OpenRISC: Timekeeping

Implements support for the OpenRISC timer which is a 28 bit cycle counter
that can be read out of a special purpose register.  This counter is
used as a both a clock event and clocksource device.
Signed-off-by: Jonas Bonn <jonas@southpole.se>
Cc: tglx@linutronix.de
Reviewed-by: Arnd Bergmann <arnd@arndb.de>

arch/openrisc/include/asm/timex.h

+/*
+ * OpenRISC Linux
+ *
+ * Linux architectural port borrowing liberally from similar works of
+ * others.  All original copyrights apply as per the original source
+ * declaration.
+ *
+ * OpenRISC implementation:
+ * Copyright (C) 2010-2011 Jonas Bonn <jonas@southpole.se>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#ifndef __ASM_OPENRISC_TIMEX_H
+#define __ASM_OPENRISC_TIMEX_H
+
+#define get_cycles get_cycles
+
+#include <asm-generic/timex.h>
+#include <asm/spr.h>
+#include <asm/spr_defs.h>
+
+static inline cycles_t get_cycles(void)
+{
+	return mfspr(SPR_TTCR);
+}
+
+/* This isn't really used any more */
+#define CLOCK_TICK_RATE 1000
+
+#define ARCH_HAS_READ_CURRENT_TIMER
+
+#endif

arch/openrisc/kernel/time.c

+/*
+ * OpenRISC time.c
+ *
+ * Linux architectural port borrowing liberally from similar works of
+ * others.  All original copyrights apply as per the original source
+ * declaration.
+ *
+ * Modifications for the OpenRISC architecture:
+ * Copyright (C) 2010-2011 Jonas Bonn <jonas@southpole.se>
+ *
+ *      This program is free software; you can redistribute it and/or
+ *      modify it under the terms of the GNU General Public License
+ *      as published by the Free Software Foundation; either version
+ *      2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/kernel.h>
+#include <linux/time.h>
+#include <linux/timex.h>
+#include <linux/interrupt.h>
+#include <linux/ftrace.h>
+
+#include <linux/clocksource.h>
+#include <linux/clockchips.h>
+#include <linux/irq.h>
+#include <linux/io.h>
+
+#include <asm/cpuinfo.h>
+
+static int openrisc_timer_set_next_event(unsigned long delta,
+					 struct clock_event_device *dev)
+{
+	u32 c;
+
+	/* Read 32-bit counter value, add delta, mask off the low 28 bits.
+	 * We're guaranteed delta won't be bigger than 28 bits because the
+	 * generic timekeeping code ensures that for us.
+	 */
+	c = mfspr(SPR_TTCR);
+	c += delta;
+	c &= SPR_TTMR_TP;
+
+	/* Set counter and enable interrupt.
+	 * Keep timer in continuous mode always.
+	 */
+	mtspr(SPR_TTMR, SPR_TTMR_CR | SPR_TTMR_IE | c);
+
+	return 0;
+}
+
+static void openrisc_timer_set_mode(enum clock_event_mode mode,
+				    struct clock_event_device *evt)
+{
+	switch (mode) {
+	case CLOCK_EVT_MODE_PERIODIC:
+		pr_debug(KERN_INFO "%s: periodic\n", __func__);
+		BUG();
+		break;
+	case CLOCK_EVT_MODE_ONESHOT:
+		pr_debug(KERN_INFO "%s: oneshot\n", __func__);
+		break;
+	case CLOCK_EVT_MODE_UNUSED:
+		pr_debug(KERN_INFO "%s: unused\n", __func__);
+		break;
+	case CLOCK_EVT_MODE_SHUTDOWN:
+		pr_debug(KERN_INFO "%s: shutdown\n", __func__);
+		break;
+	case CLOCK_EVT_MODE_RESUME:
+		pr_debug(KERN_INFO "%s: resume\n", __func__);
+		break;
+	}
+}
+
+/* This is the clock event device based on the OR1K tick timer.
+ * As the timer is being used as a continuous clock-source (required for HR
+ * timers) we cannot enable the PERIODIC feature.  The tick timer can run using
+ * one-shot events, so no problem.
+ */
+
+static struct clock_event_device clockevent_openrisc_timer = {
+	.name = "openrisc_timer_clockevent",
+	.features = CLOCK_EVT_FEAT_ONESHOT,
+	.rating = 300,
+	.set_next_event = openrisc_timer_set_next_event,
+	.set_mode = openrisc_timer_set_mode,
+};
+
+static inline void timer_ack(void)
+{
+	/* Clear the IP bit and disable further interrupts */
+	/* This can be done very simply... we just need to keep the timer
+	   running, so just maintain the CR bits while clearing the rest
+	   of the register
+	 */
+	mtspr(SPR_TTMR, SPR_TTMR_CR);
+}
+
+/*
+ * The timer interrupt is mostly handled in generic code nowadays... this
+ * function just acknowledges the interrupt and fires the event handler that
+ * has been set on the clockevent device by the generic time management code.
+ *
+ * This function needs to be called by the timer exception handler and that's
+ * all the exception handler needs to do.
+ */
+
+irqreturn_t __irq_entry timer_interrupt(struct pt_regs *regs)
+{
+	struct pt_regs *old_regs = set_irq_regs(regs);
+	struct clock_event_device *evt = &clockevent_openrisc_timer;
+
+	timer_ack();
+
+	/*
+	 * update_process_times() expects us to have called irq_enter().
+	 */
+	irq_enter();
+	evt->event_handler(evt);
+	irq_exit();
+
+	set_irq_regs(old_regs);
+
+	return IRQ_HANDLED;
+}
+
+static __init void openrisc_clockevent_init(void)
+{
+	clockevents_calc_mult_shift(&clockevent_openrisc_timer,
+				    cpuinfo.clock_frequency, 4);
+
+	/* We only have 28 bits */
+	clockevent_openrisc_timer.max_delta_ns =
+	    clockevent_delta2ns((u32) 0x0fffffff, &clockevent_openrisc_timer);
+	clockevent_openrisc_timer.min_delta_ns =
+	    clockevent_delta2ns(1, &clockevent_openrisc_timer);
+	clockevent_openrisc_timer.cpumask = cpumask_of(0);
+	clockevents_register_device(&clockevent_openrisc_timer);
+}
+
+/**
+ * Clocksource: Based on OpenRISC timer/counter
+ *
+ * This sets up the OpenRISC Tick Timer as a clock source.  The tick timer
+ * is 32 bits wide and runs at the CPU clock frequency.
+ */
+
+static cycle_t openrisc_timer_read(struct clocksource *cs)
+{
+	return (cycle_t) mfspr(SPR_TTCR);
+}
+
+static struct clocksource openrisc_timer = {
+	.name = "openrisc_timer",
+	.rating = 200,
+	.read = openrisc_timer_read,
+	.mask = CLOCKSOURCE_MASK(32),
+	.flags = CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
+static int __init openrisc_timer_init(void)
+{
+	if (clocksource_register_hz(&openrisc_timer, cpuinfo.clock_frequency))
+		panic("failed to register clocksource");
+
+	/* Enable the incrementer: 'continuous' mode with interrupt disabled */
+	mtspr(SPR_TTMR, SPR_TTMR_CR);
+
+	return 0;
+}
+
+void __init time_init(void)
+{
+	u32 upr;
+
+	upr = mfspr(SPR_UPR);
+	if (!(upr & SPR_UPR_TTP))
+		panic("Linux not supported on devices without tick timer");
+
+	openrisc_timer_init();
+	openrisc_clockevent_init();
+}