Hello all,
I have taken a stab at implementing a clocksource and a event device on
my AT91SAM9260. I based it on David Brownell's work on the 9200. I would
love some feedback as I'm not confident I have everything right.
Specifically:
- I'm not sure how to pick the .shift member of struct clocksource. It
seems that it would be based on the register size, but it's not clear to
me.
- More importantly, I do not get a dyn_tick file in
the /sys/devices/system/timer/timer0 directory and can't seem to turn on
the feature even with dyntick=enable in the kernel parameters. Have I
missed something in the driver?
Kindly CC me on any responses as currently I only read the archives.
Signed-off-by: Andrew J. Herzig <[email protected]>
---
arch/arm/Kconfig | 2
arch/arm/mach-at91/at91sam926x_time.c | 225 ++++++++++++++++++------ 2
files changed, 176 insertions(+), 51 deletions(-)
diff -uprN -X linux-2.6.23-rc2-vanilla/Documentation/dontdiff
linux-2.6.23-rc2-vanilla/arch/arm/Kconfig
linux-2.6.23-rc2-testpatch/arch/arm/Kconfig
--- linux-2.6.23-rc2-vanilla/arch/arm/Kconfig 2007-08-08
13:28:38.000000000 -0400
+++ linux-2.6.23-rc2-testpatch/arch/arm/Kconfig 2007-08-08
15:17:15.000000000 -0400
@@ -179,6 +179,8 @@ config ARCH_VERSATILE
config ARCH_AT91
bool "Atmel AT91"
select GENERIC_GPIO
+ select GENERIC_TIME
+ select GENERIC_CLOCKEVENTS
help
This enables support for systems based on the Atmel AT91RM9200
and AT91SAM9xxx processors.
diff -uprN -X linux-2.6.23-rc2-vanilla/Documentation/dontdiff
linux-2.6.23-rc2-vanilla/arch/arm/mach-at91/at91sam926x_time.c
linux-2.6.23-rc2-testpatch/arch/arm/mach-at91/at91sam926x_time.c
--- linux-2.6.23-rc2-vanilla/arch/arm/mach-at91/at91sam926x_time.c
2007-08-08 13:28:37.000000000 -0400
+++ linux-2.6.23-rc2-testpatch/arch/arm/mach-at91/at91sam926x_time.c
2007-08-08 15:16:15.000000000 -0400
@@ -1,44 +1,57 @@
/*
* linux/arch/arm/mach-at91/at91sam926x_time.c
*
- * Copyright (C) 2005-2006 M. Amine SAYA, ATMEL Rousset, France
- * Revision 2005 M. Nicolas Diremdjian, ATMEL Rousset, France
+ * clockevents and clocksource implementation based on a compination
+ * of the PIT and RTT system hardware.
+ * Copyright (c) 2007 Andrew J. Herzig <[email protected]>.
+ *
+ * Derived largely from David Brownell's implementation for the RM9200.
*
* 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/clockchips.h>
#include <asm/hardware.h>
#include <asm/io.h>
#include <asm/mach/time.h>
-
#include <asm/arch/at91_pit.h>
+#include <asm/arch/at91_rtt.h>
+static struct clock_event_device clkevt;
-#define PIT_CPIV(x) ((x) & AT91_PIT_CPIV)
-#define PIT_PICNT(x) (((x) & AT91_PIT_PICNT) >> 20)
+/* According to 6221D–ATARM–12-Mar-07 p.103, the status register
+ * is cleared 2 SLOW_CLOCK cycles after a read. Therefore, to avoid
+ * a race, we must wait for the register to actually clear before
+ * re-enabling interrupts. If there's a better fix for this, I don't
+ * know it.
+ */
+static inline void clear_RTT_SR(void)
+{
+ while (at91_sys_read(AT91_RTT_SR))
+ ;
+}
/*
- * 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.
+ * The counter value (CRTV) is updated asychronously to the master
+ * clock, so we are advised to read RTT_VR twice to avoid glitching.
*/
-static unsigned long at91sam926x_gettimeoffset(void)
+static inline unsigned long read_CRTV(void)
{
- unsigned long elapsed;
- unsigned long t = at91_sys_read(AT91_PIT_PIIR);
+ unsigned long x1, x2;
- elapsed = (PIT_PICNT(t) * LATCH) + PIT_CPIV(t); /*
hardware clock cycles */
-
- return (unsigned long)(elapsed * jiffies_to_usecs(1)) / LATCH;
+ x1 = at91_sys_read(AT91_RTT_VR);
+ while (1) {
+ x2 = at91_sys_read(AT91_RTT_VR);
+ if (x1 == x2)
+ break;
+ x1 = x2;
+ }
+ return x1;
}
/*
@@ -48,66 +61,176 @@ static irqreturn_t at91sam926x_timer_int
{
volatile long nr_ticks;
- if (at91_sys_read(AT91_PIT_SR) & AT91_PIT_PITS) { /* This
is a shared interrupt */
- write_seqlock(&xtime_lock);
+ /* Periodic mode. */
+ if (at91_sys_read(AT91_PIT_SR) & AT91_PIT_PITS) { /* shared
interrupt */
- /* Get number to ticks performed before interrupt and
clear PIT interrupt */
- nr_ticks = PIT_PICNT(at91_sys_read(AT91_PIT_PIVR));
+ /* Get number of system ticks between last interrupt
+ * and now and clear PIT interrupt. This is to support
+ * dynticks.
+ */
+ nr_ticks = (at91_sys_read(AT91_PIT_PIVR) &
AT91_PIT_PICNT)
+ >> 20;
do {
- timer_tick();
+ /* Call evt handler for every sys tick missed.
*/
+ clkevt.event_handler(&clkevt);
nr_ticks--;
} while (nr_ticks);
- write_sequnlock(&xtime_lock);
return IRQ_HANDLED;
- } else
- return IRQ_NONE; /* not handled */
+ }
+
+ /* "Oneshot" timer (alarm mode). */
+ if (at91_sys_read(AT91_RTT_SR) & AT91_RTT_ALMS) {
+ clear_RTT_SR();
+ clkevt.event_handler(&clkevt);
+ return IRQ_HANDLED;
+ }
+ return IRQ_NONE; /* not handled, this IRQ is
shared */
}
static struct irqaction at91sam926x_timer_irq = {
- .name = "at91_tick",
- .flags = IRQF_SHARED | IRQF_DISABLED | IRQF_TIMER |
IRQF_IRQPOLL,
- .handler = at91sam926x_timer_interrupt
+ .name = "at91_tick",
+ .flags = IRQF_SHARED | IRQF_DISABLED
+ | IRQF_TIMER | IRQF_IRQPOLL,
+ .handler = at91sam926x_timer_interrupt
+};
+
+static cycle_t read_clksrc(void)
+{
+ return read_CRTV();
+}
+
+static struct clocksource clksrc = {
+ .name = "at91_rtt",
+ .rating = 150,
+ .read = read_clksrc,
+ .mask = CLOCKSOURCE_MASK(32),
+ .shift = 10,
+ .flags = CLOCK_SOURCE_IS_CONTINUOUS,
};
-void at91sam926x_timer_reset(void)
+#ifdef CONFIG_PM
+
+static void at91sam926x_timer_suspend(void)
+{
+ printk(KERN_ALERT "926x_timer_suspend\n");
+ /* Disable both PIT and RTT counters. */
+ at91_sys_write(AT91_PIT_MR, 0);
+ at91_sys_write(AT91_RTT_MR, 0);
+}
+
+static void at91sam926x_timer_resume(void)
+{
+ printk(KERN_ALERT "926x_timer_resume\n");
+ at91_sys_write(AT91_RTT_MR, 1 | AT91_RTT_RTTRST);
+ at91_sys_write(AT91_PIT_MR, (LATCH & AT91_PIT_PIV)
+ | AT91_PIT_PITIEN | AT91_PIT_PITEN);
+}
+#else
+#define at91sam926x_timer_suspend NULL
+#define at91sam926x_timer_resume NULL
+#endif
+
+static void
+at91sam926x_timer_mode(enum clock_event_mode mode,
+ struct clock_event_device *dev)
{
- /* Disable timer */
+ /* Disable timer interrupts and clear any pending. */
at91_sys_write(AT91_PIT_MR, 0);
+ at91_sys_read(AT91_PIT_PIVR);
- /* Clear any pending interrupts */
- (void) at91_sys_read(AT91_PIT_PIVR);
+ at91_sys_write(AT91_RTT_MR, 1);
+ clear_RTT_SR();
- /* Set Period Interval timer and enable its interrupt */
- at91_sys_write(AT91_PIT_MR, (LATCH & AT91_PIT_PIV) |
AT91_PIT_PITIEN | AT91_PIT_PITEN);
+ switch(mode) {
+ case CLOCK_EVT_MODE_PERIODIC:
+ /* Standard PIT; period = HZ. */
+ at91_sys_write(AT91_PIT_MR, (LATCH & AT91_PIT_PIV)
+ | AT91_PIT_PITIEN | AT91_PIT_PITEN);
+ break;
+ case CLOCK_EVT_MODE_ONESHOT:
+ /* Oneshot hanled by the RTT hardware.
+ * Set alarm to just missed. Real alarm value will get
+ * set by next_event() before counter rolls back around.
+ */
+ at91_sys_write(AT91_RTT_AR, read_CRTV());
+ at91_sys_write(AT91_RTT_MR, AT91_RTT_ALMIEN | 1);
+ break;
+ case CLOCK_EVT_MODE_SHUTDOWN:
+ at91sam926x_timer_suspend();
+ break;
+ case CLOCK_EVT_MODE_RESUME:
+ at91sam926x_timer_resume();
+ break;
+ case CLOCK_EVT_MODE_UNUSED:
+ break;
+ }
}
+static int at91sam926x_timer_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);
+ alm = read_CRTV();
+
+ /* Cancel any pending alarm; flush any pending IRQ */
+ at91_sys_write(AT91_RTT_AR, alm);
+ clear_RTT_SR();
+
+ /* Schedule alarm by writing to alarm register. */
+ alm += delta;
+ at91_sys_write(AT91_RTT_AR, 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,
+ .cpumask = CPU_MASK_CPU0,
+ .set_next_event = at91sam926x_timer_next_event,
+ .set_mode = at91sam926x_timer_mode,
+};
+
/*
* Set up timer interrupt.
*/
-void __init at91sam926x_timer_init(void)
+static void __init at91sam926x_timer_init(void)
{
- /* Initialize and enable the timer */
- at91sam926x_timer_reset();
+
+ /* Disable interrupts and clear any pending.
+ * The 32 kHz "slow clock" drives the RTT timer. We adjust
+ * the prescaler down to 1 for better resolution. Otherwise
+ * we get a 1 Hz default. This however requires waiting
+ * for the RTT_SR to clear before re-enabling interrupts.
+ */
+ at91_sys_write(AT91_RTT_MR, 1 | AT91_RTT_RTTRST);
+ at91_sys_read(AT91_RTT_SR);
/* Make IRQs happen for the system timer. */
setup_irq(AT91_ID_SYS, &at91sam926x_timer_irq);
+ clkevt.mult = div_sc(AT91_SLOW_CLOCK, NSEC_PER_SEC,
clkevt.shift);
+ clkevt.max_delta_ns = clockevent_delta2ns(AT91_RTT_ALMV,
&clkevt);
+ clkevt.min_delta_ns = clockevent_delta2ns(2, &clkevt) + 1;
+ clockevents_register_device(&clkevt);
+
+ /* Register clocksource. */
+ clksrc.mult = clocksource_hz2mult(AT91_SLOW_CLOCK,
clksrc.shift);
+ clocksource_register(&clksrc);
}
-#ifdef CONFIG_PM
-static void at91sam926x_timer_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,
+ .resume = at91sam926x_timer_resume,
};
-
-
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