[U-Boot-Users] [Patch 02/17] U-Boot-V2:Common:Clock Handle case of clock rollover for get_time_ns

[Menon, Nishanth]

get_time_ns does a simplistic delta = cycle_now - cycle_last. It is possible that the h/w counter reached max and reset back to 0.
This patch addresses this issue by checking for rollover condition.

NOTE 1: This does not guarantee that you cannot confuse get_time_ns. You could possibly wait for two reset cycles and then get a messed up value.
To fix that we may need interrupt mode timer tick - something on the lines of jiffies on linux.
NOTE 2: the question of cs->mask is not clear. if the mask is for the tick, then it is better done with (cycle_now & cs->mask) - (cs->cycle_last & cs->mask). Do we need min and max for register read?

Signed-off-by: Nishanth Menon<x0nishan at ti.com>

---
 common/clock.c |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

Index: u-boot-v2.git/common/clock.c
===================================================================
--- u-boot-v2.git.orig/common/clock.c	2008-05-20 17:19:44.000000000 -0500
+++ u-boot-v2.git/common/clock.c	2008-05-20 17:26:31.000000000 -0500
@@ -37,14 +37,24 @@
 uint64_t get_time_ns(void)
 {
 	struct clocksource *cs = current_clock;
-        uint64_t cycle_now, cycle_delta;
+	uint64_t cycle_now, cycle_delta = 0;
         uint64_t ns_offset;
 
         /* read clocksource: */
         cycle_now = cs->read();
 
         /* calculate the delta since the last call: */
-        cycle_delta = (cycle_now - cs->cycle_last) & cs->mask;
+
+	/* Handle rollover case */
+	if (cycle_now < cs->cycle_last) {
+		/* FIXME: I am not convinced about the cs->mask operation..
+		 * I am assuming cs->mask is max! Probably need to change
+		 * clocksource structure to have min and max
+		 */
+		cycle_delta = cs->mask - (cs->cycle_last & cs->mask);
+		cs->cycle_last = 0;
+	}
+	cycle_delta += (cycle_now & cs->mask) - (cs->cycle_last & cs->mask);
 
         /* convert to nanoseconds: */
         ns_offset = cyc2ns(cs, cycle_delta);