[ARM] 2862/1: VST aka CONFIG_NO_IDLE_HZ support for PXA2xx

Patch from Nicolas Pitre

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/Kconfig

@@ -365,8 +365,8 @@ config NO_IDLE_HZ
 
 	  Please note that dynamic tick may affect the accuracy of
 	  timekeeping on some platforms depending on the implementation.
-	  Currently at least OMAP platform is known to have accurate
-	  timekeeping with dynamic tick.
+	  Currently at least OMAP and PXA2xx platforms are known to have
+	  accurate timekeeping with dynamic tick.
 
 config ARCH_DISCONTIGMEM_ENABLE
 	bool

arch/arm/mach-pxa/time.c

@@ -70,6 +70,11 @@ static unsigned long pxa_gettimeoffset (void)
 	return usec;
 }
 
+#ifdef CONFIG_NO_IDLE_HZ
+static unsigned long initial_match;
+static int match_posponed;
+#endif
+
 static irqreturn_t
 pxa_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
 {
@@ -77,6 +82,13 @@ pxa_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
 
 	write_seqlock(&xtime_lock);
 
+#ifdef CONFIG_NO_IDLE_HZ
+	if (match_posponed) {
+		match_posponed = 0;
+		OSMR0 = initial_match;
+	}
+#endif
+
 	/* Loop until we get ahead of the free running timer.
 	 * This ensures an exact clock tick count and time accuracy.
 	 * IRQs are disabled inside the loop to ensure coherence between
@@ -126,6 +138,42 @@ static void __init pxa_timer_init(void)
 	OSCR = 0;		/* initialize free-running timer, force first match */
 }
 
+#ifdef CONFIG_NO_IDLE_HZ
+static int pxa_dyn_tick_enable_disable(void)
+{
+	/* nothing to do */
+	return 0;
+}
+
+static void pxa_dyn_tick_reprogram(unsigned long ticks)
+{
+	if (ticks > 1) {
+		initial_match = OSMR0;
+		OSMR0 = initial_match + ticks * LATCH;
+		match_posponed = 1;
+	}
+}
+
+static irqreturn_t
+pxa_dyn_tick_handler(int irq, void *dev_id, struct pt_regs *regs)
+{
+	if (match_posponed) {
+		match_posponed = 0;
+		OSMR0 = initial_match;
+		if ( (signed long)(initial_match - OSCR) <= 8 )
+			return pxa_timer_interrupt(irq, dev_id, regs);
+	}
+	return IRQ_NONE;
+}
+
+static struct dyn_tick_timer pxa_dyn_tick = {
+	.enable		= pxa_dyn_tick_enable_disable,
+	.disable	= pxa_dyn_tick_enable_disable,
+	.reprogram	= pxa_dyn_tick_reprogram,
+	.handler	= pxa_dyn_tick_handler,
+};
+#endif
+
 #ifdef CONFIG_PM
 static unsigned long osmr[4], oier;
 
@@ -161,4 +209,7 @@ struct sys_timer pxa_timer = {
 	.suspend	= pxa_timer_suspend,
 	.resume		= pxa_timer_resume,
 	.offset		= pxa_gettimeoffset,
+#ifdef CONFIG_NO_IDLE_HZ
+	.dyn_tick	= &pxa_dyn_tick,
+#endif
 };