[PATCH v3 3/3] timer: riscv_aclint_timer: add timer_get_boot_us for BOOTSTAGE

[Chanho Park]

timer_get_boot_us function is required to record the boot stages as
us-based timestamp.
To get a micro-second time from a timer tick, this converts the
formula like below to avoid zero result of (tick / rate) part.

From: time(us) = (tick / rate) * 10000000
To  : time(us) = (tick * 1000) / (rate / 1000)

Signed-off-by: Chanho Park <chanho61.park at samsung.com>
---
 drivers/timer/riscv_aclint_timer.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/timer/riscv_aclint_timer.c b/drivers/timer/riscv_aclint_timer.c
index e29d527c8d77..73fb87912851 100644
--- a/drivers/timer/riscv_aclint_timer.c
+++ b/drivers/timer/riscv_aclint_timer.c
@@ -6,6 +6,7 @@
 
 #include <common.h>
 #include <clk.h>
+#include <div64.h>
 #include <dm.h>
 #include <timer.h>
 #include <asm/io.h>
@@ -44,6 +45,28 @@ u64 notrace timer_early_get_count(void)
 }
 #endif
 
+#if CONFIG_IS_ENABLED(RISCV_MMODE) && CONFIG_IS_ENABLED(BOOTSTAGE)
+ulong timer_get_boot_us(void)
+{
+	int ret;
+	u64 ticks = 0;
+	u32 rate;
+
+	ret = dm_timer_init();
+	if (!ret) {
+		rate = timer_get_rate(gd->timer);
+		timer_get_count(gd->timer, &ticks);
+	} else {
+		rate = RISCV_MMODE_TIMER_FREQ;
+		ticks = readq((void __iomem *)MTIME_REG(RISCV_MMODE_TIMERBASE,
+							RISCV_MMODE_TIMEROFF));
+	}
+
+	/* Below is converted from time(us) = (tick / rate) * 10000000 */
+	return lldiv(ticks * 1000, (rate / 1000));
+}
+#endif
+
 static const struct timer_ops riscv_aclint_timer_ops = {
 	.get_count = riscv_aclint_timer_get_count,
 };
-- 
2.39.2