alistair23-linux/arch/arm/mach-pxa/time.c

/*
 * arch/arm/mach-pxa/time.c
 *
 * Author:	Nicolas Pitre
 * Created:	Jun 15, 2001
 * Copyright:	MontaVista Software Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/interrupt.h>
#include <linux/time.h>
#include <linux/signal.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/clocksource.h>

#include <asm/system.h>
#include <asm/hardware.h>
#include <asm/io.h>
#include <asm/leds.h>
#include <asm/irq.h>
#include <asm/mach/irq.h>
#include <asm/mach/time.h>
#include <asm/arch/pxa-regs.h>


static int pxa_set_rtc(void)
{
	unsigned long current_time = xtime.tv_sec;

	if (RTSR & RTSR_ALE) {
		/* make sure not to forward the clock over an alarm */
		unsigned long alarm = RTAR;
		if (current_time >= alarm && alarm >= RCNR)
			return -ERESTARTSYS;
	}
	RCNR = current_time;
	return 0;
}

#ifdef CONFIG_NO_IDLE_HZ
static unsigned long initial_match;
static int match_posponed;
#endif

static irqreturn_t
pxa_timer_interrupt(int irq, void *dev_id)
{
	int next_match;

	write_seqlock(&xtime_lock);

#ifdef CONFIG_NO_IDLE_HZ
	if (match_posponed) {
		match_posponed = 0;
		OSMR0 = initial_match;
	}
#endif

	/* Loop until we get ahead of the free running timer.
	 * This ensures an exact clock tick count and time accuracy.
	 * Since IRQs are disabled at this point, coherence between
	 * lost_ticks(updated in do_timer()) and the match reg value is
	 * ensured, hence we can use do_gettimeofday() from interrupt
	 * handlers.
	 *
	 * HACK ALERT: it seems that the PXA timer regs aren't updated right
	 * away in all cases when a write occurs.  We therefore compare with
	 * 8 instead of 0 in the while() condition below to avoid missing a
	 * match if OSCR has already reached the next OSMR value.
	 * Experience has shown that up to 6 ticks are needed to work around
	 * this problem, but let's use 8 to be conservative.  Note that this
	 * affect things only when the timer IRQ has been delayed by nearly
	 * exactly one tick period which should be a pretty rare event.
	 */
	do {
		timer_tick();
		OSSR = OSSR_M0;  /* Clear match on timer 0 */
		next_match = (OSMR0 += LATCH);
	} while( (signed long)(next_match - OSCR) <= 8 );

	write_sequnlock(&xtime_lock);

	return IRQ_HANDLED;
}

static struct irqaction pxa_timer_irq = {
	.name		= "PXA Timer Tick",
	.flags		= IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
	.handler	= pxa_timer_interrupt,
};

static cycle_t pxa_get_cycles(void)
{
	return OSCR;
}

static struct clocksource clocksource_pxa = {
	.name           = "pxa_timer",
	.rating         = 200,
	.read           = pxa_get_cycles,
	.mask           = CLOCKSOURCE_MASK(32),
	.shift          = 20,
	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
};

static void __init pxa_timer_init(void)
{
	struct timespec tv;
	unsigned long flags;

	set_rtc = pxa_set_rtc;

	OIER = 0;		/* disable any timer interrupts */
	OSSR = 0xf;		/* clear status on all timers */
	setup_irq(IRQ_OST0, &pxa_timer_irq);
	local_irq_save(flags);
	OIER = OIER_E0;		/* enable match on timer 0 to cause interrupts */
	OSMR0 = OSCR + LATCH;	/* set initial match */
	local_irq_restore(flags);

	/*
	 * OSCR runs continuously on PXA and is not written to,
	 * so we can use it as clock source directly.
	 */
	clocksource_pxa.mult =
		clocksource_hz2mult(CLOCK_TICK_RATE, clocksource_pxa.shift);
	clocksource_register(&clocksource_pxa);
}

#ifdef CONFIG_NO_IDLE_HZ
static int pxa_dyn_tick_enable_disable(void)
{
	/* nothing to do */
	return 0;
}

static void pxa_dyn_tick_reprogram(unsigned long ticks)
{
	if (ticks > 1) {
		initial_match = OSMR0;
		OSMR0 = initial_match + ticks * LATCH;
		match_posponed = 1;
	}
}

static irqreturn_t
pxa_dyn_tick_handler(int irq, void *dev_id)
{
	if (match_posponed) {
		match_posponed = 0;
		OSMR0 = initial_match;
		if ( (signed long)(initial_match - OSCR) <= 8 )
			return pxa_timer_interrupt(irq, dev_id);
	}
	return IRQ_NONE;
}

static struct dyn_tick_timer pxa_dyn_tick = {
	.enable		= pxa_dyn_tick_enable_disable,
	.disable	= pxa_dyn_tick_enable_disable,
	.reprogram	= pxa_dyn_tick_reprogram,
	.handler	= pxa_dyn_tick_handler,
};
#endif

#ifdef CONFIG_PM
static unsigned long osmr[4], oier;

static void pxa_timer_suspend(void)
{
	osmr[0] = OSMR0;
	osmr[1] = OSMR1;
	osmr[2] = OSMR2;
	osmr[3] = OSMR3;
	oier = OIER;
}

static void pxa_timer_resume(void)
{
	OSMR0 = osmr[0];
	OSMR1 = osmr[1];
	OSMR2 = osmr[2];
	OSMR3 = osmr[3];
	OIER = oier;

	/*
	 * OSMR0 is the system timer: make sure OSCR is sufficiently behind
	 */
	OSCR = OSMR0 - LATCH;
}
#else
#define pxa_timer_suspend NULL
#define pxa_timer_resume NULL
#endif

struct sys_timer pxa_timer = {
	.init		= pxa_timer_init,
	.suspend	= pxa_timer_suspend,
	.resume		= pxa_timer_resume,
#ifdef CONFIG_NO_IDLE_HZ
	.dyn_tick	= &pxa_dyn_tick,
#endif
};