at91rm9200_time.c

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/*
 * 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/clockchips.h>
#include <linux/export.h>

#include <asm/mach/time.h>

#include <mach/at91_st.h>

static unsigned long last_crtr;
static u32 irqmask;
static struct clock_event_device clkevt;

#define RM9200_TIMER_LATCH  ((AT91_SLOW_CLOCK + HZ/2) / HZ)

/*
 * 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 long x1, x2;

    x1 = at91_st_read(AT91_ST_CRTR);
    do {
        x2 = at91_st_read(AT91_ST_CRTR);
        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 = at91_st_read(AT91_ST_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) >= RM9200_TIMER_LATCH) {
            last_crtr += RM9200_TIMER_LATCH;
            clkevt.event_handler(&clkevt);
        }
        return IRQ_HANDLED;
    }

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

static struct irqaction at91rm9200_timer_irq = {
    .name       = "at91_tick",
    .flags      = IRQF_SHARED | IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
    .handler    = at91rm9200_timer_interrupt
};

static cycle_t 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
clkevt32k_mode(enum clock_event_mode mode, struct clock_event_device *dev)
{
    /* Disable and flush pending timer interrupts */
    at91_st_write(AT91_ST_IDR, AT91_ST_PITS | AT91_ST_ALMS);
    at91_st_read(AT91_ST_SR);

    last_crtr = read_CRTR();
    switch (mode) {
    case CLOCK_EVT_MODE_PERIODIC:
        /* PIT for periodic irqs; fixed rate of 1/HZ */
        irqmask = AT91_ST_PITS;
        at91_st_write(AT91_ST_PIMR, RM9200_TIMER_LATCH);
        break;
    case CLOCK_EVT_MODE_ONESHOT:
        /* ALM for oneshot irqs, set by next_event()
         * before 32 seconds have passed
         */
        irqmask = AT91_ST_ALMS;
        at91_st_write(AT91_ST_RTAR, last_crtr);
        break;
    case CLOCK_EVT_MODE_SHUTDOWN:
    case CLOCK_EVT_MODE_UNUSED:
    case CLOCK_EVT_MODE_RESUME:
        irqmask = 0;
        break;
    }
    at91_st_write(AT91_ST_IER, irqmask);
}

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

    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 */
    at91_st_write(AT91_ST_RTAR, alm);
    at91_st_read(AT91_ST_SR);

    /* Schedule alarm by writing RTAR. */
    alm += delta;
    at91_st_write(AT91_ST_RTAR, alm);

    return status;
}

static struct clock_event_device clkevt = {
    .name       = "at91_tick",
    .features   = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
    .shift      = 32,
    .rating     = 150,
    .set_next_event = clkevt32k_next_event,
    .set_mode   = clkevt32k_mode,
};

void __iomem *at91_st_base;
EXPORT_SYMBOL_GPL(at91_st_base);

void __init at91rm9200_ioremap_st(u32 addr)
{
    at91_st_base = ioremap(addr, 256);
    if (!at91_st_base)
        panic("Impossible to ioremap ST\n");
}

/*
 * ST (system timer) module supports both clockevents and clocksource.
 */
void __init at91rm9200_timer_init(void)
{
    /* Disable all timer interrupts, and clear any pending ones */
    at91_st_write(AT91_ST_IDR,
        AT91_ST_PITS | AT91_ST_WDOVF | AT91_ST_RTTINC | AT91_ST_ALMS);
    at91_st_read(AT91_ST_SR);

    /* Make IRQs happen for the system timer */
    setup_irq(NR_IRQS_LEGACY + AT91_ID_SYS, &at91rm9200_timer_irq);

    /* 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.
     */
    at91_st_write(AT91_ST_RTMR, 1);

    /* Setup timer clockevent, with minimum of two ticks (important!!) */
    clkevt.mult = div_sc(AT91_SLOW_CLOCK, NSEC_PER_SEC, clkevt.shift);
    clkevt.max_delta_ns = clockevent_delta2ns(AT91_ST_ALMV, &clkevt);
    clkevt.min_delta_ns = clockevent_delta2ns(2, &clkevt) + 1;
    clkevt.cpumask = cpumask_of(0);
    clockevents_register_device(&clkevt);

    /* register clocksource */
    clocksource_register_hz(&clk32k, AT91_SLOW_CLOCK);
}

struct sys_timer at91rm9200_timer = {
    .init       = at91rm9200_timer_init,
};