1 files changed, 79 insertions, 0 deletions
diff --git a/arch/x86/include/asm/timer.h b/arch/x86/include/asm/timer.h
new file mode 100644
index 00000000..34baa0eb
--- /dev/null
+++ b/arch/x86/include/asm/timer.h
@@ -0,0 +1,79 @@
+#ifndef _ASM_X86_TIMER_H
+#define _ASM_X86_TIMER_H
+#include <linux/init.h>
+#include <linux/pm.h>
+#include <linux/percpu.h>
+#include <linux/interrupt.h>
+
+#define TICK_SIZE (tick_nsec / 1000)
+
+unsigned long long native_sched_clock(void);
+extern int recalibrate_cpu_khz(void);
+
+extern int no_timer_check;
+
+/* Accelerators for sched_clock()
+ * convert from cycles(64bits) => nanoseconds (64bits)
+ *  basic equation:
+ *		ns = cycles / (freq / ns_per_sec)
+ *		ns = cycles * (ns_per_sec / freq)
+ *		ns = cycles * (10^9 / (cpu_khz * 10^3))
+ *		ns = cycles * (10^6 / cpu_khz)
+ *
+ *	Then we use scaling math (suggested by george@mvista.com) to get:
+ *		ns = cycles * (10^6 * SC / cpu_khz) / SC
+ *		ns = cycles * cyc2ns_scale / SC
+ *
+ *	And since SC is a constant power of two, we can convert the div
+ *  into a shift.
+ *
+ *  We can use khz divisor instead of mhz to keep a better precision, since
+ *  cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
+ *  (mathieu.desnoyers@polymtl.ca)
+ *
+ *			-johnstul@us.ibm.com "math is hard, lets go shopping!"
+ *
+ * In:
+ *
+ * ns = cycles * cyc2ns_scale / SC
+ *
+ * Although we may still have enough bits to store the value of ns,
+ * in some cases, we may not have enough bits to store cycles * cyc2ns_scale,
+ * leading to an incorrect result.
+ *
+ * To avoid this, we can decompose 'cycles' into quotient and remainder
+ * of division by SC.  Then,
+ *
+ * ns = (quot * SC + rem) * cyc2ns_scale / SC
+ *    = quot * cyc2ns_scale + (rem * cyc2ns_scale) / SC
+ *
+ *			- sqazi@google.com
+ */
+
+DECLARE_PER_CPU(unsigned long, cyc2ns);
+DECLARE_PER_CPU(unsigned long long, cyc2ns_offset);
+
+#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
+
+static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
+{
+	int cpu = smp_processor_id();
+	unsigned long long ns = per_cpu(cyc2ns_offset, cpu);
+	ns += mult_frac(cyc, per_cpu(cyc2ns, cpu),
+			(1UL << CYC2NS_SCALE_FACTOR));
+	return ns;
+}
+
+static inline unsigned long long cycles_2_ns(unsigned long long cyc)
+{
+	unsigned long long ns;
+	unsigned long flags;
+
+	local_irq_save(flags);
+	ns = __cycles_2_ns(cyc);
+	local_irq_restore(flags);
+
+	return ns;
+}
+
+#endif /* _ASM_X86_TIMER_H */