sh: dyntick infrastructure.

This adds basic NO_IDLE_HZ support to the SH timer API so timers
are able to wire it up. Taken from the ARM version, as it fit in
to our API with very few changes needed.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/kernel/time.c

@@ -174,6 +174,108 @@ static struct sysdev_class timer_sysclass = {
 	.resume	 = timer_resume,
 };
 
+#ifdef CONFIG_NO_IDLE_HZ
+static int timer_dyn_tick_enable(void)
+{
+	struct dyn_tick_timer *dyn_tick = sys_timer->dyn_tick;
+	unsigned long flags;
+	int ret = -ENODEV;
+
+	if (dyn_tick) {
+		spin_lock_irqsave(&dyn_tick->lock, flags);
+		ret = 0;
+		if (!(dyn_tick->state & DYN_TICK_ENABLED)) {
+			ret = dyn_tick->enable();
+
+			if (ret == 0)
+				dyn_tick->state |= DYN_TICK_ENABLED;
+		}
+		spin_unlock_irqrestore(&dyn_tick->lock, flags);
+	}
+
+	return ret;
+}
+
+static int timer_dyn_tick_disable(void)
+{
+	struct dyn_tick_timer *dyn_tick = sys_timer->dyn_tick;
+	unsigned long flags;
+	int ret = -ENODEV;
+
+	if (dyn_tick) {
+		spin_lock_irqsave(&dyn_tick->lock, flags);
+		ret = 0;
+		if (dyn_tick->state & DYN_TICK_ENABLED) {
+			ret = dyn_tick->disable();
+
+			if (ret == 0)
+				dyn_tick->state &= ~DYN_TICK_ENABLED;
+		}
+		spin_unlock_irqrestore(&dyn_tick->lock, flags);
+	}
+
+	return ret;
+}
+
+/*
+ * Reprogram the system timer for at least the calculated time interval.
+ * This function should be called from the idle thread with IRQs disabled,
+ * immediately before sleeping.
+ */
+void timer_dyn_reprogram(void)
+{
+	struct dyn_tick_timer *dyn_tick = sys_timer->dyn_tick;
+	unsigned long next, seq, flags;
+
+	if (!dyn_tick)
+		return;
+
+	spin_lock_irqsave(&dyn_tick->lock, flags);
+	if (dyn_tick->state & DYN_TICK_ENABLED) {
+		next = next_timer_interrupt();
+		do {
+			seq = read_seqbegin(&xtime_lock);
+			dyn_tick->reprogram(next - jiffies);
+		} while (read_seqretry(&xtime_lock, seq));
+	}
+	spin_unlock_irqrestore(&dyn_tick->lock, flags);
+}
+
+static ssize_t timer_show_dyn_tick(struct sys_device *dev, char *buf)
+{
+	return sprintf(buf, "%i\n",
+		       (sys_timer->dyn_tick->state & DYN_TICK_ENABLED) >> 1);
+}
+
+static ssize_t timer_set_dyn_tick(struct sys_device *dev, const char *buf,
+				  size_t count)
+{
+	unsigned int enable = simple_strtoul(buf, NULL, 2);
+
+	if (enable)
+		timer_dyn_tick_enable();
+	else
+		timer_dyn_tick_disable();
+
+	return count;
+}
+static SYSDEV_ATTR(dyn_tick, 0644, timer_show_dyn_tick, timer_set_dyn_tick);
+
+/*
+ * dyntick=enable|disable
+ */
+static char dyntick_str[4] __initdata = "";
+
+static int __init dyntick_setup(char *str)
+{
+	if (str)
+		strlcpy(dyntick_str, str, sizeof(dyntick_str));
+	return 1;
+}
+
+__setup("dyntick=", dyntick_setup);
+#endif
+
 static int __init timer_init_sysfs(void)
 {
 	int ret = sysdev_class_register(&timer_sysclass);
@@ -181,7 +283,22 @@ static int __init timer_init_sysfs(void)
 		return ret;
 
 	sys_timer->dev.cls = &timer_sysclass;
-	return sysdev_register(&sys_timer->dev);
+	ret = sysdev_register(&sys_timer->dev);
+
+#ifdef CONFIG_NO_IDLE_HZ
+	if (ret == 0 && sys_timer->dyn_tick) {
+		ret = sysdev_create_file(&sys_timer->dev, &attr_dyn_tick);
+
+		/*
+		 * Turn on dynamic tick after calibrate delay
+		 * for correct bogomips
+		 */
+		if (ret == 0 && dyntick_str[0] == 'e')
+			ret = timer_dyn_tick_enable();
+	}
+#endif
+
+	return ret;
 }
 device_initcall(timer_init_sysfs);
 
@@ -205,6 +322,11 @@ void __init time_init(void)
 	sys_timer = get_sys_timer();
 	printk(KERN_INFO "Using %s for system timer\n", sys_timer->name);
 
+#ifdef CONFIG_NO_IDLE_HZ
+	if (sys_timer->dyn_tick)
+		spin_lock_init(&sys_timer->dyn_tick->lock);
+#endif
+
 #if defined(CONFIG_SH_KGDB)
 	/*
 	 * Set up kgdb as requested. We do it here because the serial