---

yaml
---
r: 223450
b: refs/heads/master
c: b8da46d
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: de5e9d58200aafea4a33abcadcd12eb69eaba5c4
+refs/heads/master: b8da46d3d55807037b58f14621a0949f18053bde

trunk/arch/mn10300/kernel/time.c

@@ -40,21 +40,17 @@ unsigned long long sched_clock(void)
 		unsigned long long ll;
 		unsigned l[2];
 	} tsc64, result;
-	unsigned long tsc, tmp;
+	unsigned long tmp;
 	unsigned product[3]; /* 96-bit intermediate value */
 
 	/* cnt32_to_63() is not safe with preemption */
 	preempt_disable();
 
-	/* read the TSC value
-	 */
-	tsc = get_cycles();
-
-	/* expand to 64-bits.
+	/* expand the tsc to 64-bits.
 	 * - sched_clock() must be called once a minute or better or the
 	 *   following will go horribly wrong - see cnt32_to_63()
 	 */
-	tsc64.ll = cnt32_to_63(tsc) & 0x7fffffffffffffffULL;
+	tsc64.ll = cnt32_to_63(get_cycles()) & 0x7fffffffffffffffULL;
 
 	preempt_enable();
 

trunk/include/linux/cnt32_to_63.h

@@ -61,13 +61,31 @@ union cnt32_to_63 {
  *
  * 2) this code must not be preempted for a duration longer than the
  *    32-bit counter half period minus the longest period between two
- *    calls to this code.
+ *    calls to this code;
  *
  * Those requirements ensure proper update to the state bit in memory.
  * This is usually not a problem in practice, but if it is then a kernel
  * timer should be scheduled to manage for this code to be executed often
  * enough.
  *
+ * And finally:
+ *
+ * 3) the cnt_lo argument must be seen as a globally incrementing value,
+ *    meaning that it should be a direct reference to the counter data which
+ *    can be evaluated according to a specific ordering within the macro,
+ *    and not the result of a previous evaluation stored in a variable.
+ *
+ * For example, this is wrong:
+ *
+ *	u32 partial = get_hw_count();
+ *	u64 full = cnt32_to_63(partial);
+ *	return full;
+ *
+ * This is fine:
+ *
+ *	u64 full = cnt32_to_63(get_hw_count());
+ *	return full;
+ *
  * Note that the top bit (bit 63) in the returned value should be considered
  * as garbage.  It is not cleared here because callers are likely to use a
  * multiplier on the returned value which can get rid of the top bit