[PATCH] ARM: Generic Dynamic Tick Timer support for ARM, take 4

This patch adds support for Dynamic Tick Timer for ARM. Dynamic Tick is
also known as VST (Variable Scheduling Timeouts).

Dynamic Tick has been in use in the OMAP tree since last October.  The
patch is not intrusive, and does not do anything unless CONFIG_NO_IDLE_HZ
is defined.  This patch has the following fixed based on comments from
RMK:
- Time is updated before calling interrupt handlers.
- Added new interrupt flag SA_TIMER to avoid duplicate timer interrupts
- Moved struct dyn_tick_timer to time.h until we at some point probably
  have an arch independent dyn-tick.h
- Cleaned up testing for DYN_TICK_ENABLED in irq.c

 I've cleaned up this patch to fix some remaining issues:
 - Call the timer tick handler with irqs disabled, as it would be from
   a normal interrupt
 - if we have a dyn_tick, we better implement all methods.
 - generic timer_dyn_reprogram() call, to be called before sleeping
 - added command line option - "dyntick=" to allow boot-time control
   of this feature
    -- rmk

Signed-off-by: Tony Lindgren
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

include/asm-arm/mach/time.h

@@ -39,8 +39,29 @@ struct sys_timer {
 	void			(*suspend)(void);
 	void			(*resume)(void);
 	unsigned long		(*offset)(void);
+
+#ifdef CONFIG_NO_IDLE_HZ
+	struct dyn_tick_timer	*dyn_tick;
+#endif
 };
 
+#ifdef CONFIG_NO_IDLE_HZ
+
+#define DYN_TICK_SKIPPING	(1 << 2)
+#define DYN_TICK_ENABLED	(1 << 1)
+#define DYN_TICK_SUITABLE	(1 << 0)
+
+struct dyn_tick_timer {
+	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 *, struct pt_regs *);
+};
+
+void timer_dyn_reprogram(void);
+#endif
+
 extern struct sys_timer *system_timer;
 extern void timer_tick(struct pt_regs *);