time.c

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/*
 * arch/arm/plat-spear/time.c
 *
 * Copyright (C) 2010 ST Microelectronics
 * Shiraz Hashim<[email protected]>
 *
 * This file is licensed under the terms of the GNU General Public
 * License version 2. This program is licensed "as is" without any
 * warranty of any kind, whether express or implied.
 */

#include <linux/clk.h>
#include <linux/clockchips.h>
#include <linux/clocksource.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/ioport.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/of_irq.h>
#include <linux/of_address.h>
#include <linux/time.h>
#include <linux/irq.h>
#include <asm/mach/time.h>
#include <mach/generic.h>

/*
 * We would use TIMER0 and TIMER1 as clockevent and clocksource.
 * Timer0 and Timer1 both belong to same gpt block in cpu subbsystem. Further
 * they share same functional clock. Any change in one's functional clock will
 * also affect other timer.
 */

#define CLKEVT  0   /* gpt0, channel0 as clockevent */
#define CLKSRC  1   /* gpt0, channel1 as clocksource */

/* Register offsets, x is channel number */
#define CR(x)       ((x) * 0x80 + 0x80)
#define IR(x)       ((x) * 0x80 + 0x84)
#define LOAD(x)     ((x) * 0x80 + 0x88)
#define COUNT(x)    ((x) * 0x80 + 0x8C)

/* Reg bit definitions */
#define CTRL_INT_ENABLE     0x0100
#define CTRL_ENABLE     0x0020
#define CTRL_ONE_SHOT       0x0010

#define CTRL_PRESCALER1     0x0
#define CTRL_PRESCALER2     0x1
#define CTRL_PRESCALER4     0x2
#define CTRL_PRESCALER8     0x3
#define CTRL_PRESCALER16    0x4
#define CTRL_PRESCALER32    0x5
#define CTRL_PRESCALER64    0x6
#define CTRL_PRESCALER128   0x7
#define CTRL_PRESCALER256   0x8

#define INT_STATUS      0x1

/*
 * Minimum clocksource/clockevent timer range in seconds
 */
#define SPEAR_MIN_RANGE 4

static __iomem void *gpt_base;
static struct clk *gpt_clk;

static void clockevent_set_mode(enum clock_event_mode mode,
                struct clock_event_device *clk_event_dev);
static int clockevent_next_event(unsigned long evt,
                 struct clock_event_device *clk_event_dev);

static void spear_clocksource_init(void)
{
    u32 tick_rate;
    u16 val;

    /* program the prescaler (/256)*/
    writew(CTRL_PRESCALER256, gpt_base + CR(CLKSRC));

    /* find out actual clock driving Timer */
    tick_rate = clk_get_rate(gpt_clk);
    tick_rate >>= CTRL_PRESCALER256;

    writew(0xFFFF, gpt_base + LOAD(CLKSRC));

    val = readw(gpt_base + CR(CLKSRC));
    val &= ~CTRL_ONE_SHOT;  /* autoreload mode */
    val |= CTRL_ENABLE ;
    writew(val, gpt_base + CR(CLKSRC));

    /* register the clocksource */
    clocksource_mmio_init(gpt_base + COUNT(CLKSRC), "tmr1", tick_rate,
        200, 16, clocksource_mmio_readw_up);
}

static struct clock_event_device clkevt = {
    .name = "tmr0",
    .features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
    .set_mode = clockevent_set_mode,
    .set_next_event = clockevent_next_event,
    .shift = 0, /* to be computed */
};

static void clockevent_set_mode(enum clock_event_mode mode,
                struct clock_event_device *clk_event_dev)
{
    u32 period;
    u16 val;

    /* stop the timer */
    val = readw(gpt_base + CR(CLKEVT));
    val &= ~CTRL_ENABLE;
    writew(val, gpt_base + CR(CLKEVT));

    switch (mode) {
    case CLOCK_EVT_MODE_PERIODIC:
        period = clk_get_rate(gpt_clk) / HZ;
        period >>= CTRL_PRESCALER16;
        writew(period, gpt_base + LOAD(CLKEVT));

        val = readw(gpt_base + CR(CLKEVT));
        val &= ~CTRL_ONE_SHOT;
        val |= CTRL_ENABLE | CTRL_INT_ENABLE;
        writew(val, gpt_base + CR(CLKEVT));

        break;
    case CLOCK_EVT_MODE_ONESHOT:
        val = readw(gpt_base + CR(CLKEVT));
        val |= CTRL_ONE_SHOT;
        writew(val, gpt_base + CR(CLKEVT));

        break;
    case CLOCK_EVT_MODE_UNUSED:
    case CLOCK_EVT_MODE_SHUTDOWN:
    case CLOCK_EVT_MODE_RESUME:

        break;
    default:
        pr_err("Invalid mode requested\n");
        break;
    }
}

static int clockevent_next_event(unsigned long cycles,
                 struct clock_event_device *clk_event_dev)
{
    u16 val = readw(gpt_base + CR(CLKEVT));

    if (val & CTRL_ENABLE)
        writew(val & ~CTRL_ENABLE, gpt_base + CR(CLKEVT));

    writew(cycles, gpt_base + LOAD(CLKEVT));

    val |= CTRL_ENABLE | CTRL_INT_ENABLE;
    writew(val, gpt_base + CR(CLKEVT));

    return 0;
}

static irqreturn_t spear_timer_interrupt(int irq, void *dev_id)
{
    struct clock_event_device *evt = &clkevt;

    writew(INT_STATUS, gpt_base + IR(CLKEVT));

    evt->event_handler(evt);

    return IRQ_HANDLED;
}

static struct irqaction spear_timer_irq = {
    .name = "timer",
    .flags = IRQF_DISABLED | IRQF_TIMER,
    .handler = spear_timer_interrupt
};

static void __init spear_clockevent_init(int irq)
{
    u32 tick_rate;

    /* program the prescaler */
    writew(CTRL_PRESCALER16, gpt_base + CR(CLKEVT));

    tick_rate = clk_get_rate(gpt_clk);
    tick_rate >>= CTRL_PRESCALER16;

    clockevents_calc_mult_shift(&clkevt, tick_rate, SPEAR_MIN_RANGE);

    clkevt.max_delta_ns = clockevent_delta2ns(0xfff0,
            &clkevt);
    clkevt.min_delta_ns = clockevent_delta2ns(3, &clkevt);

    clkevt.cpumask = cpumask_of(0);

    clockevents_register_device(&clkevt);

    setup_irq(irq, &spear_timer_irq);
}

const static struct of_device_id timer_of_match[] __initconst = {
    { .compatible = "st,spear-timer", },
    { },
};

void __init spear_setup_of_timer(void)
{
    struct device_node *np;
    int irq, ret;

    np = of_find_matching_node(NULL, timer_of_match);
    if (!np) {
        pr_err("%s: No timer passed via DT\n", __func__);
        return;
    }

    irq = irq_of_parse_and_map(np, 0);
    if (!irq) {
        pr_err("%s: No irq passed for timer via DT\n", __func__);
        return;
    }

    gpt_base = of_iomap(np, 0);
    if (!gpt_base) {
        pr_err("%s: of iomap failed\n", __func__);
        return;
    }

    gpt_clk = clk_get_sys("gpt0", NULL);
    if (!gpt_clk) {
        pr_err("%s:couldn't get clk for gpt\n", __func__);
        goto err_iomap;
    }

    ret = clk_prepare_enable(gpt_clk);
    if (ret < 0) {
        pr_err("%s:couldn't prepare-enable gpt clock\n", __func__);
        goto err_prepare_enable_clk;
    }

    spear_clockevent_init(irq);
    spear_clocksource_init();

    return;

err_prepare_enable_clk:
    clk_put(gpt_clk);
err_iomap:
    iounmap(gpt_base);
}