Convert alpha to use clocksources instead of arch_gettimeoffset

Alpha has a tsc like rpcc counter that it uses to manage time.
This can be converted to an actual clocksource instead of utilizing
the arch_gettimeoffset method that is really only there for legacy
systems with no continuous counter.

Further cleanups could be made if alpha converted to the clockevent
model.

CC: Thomas Gleixner <tglx@linutronix.de>
CC: Richard Henderson <rth@twiddle.net>
Acked-by: NIvan Kokshaysky <ink@jurassic.park.msu.ru>
Tested-by: NIvan Kokshaysky <ink@jurassic.park.msu.ru>
Signed-off-by: NMatt Turner <mattst88@gmail.com>
Signed-off-by: NJohn Stultz <johnstul@us.ibm.com>

arch/alpha/Kconfig

@@ -51,10 +51,6 @@ config GENERIC_TIME
 	bool
 	default y
 
-config ARCH_USES_GETTIMEOFFSET
-	bool
-	default y
-
 config GENERIC_CMOS_UPDATE
         def_bool y
 

arch/alpha/kernel/time.c

@@ -51,6 +51,7 @@
 #include <linux/mc146818rtc.h>
 #include <linux/time.h>
 #include <linux/timex.h>
+#include <linux/clocksource.h>
 
 #include "proto.h"
 #include "irq_impl.h"
@@ -332,6 +333,34 @@ rpcc_after_update_in_progress(void)
 	return rpcc();
 }
 
+#ifndef CONFIG_SMP
+/* Until and unless we figure out how to get cpu cycle counters
+   in sync and keep them there, we can't use the rpcc.  */
+static cycle_t read_rpcc(struct clocksource *cs)
+{
+	cycle_t ret = (cycle_t)rpcc();
+	return ret;
+}
+
+static struct clocksource clocksource_rpcc = {
+	.name                   = "rpcc",
+	.rating                 = 300,
+	.read                   = read_rpcc,
+	.mask                   = CLOCKSOURCE_MASK(32),
+	.flags                  = CLOCK_SOURCE_IS_CONTINUOUS
+};
+
+static inline void register_rpcc_clocksource(long cycle_freq)
+{
+	clocksource_calc_mult_shift(&clocksource_rpcc, cycle_freq, 4);
+	clocksource_register(&clocksource_rpcc);
+}
+#else /* !CONFIG_SMP */
+static inline void register_rpcc_clocksource(long cycle_freq)
+{
+}
+#endif /* !CONFIG_SMP */
+
 void __init
 time_init(void)
 {
@@ -385,6 +414,8 @@ time_init(void)
 		__you_loose();
 	}
 
+	register_rpcc_clocksource(cycle_freq);
+
 	state.last_time = cc1;
 	state.scaled_ticks_per_cycle
 		= ((unsigned long) HZ << FIX_SHIFT) / cycle_freq;
@@ -394,44 +425,6 @@ time_init(void)
 	alpha_mv.init_rtc();
 }
 
-/*
- * Use the cycle counter to estimate an displacement from the last time
- * tick.  Unfortunately the Alpha designers made only the low 32-bits of
- * the cycle counter active, so we overflow on 8.2 seconds on a 500MHz
- * part.  So we can't do the "find absolute time in terms of cycles" thing
- * that the other ports do.
- */
-u32 arch_gettimeoffset(void)
-{
-#ifdef CONFIG_SMP
-	/* Until and unless we figure out how to get cpu cycle counters
-	   in sync and keep them there, we can't use the rpcc tricks.  */
-	return 0;
-#else
-	unsigned long delta_cycles, delta_usec, partial_tick;
-
-	delta_cycles = rpcc() - state.last_time;
-	partial_tick = state.partial_tick;
-	/*
-	 * usec = cycles * ticks_per_cycle * 2**48 * 1e6 / (2**48 * ticks)
-	 *	= cycles * (s_t_p_c) * 1e6 / (2**48 * ticks)
-	 *	= cycles * (s_t_p_c) * 15625 / (2**42 * ticks)
-	 *
-	 * which, given a 600MHz cycle and a 1024Hz tick, has a
-	 * dynamic range of about 1.7e17, which is less than the
-	 * 1.8e19 in an unsigned long, so we are safe from overflow.
-	 *
-	 * Round, but with .5 up always, since .5 to even is harder
-	 * with no clear gain.
-	 */
-
-	delta_usec = (delta_cycles * state.scaled_ticks_per_cycle 
-		      + partial_tick) * 15625;
-	delta_usec = ((delta_usec / ((1UL << (FIX_SHIFT-6-1)) * HZ)) + 1) / 2;
-	return delta_usec * 1000;
-#endif
-}
-
 /*
  * In order to set the CMOS clock precisely, set_rtc_mmss has to be
  * called 500 ms after the second nowtime has started, because when