[ARM] 4550/1: sched_clock on PXA should cope with run time clock rate selection

The previous implementation was relying on compile time optimizations
based on a constant clock rate.  However, support for different PXA
flavors in the same kernel binary requires that the clock be selected at
run time, so here it is.

Let's move this code to a more appropriate location while at it.

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

1 files changed, 39 insertions, 0 deletions

diff --git a/arch/arm/mach-pxa/time.c b/arch/arm/mach-pxa/time.c
index 98d27e646b09..7916311547ca 100644
--- a/arch/arm/mach-pxa/time.c
+++ b/arch/arm/mach-pxa/time.c
@@ -16,11 +16,48 @@
 #include <linux/init.h>
 #include <linux/interrupt.h>
 #include <linux/clockchips.h>
+#include <linux/sched.h>
 
+#include <asm/div64.h>
+#include <asm/cnt32_to_63.h>
 #include <asm/mach/irq.h>
 #include <asm/mach/time.h>
 #include <asm/arch/pxa-regs.h>
 
+/*
+ * This is PXA's sched_clock implementation. This has a resolution
+ * of at least 308 ns and a maximum value of 208 days.
+ *
+ * The return value is guaranteed to be monotonic in that range as
+ * long as there is always less than 582 seconds between successive
+ * calls to sched_clock() which should always be the case in practice.
+ */
+
+#define OSCR2NS_SCALE_FACTOR 10
+
+static unsigned long oscr2ns_scale;
+
+static void __init set_oscr2ns_scale(unsigned long oscr_rate)
+{
+	unsigned long long v = 1000000000ULL << OSCR2NS_SCALE_FACTOR;
+	do_div(v, oscr_rate);
+	oscr2ns_scale = v;
+	/*
+	 * We want an even value to automatically clear the top bit
+	 * returned by cnt32_to_63() without an additional run time
+	 * instruction. So if the LSB is 1 then round it up.
+	 */
+	if (oscr2ns_scale & 1)
+		oscr2ns_scale++;
+}
+
+unsigned long long sched_clock(void)
+{
+	unsigned long long v = cnt32_to_63(OSCR);
+	return (v * oscr2ns_scale) >> OSCR2NS_SCALE_FACTOR;
+}
+
+
 static irqreturn_t
 pxa_ost0_interrupt(int irq, void *dev_id)
 {
@@ -152,6 +189,8 @@ static void __init pxa_timer_init(void)
 	OIER = 0;
 	OSSR = OSSR_M0 | OSSR_M1 | OSSR_M2 | OSSR_M3;
 
+	set_oscr2ns_scale(CLOCK_TICK_RATE);
+
 	ckevt_pxa_osmr0.mult =
 		div_sc(CLOCK_TICK_RATE, NSEC_PER_SEC, ckevt_pxa_osmr0.shift);
 	ckevt_pxa_osmr0.max_delta_ns =