[ARM] 4012/1: Clocksource for pxa

Add a clocksource driver for pxa2xx systems

Signed-off-by: Luotao Fu <[e-mail]>
Signed-off-by: Sascha Hauer <[e-mail]>
Signed-off-by: Nicolas Pitre <[e-mail]>
Signed-off-by: Russell King <[e-mail]>

arch/arm/mach-pxa/time.c

···
 #include <linux/signal.h>
 #include <linux/errno.h>
 #include <linux/sched.h>
+#include <linux/clocksource.h>
 
 #include <asm/system.h>
 #include <asm/hardware.h>
···
 	}
 	RCNR = current_time;
 	return 0;
-}
-
-/* IRQs are disabled before entering here from do_gettimeofday() */
-static unsigned long pxa_gettimeoffset (void)
-{
-	long ticks_to_match, elapsed, usec;
-
-	/* Get ticks before next timer match */
-	ticks_to_match = OSMR0 - OSCR;
-
-	/* We need elapsed ticks since last match */
-	elapsed = LATCH - ticks_to_match;
-
-	/* don't get fooled by the workaround in pxa_timer_interrupt() */
-	if (elapsed <= 0)
-		return 0;
-
-	/* Now convert them to usec */
-	usec = (unsigned long)(elapsed * (tick_nsec / 1000))/LATCH;
-
-	return usec;
 }
 
 #ifdef CONFIG_NO_IDLE_HZ
···
 	.handler	= pxa_timer_interrupt,
 };
 
+cycle_t pxa_get_cycles(void)
+{
+	return OSCR;
+}
+
+static struct clocksource clocksource_pxa = {
+	.name           = "pxa_timer",
+	.rating         = 200,
+	.read           = pxa_get_cycles,
+	.mask           = CLOCKSOURCE_MASK(32),
+	.shift          = 20,
+	.is_continuous  = 1,
+};
+
 static void __init pxa_timer_init(void)
 {
 	struct timespec tv;
···
 	OIER = OIER_E0;		/* enable match on timer 0 to cause interrupts */
 	OSMR0 = OSCR + LATCH;	/* set initial match */
 	local_irq_restore(flags);
+
+	/* on PXA OSCR runs continiously and is not written to, so we can use it
+	 * as clock source directly.
+	 */
+	clocksource_pxa.mult =
+		clocksource_hz2mult(CLOCK_TICK_RATE, clocksource_pxa.shift);
+	clocksource_register(&clocksource_pxa);
+
 }
 
 #ifdef CONFIG_NO_IDLE_HZ
···
 	.init		= pxa_timer_init,
 	.suspend	= pxa_timer_suspend,
 	.resume		= pxa_timer_resume,
-	.offset		= pxa_gettimeoffset,
 #ifdef CONFIG_NO_IDLE_HZ
 	.dyn_tick	= &pxa_dyn_tick,
 #endif