3 files changed, 162 insertions, 1 deletions

diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index 48308dc86e33..aa1ebc561b84 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -423,6 +423,24 @@ config SH_TIMER_IRQ
         default "140" if CPU_SUBTYPE_SH7206
         default "16"
 
+config NO_IDLE_HZ
+        bool "Dynamic tick timer"
+        help
+          Select this option if you want to disable continuous timer ticks
+          and have them programmed to occur as required. This option saves
+          power as the system can remain in idle state for longer.
+
+          By default dynamic tick is disabled during the boot, and can be
+          manually enabled with:
+
+            echo 1 > /sys/devices/system/timer/timer0/dyn_tick
+
+          Alternatively, if you want dynamic tick automatically enabled
+          during boot, pass "dyntick=enable" via the kernel command string.
+
+          Please note that dynamic tick may affect the accuracy of
+          timekeeping on some platforms depending on the implementation.
+
 config SH_PCLK_FREQ
         int "Peripheral clock frequency (in Hz)"
         default "27000000" if CPU_SUBTYPE_SH73180 || CPU_SUBTYPE_SH7343
diff --git a/arch/sh/kernel/time.c b/arch/sh/kernel/time.c
index c55d6f217a46..1b91c7214979 100644
--- a/arch/sh/kernel/time.c
+++ b/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
diff --git a/include/asm-sh/timer.h b/include/asm-sh/timer.h
index 5a014bca9d58..17b5e76a4c31 100644
--- a/include/asm-sh/timer.h
+++ b/include/asm-sh/timer.h
@@ -18,8 +18,29 @@ struct sys_timer {
 
         struct sys_device       dev;
         struct sys_timer_ops    *ops;
+
+#ifdef CONFIG_NO_IDLE_HZ
+        struct dyn_tick_timer   *dyn_tick;
+#endif
 };
 
+#ifdef CONFIG_NO_IDLE_HZ
+#define DYN_TICK_ENABLED        (1 << 1)
+
+struct dyn_tick_timer {
+        spinlock_t      lock;
+        unsigned int    state;                  /* Current state */
+        int             (*enable)(void);        /* Enables dynamic tick */
+        int             (*disable)(void);       /* Disables dynamic tick */
+        void            (*reprogram)(unsigned long); /* Reprograms the timer */
+        int             (*handler)(int, void *);
+};
+
+void timer_dyn_reprogram(void);
+#else
+#define timer_dyn_reprogram()   do { } while (0)
+#endif
+
 #define TICK_SIZE (tick_nsec / 1000)
 
 extern struct sys_timer tmu_timer, cmt_timer, mtu2_timer;