lib: time: Add microsecond timer

Add get_timer_us(), which is useful e.g. when we need higher
precision timestamps.
Signed-off-by: NMarek Vasut <marek.vasut+renesas@gmail.com>
Cc: Tom Rini <trini@konsulko.com>
Cc: Simon Glass <sjg@chromium.org>
[trini: Fixup arch/arm/mach-bcm283x/include/mach/timer.h]
Signed-off-by: NTom Rini <trini@konsulko.com>

arch/arm/mach-bcm283x/include/mach/timer.h

@@ -25,9 +25,6 @@ struct bcm2835_timer_regs {
 	u32 c2;
 	u32 c3;
 };
-
-extern ulong get_timer_us(ulong base);
-
 #endif
 
 #endif

include/time.h

@@ -13,6 +13,7 @@ unsigned long get_timer(unsigned long base);
  * Granularity may be larger than 1us if hardware does not support this.
  */
 unsigned long timer_get_us(void);
+uint64_t get_timer_us(uint64_t base);
 
 /*
  * timer_test_add_offset()

lib/time.c

@@ -134,6 +134,20 @@ ulong __weak get_timer(ulong base)
 	return tick_to_time(get_ticks()) - base;
 }
 
+static uint64_t notrace tick_to_time_us(uint64_t tick)
+{
+	ulong div = get_tbclk() / 1000;
+
+	tick *= CONFIG_SYS_HZ;
+	do_div(tick, div);
+	return tick;
+}
+
+uint64_t __weak get_timer_us(uint64_t base)
+{
+	return tick_to_time_us(get_ticks()) - base;
+}
+
 unsigned long __weak notrace timer_get_us(void)
 {
 	return tick_to_time(get_ticks() * 1000);