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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;
/*
* 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;
/* 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) >= LATCH) {
last_crtr += 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(void)
{
return read_CRTR();
}
static struct clocksource clk32k = {
.name = "32k_counter",
.rating = 150,
.read = read_clk32k,
.mask = CLOCKSOURCE_MASK(20),
.shift = 10,
.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, 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)
{
unsigned long flags;
u32 alm;
int status = 0;
BUG_ON(delta < 2);
/* Use "raw" primitives so we behave correctly on RT kernels. */
raw_local_irq_save(flags);
/*
* According to Thomas Gleixner irqs are already disabled here. Simply
* removing raw_local_irq_save above (and the matching
* raw_local_irq_restore) was not accepted. See
* http://thread.gmane.org/gmane.linux.ports.arm.kernel/41174
* So for now (2008-11-20) just warn once if irqs were not disabled ...
*/
WARN_ON_ONCE(!raw_irqs_disabled_flags(flags));
/* 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);
raw_local_irq_restore(flags);
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 */
clk32k.mult = clocksource_hz2mult(AT91_SLOW_CLOCK, clk32k.shift);
clocksource_register(&clk32k);
}
struct sys_timer at91rm9200_timer = {
.init = at91rm9200_timer_init,
};
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