h>
#include <mach/tick.h>

#include <plat/clock.h>
#include <plat/cpu.h>

static unsigned long timer_startval;
static unsigned long timer_usec_ticks;

#ifndef TICK_MAX
#define TICK_MAX (0xffff)
#endif

#define TIMER_USEC_SHIFT 16

/* we use the shifted arithmetic to work out the ratio of timer ticks
 * to usecs, as often the peripheral clock is not a nice even multiple
 * of 1MHz.
 *
 * shift of 14 and 15 are too low for the 12MHz, 16 seems to be ok
 * for the current HZ value of 200 without producing overflows.
 *
 * Original patch by Dimitry Andric, updated by Ben Dooks
*/


/* timer_mask_usec_ticks
 *
 * given a clock and divisor, make the value to pass into timer_ticks_to_usec
 * to scale the ticks into usecs
*/

static inline unsigned long
timer_mask_usec_ticks(unsigned long scaler, unsigned long pclk)
{
        unsigned long den = pclk / 1000;

        return ((1000 << TIMER_USEC_SHIFT) * scaler + (den >> 1)) / den;
}

/* timer_ticks_to_usec
 *
 * convert timer ticks to usec.
*/

static inline unsigned long timer_ticks_to_usec(unsigned long ticks)
{
        unsigned long res;

        res = ticks * timer_usec_ticks;
        res += 1 << (TIMER_USEC_SHIFT - 4);     /* round up slightly */

        return res >> TIMER_USEC_SHIFT;
}

/***
 * Returns microsecond  since last clock interrupt.  Note that interrupts
 * will have been disabled by do_gettimeoffset()
 * IRQs are disabled before entering here from do_gettimeofday()
 */

static unsigned long s3c2410_gettimeoffset (void)
{
        unsigned long tdone;
        unsigned long tval;

        /* work out how many ticks have gone since last timer interrupt */

        tval =  __raw_readl(S3C2410_TCNTO(4));
        tdone = timer_startval - tval;

        /* check to see if there is an interrupt pending */

        if (s3c24xx_ostimer_pending()) {
                /* re-read the timer, and try and fix up for the missed
                 * interrupt. Note, the interrupt may go off before the
                 * timer has re-loaded from wrapping.
                 */

                tval =  __raw_readl(S3C2410_TCNTO(4));
                tdone = timer_startval - tval;

                if (tval != 0)
                        tdone += timer_startval;
        }

        return timer_ticks_to_usec(tdone);
}


/*
 * IRQ handler for the timer
 */
static irqreturn_t
s3c2410_timer_interrupt(int irq, void *dev_id)
{
        timer_tick();
        return IRQ_HANDLED;
}

static struct irqaction s3c2410_timer_irq = {
        .name           = "S3C2410 Timer Tick",
        .flags          = IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
        .handler        = s3c2410_timer_interrupt,
};

#define use_tclk1_12() ( \
        machine_is_bast()       || \
        machine_is_vr1000()     || \
        machine_is_anubis()     || \
        machine_is_osiris())

static struct clk *tin;
static struct clk *tdiv;
static struct clk *timerclk;

/*
 * Set up timer interrupt, and return the current time in seconds.
 *
 * Currently we only use timer4, as it is the only timer which has no
 * other function that can be exploited externally
 */
static void s3c2410_timer_setup (void)
{
        unsigned long tcon;
        unsigned long tcnt;
        unsigned long tcfg1;
        unsigned long tcfg0;

        tcnt = TICK_MAX;  /* default value for tcnt */

        /* configure the system for whichever machine is in use */

        if (use_tclk1_12()) {
                /* timer is at 12MHz, scaler is 1 */
                timer_usec_ticks = timer_mask_usec_ticks(1, 12000000);
                tcnt = 12000000 / HZ;

                tcfg1 = __raw_readl(S3C2410_TCFG1);
                tcfg1 &= ~S3C2410_TCFG1_MUX4_MASK;
                tcfg1 |= S3C2410_TCFG1_MUX4_TCLK1;
                __raw_writel(tcfg1, S3C2410_TCFG1);
        } else {
                unsigned long pclk;
                struct clk *tscaler;

                /* for the h1940 (and others), we use the pclk from the core
                 * to generate the timer values. since values around 50 to
                 * 70MHz are not values we can directly generate the timer
                 * value from, we need to pre-scale and divide before using it.
                 *
                 * for instance, using 50.7MHz and dividing by 6 gives 8.45MHz
                 * (8.45 ticks per usec)
                 */

                pclk = clk_get_rate(timerclk);

                /* configure clock tick */

                timer_usec_ticks = timer_mask_usec_ticks(6, pclk);

                tscaler = clk_get_parent(tdiv);

                clk_set_rate(tscaler, pclk / 3);
                clk_set_rate(tdiv, pclk / 6);
                clk_set_parent(tin, tdiv);

                tcnt = clk_get_rate(tin) / HZ;
        }

        tcon = __raw_readl(S3C2410_TCON);
        tcfg0 = __raw_readl(S3C2410_TCFG0);
        tcfg1 = __raw_readl(S3C2410_TCFG1);

        /* timers reload after counting zero, so reduce the count by 1 */

        tcnt--;

        printk(KERN_DEBUG "timer tcon=%08lx, tcnt %04lx, tcfg %08lx,%08lx, usec %08lx\n",
               tcon, tcnt, tcfg0, tcfg1, timer_usec_ticks);

        /* check to see if timer is within 16bit range... */
        if (tcnt > TICK_MAX) {
                panic("setup_timer: HZ is too small, cannot configure timer!");
                return;
        }

        __raw_writel(tcfg1, S3C2410_TCFG1);
        __raw_writel(tcfg0, S3C2410_TCFG0);

        timer_startval = tcnt;
        __raw_writel(tcnt, S3C2410_TCNTB(4));

        /* ensure timer is stopped... */

        tcon &= ~(7<<20);
        tcon |= S3C2410_TCON_T4RELOAD;
        tcon |= S3C2410_TCON_T4MANUALUPD;

        __raw_writel(tcon, S3C2410_TCON);
        __raw_writel(tcnt, S3C2410_TCNTB(4));
        __raw_writel(tcnt, S3C2410_TCMPB(4));

        /* start the timer running */
        tcon |= S3C2410_TCON_T4START;
        tcon &= ~S3C2410_TCON_T4MANUALUPD;
        __raw_writel(tcon, S3C2410_TCON);
}

static void __init s3c2410_timer_resources(void)
{
        struct platform_device tmpdev;

        tmpdev.dev.bus = &platform_bus_type;
        tmpdev.id = 4;

        timerclk = clk_get(NULL, "timers");
        if (IS_ERR(timerclk))
                panic("failed to get clock for system timer");

        clk_enable(timerclk);

        if (!use_tclk1_12()) {
                tin = clk_get(&tmpdev.dev, "pwm-tin");
                if (IS_ERR(tin))
                        panic("failed to get pwm-tin clock for system timer");

                tdiv = clk_get(&tmpdev.dev, "pwm-tdiv");
                if (IS_ERR(tdiv))
                        panic("failed to get pwm-tdiv clock for system timer");
        }

        clk_enable(tin);
}

static void __init s3c2410_timer_init(void)
{
        s3c2410_timer_resources();
        s3c2410_timer_setup();
        setup_irq(IRQ_TIMER4, &s3c2410_timer_irq);
}

struct sys_timer s3c24xx_timer = {
        .init           = s3c2410_timer_init,
        .offset         = s3c2410_gettimeoffset,
        .resume         = s3c2410_timer_setup
};