[ARM] 4989/1: [AT91] SAM9 ClockSource / ClockEvents

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>

arch/arm/mach-at91/Kconfig

@@ -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"

arch/arm/mach-at91/at91sam926x_time.c

 /*
- * 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>
@@ -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)
 {
+	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_timer_reset();
+	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);
 
-	/* Make IRQs happen for the system timer. */
-	setup_irq(AT91_ID_SYS, &at91sam926x_timer_irq);
+	/* 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,
 };
-