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>

2 files changed, 217 insertions, 0 deletions

diff --git a/arch/openrisc/include/asm/timex.h b/arch/openrisc/include/asm/timex.h
new file mode 100644
index 000000000000..9935cad1b9b9
--- /dev/null
+++ b/arch/openrisc/include/asm/timex.h
@@ -0,0 +1,36 @@
+/*
+ * 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
diff --git a/arch/openrisc/kernel/time.c b/arch/openrisc/kernel/time.c
new file mode 100644
index 000000000000..bd946ef1623d
--- /dev/null
+++ b/arch/openrisc/kernel/time.c
@@ -0,0 +1,181 @@
+/*
+ * 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();
+}