x86: Add function to read time stamp counter

Put this function in the u-boot-x86.h header file. We could instead create
timer.h perhaps.

We support setting a base time, and reading the time relative to this base.

Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Signed-off-by: Stefan Reinauer <reinauer@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>

arch/x86/include/asm/u-boot-x86.h

@@ -68,4 +68,16 @@ int video_init(void);
 void	board_init_f_r_trampoline(ulong) __attribute__ ((noreturn));
 void	board_init_f_r(void) __attribute__ ((noreturn));
 
+/* Read the time stamp counter */
+static inline uint64_t rdtsc(void)
+{
+	uint32_t high, low;
+	__asm__ __volatile__("rdtsc" : "=a" (low), "=d" (high));
+	return (((uint64_t)high) << 32) | low;
+}
+
+/* board/... */
+void timer_set_tsc_base(uint64_t new_base);
+uint64_t timer_get_tsc(void);
+
 #endif	/* _U_BOOT_I386_H_ */

arch/x86/lib/timer.c

@@ -37,6 +37,7 @@ struct timer_isr_function {
 
 static struct timer_isr_function *first_timer_isr;
 static unsigned long system_ticks;
+static uint64_t base_value;
 
 /*
  * register_timer_isr() allows multiple architecture and board specific
@@ -98,3 +99,19 @@ ulong get_timer(ulong base)
 {
 	return system_ticks - base;
 }
+
+void timer_set_tsc_base(uint64_t new_base)
+{
+	base_value = new_base;
+}
+
+uint64_t timer_get_tsc(void)
+{
+	uint64_t time_now;
+
+	time_now = rdtsc();
+	if (!base_value)
+		base_value = time_now;
+
+	return time_now - base_value;
+}