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Diffstat (limited to 'arch/arm/mach-at91/at91rm9200_time.c')
-rw-r--r--arch/arm/mach-at91/at91rm9200_time.c211
1 files changed, 211 insertions, 0 deletions
diff --git a/arch/arm/mach-at91/at91rm9200_time.c b/arch/arm/mach-at91/at91rm9200_time.c
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+++ b/arch/arm/mach-at91/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 <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_sys_read(AT91_ST_CRTR);
+ do {
+ x2 = at91_sys_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_sys_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_sys_write(AT91_ST_IDR, AT91_ST_PITS | AT91_ST_ALMS);
+ (void) at91_sys_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_sys_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_sys_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_sys_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_sys_write(AT91_ST_RTAR, alm);
+ (void) at91_sys_read(AT91_ST_SR);
+
+ /* Schedule alarm by writing RTAR. */
+ alm += delta;
+ at91_sys_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,
+};
+
+/*
+ * 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_sys_write(AT91_ST_IDR,
+ AT91_ST_PITS | AT91_ST_WDOVF | AT91_ST_RTTINC | AT91_ST_ALMS);
+ (void) at91_sys_read(AT91_ST_SR);
+
+ /* Make IRQs happen for the system timer */
+ setup_irq(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_sys_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,
+};
+