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[ARM] 4989/1: [AT91] SAM9 ClockSource / ClockEvents
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Update AT91SAM9/CAP9 PIT driver to use generic time and clockevent
infrastructure:

 - Clocksource gives sub-microsecond timestamp precision, assuming
 memory is clocked at over 16 MHz.  It's less than a 32 bit counter,
 unless it's is also generating IRQs.

 - Clockevent device supports periodic mode only; no oneshot
 support from this hardware.  No IRQs generated unless it's the
 active clocksource.

Later, another timer (probably from a TC module) can provide a oneshot
clockevent device to get NO_HZ and High-Res-Timer behavior.

This also updates the timekeeping to use the actual master clock rate
on the system, instead of compile-time <asm/arch/timex.h> constants
matching what Atmel's EK boards use.  (Product boards may well differ!)

Plus cleanup:  rename "*_timer*" symbols to "*_pit*" (there are other
timers, but only one PIT); shorter lines; remove needless CPP stuff;
make several symbols static; etc.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Victor <linux@maxim.org.za>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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Andrew Victor authored and Russell King committed Apr 17, 2008
1 parent 11aadac commit ad48ce7
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Showing 2 changed files with 135 additions and 46 deletions.
10 changes: 10 additions & 0 deletions arch/arm/mach-at91/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -12,18 +12,28 @@ config ARCH_AT91RM9200

config ARCH_AT91SAM9260
bool "AT91SAM9260 or AT91SAM9XE"
select GENERIC_TIME
select GENERIC_CLOCKEVENTS

config ARCH_AT91SAM9261
bool "AT91SAM9261"
select GENERIC_TIME
select GENERIC_CLOCKEVENTS

config ARCH_AT91SAM9263
bool "AT91SAM9263"
select GENERIC_TIME
select GENERIC_CLOCKEVENTS

config ARCH_AT91SAM9RL
bool "AT91SAM9RL"
select GENERIC_TIME
select GENERIC_CLOCKEVENTS

config ARCH_AT91CAP9
bool "AT91CAP9"
select GENERIC_TIME
select GENERIC_CLOCKEVENTS

config ARCH_AT91X40
bool "AT91x40"
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171 changes: 125 additions & 46 deletions arch/arm/mach-at91/at91sam926x_time.c
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Original file line number Diff line number Diff line change
@@ -1,23 +1,20 @@
/*
* linux/arch/arm/mach-at91/at91sam926x_time.c
* 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/init.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/time.h>
#include <linux/clk.h>
#include <linux/clockchips.h>

#include <asm/hardware.h>
#include <asm/io.h>
#include <asm/mach/time.h>

#include <asm/arch/at91_pit.h>
Expand All @@ -26,85 +23,167 @@
#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 */


/*
* Returns number of microseconds since last timer interrupt. Note that interrupts
* will have been disabled by do_gettimeofday()
* 'LATCH' is hwclock ticks (see CLOCK_TICK_RATE in timex.h) per jiffy.
* Clocksource: just a monotonic counter of MCK/16 cycles.
* We don't care whether or not PIT irqs are enabled.
*/
static unsigned long at91sam926x_gettimeoffset(void)
static cycle_t read_pit_clk(void)
{
unsigned long elapsed;
unsigned long t = at91_sys_read(AT91_PIT_PIIR);
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,
.shift = 20,
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
};

elapsed = (PIT_PICNT(t) * LATCH) + PIT_CPIV(t); /* hardware clock cycles */

return (unsigned long)(elapsed * jiffies_to_usecs(1)) / LATCH;
/*
* 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)
{
unsigned long flags;

switch (mode) {
case CLOCK_EVT_MODE_PERIODIC:
/* update clocksource counter, then enable the IRQ */
raw_local_irq_save(flags);
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);
raw_local_irq_restore(flags);
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,
.cpumask = CPU_MASK_CPU0,
.set_mode = pit_clkevt_mode,
};


/*
* IRQ handler for the timer.
*/
static irqreturn_t at91sam926x_timer_interrupt(int irq, void *dev_id)
static irqreturn_t at91sam926x_pit_interrupt(int irq, void *dev_id)
{
volatile long nr_ticks;

if (at91_sys_read(AT91_PIT_SR) & AT91_PIT_PITS) { /* This is a shared interrupt */
/* Get number to ticks performed before interrupt and clear PIT interrupt */
/* 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 {
timer_tick();
pit_cnt += pit_cycle;
pit_clkevt.event_handler(&pit_clkevt);
nr_ticks--;
} while (nr_ticks);

return IRQ_HANDLED;
} else
return IRQ_NONE; /* not handled */
}

return IRQ_NONE;
}

static struct irqaction at91sam926x_timer_irq = {
static struct irqaction at91sam926x_pit_irq = {
.name = "at91_tick",
.flags = IRQF_SHARED | IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
.handler = at91sam926x_timer_interrupt
.handler = at91sam926x_pit_interrupt
};

void at91sam926x_timer_reset(void)
static void at91sam926x_pit_reset(void)
{
/* Disable timer */
/* Disable timer and irqs */
at91_sys_write(AT91_PIT_MR, 0);

/* Clear any pending interrupts */
(void) at91_sys_read(AT91_PIT_PIVR);
/* Clear any pending interrupts, wait for PIT to stop counting */
while (PIT_CPIV(at91_sys_read(AT91_PIT_PIVR)) != 0)
cpu_relax();

/* Set Period Interval timer and enable its interrupt */
at91_sys_write(AT91_PIT_MR, (LATCH & AT91_PIT_PIV) | AT91_PIT_PITIEN | AT91_PIT_PITEN);
/* Start PIT but don't enable IRQ */
at91_sys_write(AT91_PIT_MR, (pit_cycle - 1) | AT91_PIT_PITEN);
}

/*
* Set up timer interrupt.
* Set up both clocksource and clockevent support.
*/
void __init at91sam926x_timer_init(void)
static void __init at91sam926x_pit_init(void)
{
/* Initialize and enable the timer */
at91sam926x_timer_reset();
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);

/* Make IRQs happen for the system timer. */
setup_irq(AT91_ID_SYS, &at91sam926x_timer_irq);
/* 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.
*/
pit_clk.mult = clocksource_hz2mult(pit_rate, pit_clk.shift);
bits = 12 /* PICNT */ + ilog2(pit_cycle) /* PIV */;
pit_clk.mask = CLOCKSOURCE_MASK(bits);
clocksource_register(&pit_clk);

/* 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);
clockevents_register_device(&pit_clkevt);
}

#ifdef CONFIG_PM
static void at91sam926x_timer_suspend(void)
static void at91sam926x_pit_suspend(void)
{
/* Disable timer */
at91_sys_write(AT91_PIT_MR, 0);
}
#else
#define at91sam926x_timer_suspend NULL
#endif

struct sys_timer at91sam926x_timer = {
.init = at91sam926x_timer_init,
.offset = at91sam926x_gettimeoffset,
.suspend = at91sam926x_timer_suspend,
.resume = at91sam926x_timer_reset,
.init = at91sam926x_pit_init,
.suspend = at91sam926x_pit_suspend,
.resume = at91sam926x_pit_reset,
};

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