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/*
* at91sam926x_time.c - Periodic Interval Timer (PIT) for at91sam926x
*
* Copyright (C) 2005-2006 M. Amine SAYA, ATMEL Rousset, France
* Revision 2005 M. Nicolas Diremdjian, ATMEL Rousset, France
* Converted to ClockSource/ClockEvents by David Brownell.
*
* 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/interrupt.h>
#include <linux/irq.h>
#include <linux/kernel.h>
#include <linux/clk.h>
#include <linux/clockchips.h>
#include <asm/mach/time.h>
#include <mach/at91_pit.h>
#define PIT_CPIV(x) ((x) & AT91_PIT_CPIV)
#define PIT_PICNT(x) (((x) & AT91_PIT_PICNT) >> 20)
static u32 pit_cycle; /* write-once */
static u32 pit_cnt; /* access only w/system irq blocked */
/*
* Clocksource: just a monotonic counter of MCK/16 cycles.
* We don't care whether or not PIT irqs are enabled.
*/
static cycle_t read_pit_clk(struct clocksource *cs)
{
unsigned long flags;
u32 elapsed;
u32 t;
raw_local_irq_save(flags);
elapsed = pit_cnt;
t = at91_sys_read(AT91_PIT_PIIR);
raw_local_irq_restore(flags);
elapsed += PIT_PICNT(t) * pit_cycle;
elapsed += PIT_CPIV(t);
return elapsed;
}
static struct clocksource pit_clk = {
.name = "pit",
.rating = 175,
.read = read_pit_clk,
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
};
/*
* Clockevent device: interrupts every 1/HZ (== pit_cycles * MCK/16)
*/
static void
pit_clkevt_mode(enum clock_event_mode mode, struct clock_event_device *dev)
{
switch (mode) {
case CLOCK_EVT_MODE_PERIODIC:
/* update clocksource counter */
pit_cnt += pit_cycle * PIT_PICNT(at91_sys_read(AT91_PIT_PIVR));
at91_sys_write(AT91_PIT_MR, (pit_cycle - 1) | AT91_PIT_PITEN
| AT91_PIT_PITIEN);
break;
case CLOCK_EVT_MODE_ONESHOT:
BUG();
/* FALLTHROUGH */
case CLOCK_EVT_MODE_SHUTDOWN:
case CLOCK_EVT_MODE_UNUSED:
/* disable irq, leaving the clocksource active */
at91_sys_write(AT91_PIT_MR, (pit_cycle - 1) | AT91_PIT_PITEN);
break;
case CLOCK_EVT_MODE_RESUME:
break;
}
}
static struct clock_event_device pit_clkevt = {
.name = "pit",
.features = CLOCK_EVT_FEAT_PERIODIC,
.shift = 32,
.rating = 100,
.set_mode = pit_clkevt_mode,
};
/*
* IRQ handler for the timer.
*/
static irqreturn_t at91sam926x_pit_interrupt(int irq, void *dev_id)
{
/*
* 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());
/* The PIT interrupt may be disabled, and is shared */
if ((pit_clkevt.mode == CLOCK_EVT_MODE_PERIODIC)
&& (at91_sys_read(AT91_PIT_SR) & AT91_PIT_PITS)) {
unsigned nr_ticks;
/* Get number of ticks performed before irq, and ack it */
nr_ticks = PIT_PICNT(at91_sys_read(AT91_PIT_PIVR));
do {
pit_cnt += pit_cycle;
pit_clkevt.event_handler(&pit_clkevt);
nr_ticks--;
} while (nr_ticks);
return IRQ_HANDLED;
}
return IRQ_NONE;
}
static struct irqaction at91sam926x_pit_irq = {
.name = "at91_tick",
.flags = IRQF_SHARED | IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
.handler = at91sam926x_pit_interrupt
};
static void at91sam926x_pit_reset(void)
{
/* Disable timer and irqs */
at91_sys_write(AT91_PIT_MR, 0);
/* Clear any pending interrupts, wait for PIT to stop counting */
while (PIT_CPIV(at91_sys_read(AT91_PIT_PIVR)) != 0)
cpu_relax();
/* Start PIT but don't enable IRQ */
at91_sys_write(AT91_PIT_MR, (pit_cycle - 1) | AT91_PIT_PITEN);
}
/*
* Set up both clocksource and clockevent support.
*/
static void __init at91sam926x_pit_init(void)
{
unsigned long pit_rate;
unsigned bits;
/*
* Use our actual MCK to figure out how many MCK/16 ticks per
* 1/HZ period (instead of a compile-time constant LATCH).
*/
pit_rate = clk_get_rate(clk_get(NULL, "mck")) / 16;
pit_cycle = (pit_rate + HZ/2) / HZ;
WARN_ON(((pit_cycle - 1) & ~AT91_PIT_PIV) != 0);
/* Initialize and enable the timer */
at91sam926x_pit_reset();
/*
* Register clocksource. The high order bits of PIV are unused,
* so this isn't a 32-bit counter unless we get clockevent irqs.
*/
bits = 12 /* PICNT */ + ilog2(pit_cycle) /* PIV */;
pit_clk.mask = CLOCKSOURCE_MASK(bits);
clocksource_register_hz(&pit_clk, pit_rate);
/* Set up irq handler */
setup_irq(AT91_ID_SYS, &at91sam926x_pit_irq);
/* Set up and register clockevents */
pit_clkevt.mult = div_sc(pit_rate, NSEC_PER_SEC, pit_clkevt.shift);
pit_clkevt.cpumask = cpumask_of(0);
clockevents_register_device(&pit_clkevt);
}
static void at91sam926x_pit_suspend(void)
{
/* Disable timer */
at91_sys_write(AT91_PIT_MR, 0);
}
struct sys_timer at91sam926x_timer = {
.init = at91sam926x_pit_init,
.suspend = at91sam926x_pit_suspend,
.resume = at91sam926x_pit_reset,
};
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