[U-Boot] [PATCH v2 4/5] time: import time_after, time_before and friends from Linux
Masahiro Yamada
yamada.masahiro at socionext.com
Tue Dec 27 16:36:02 CET 2016
It is not safe to compare timer values directly.
On 32-bit systems, for example, timer_get_us() wraps around every
72 min. (2 ^ 32 / 1000000 =~ 4295 sec =~ 72 min). Depending on
the get_ticks() implementation, it may wrap more frequently.
The 72 min might be possible on the use of U-Boot.
Let's borrow time_after, time_before, and friends to solve the
wrap-around problem.
These macros were copied from include/linux/jiffies.h of Linux 4.9.
Signed-off-by: Masahiro Yamada <yamada.masahiro at socionext.com>
---
Changes in v2: None
include/time.h | 41 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)
diff --git a/include/time.h b/include/time.h
index 5ed021f..5746ad9 100644
--- a/include/time.h
+++ b/include/time.h
@@ -5,6 +5,8 @@
#ifndef _TIME_H
#define _TIME_H
+#include <linux/typecheck.h>
+
unsigned long get_timer(unsigned long base);
/*
@@ -13,4 +15,43 @@ unsigned long get_timer(unsigned long base);
*/
unsigned long timer_get_us(void);
+/*
+ * These inlines deal with timer wrapping correctly. You are
+ * strongly encouraged to use them
+ * 1. Because people otherwise forget
+ * 2. Because if the timer wrap changes in future you won't have to
+ * alter your driver code.
+ *
+ * time_after(a,b) returns true if the time a is after time b.
+ *
+ * Do this with "<0" and ">=0" to only test the sign of the result. A
+ * good compiler would generate better code (and a really good compiler
+ * wouldn't care). Gcc is currently neither.
+ */
+#define time_after(a,b) \
+ (typecheck(unsigned long, a) && \
+ typecheck(unsigned long, b) && \
+ ((long)((b) - (a)) < 0))
+#define time_before(a,b) time_after(b,a)
+
+#define time_after_eq(a,b) \
+ (typecheck(unsigned long, a) && \
+ typecheck(unsigned long, b) && \
+ ((long)((a) - (b)) >= 0))
+#define time_before_eq(a,b) time_after_eq(b,a)
+
+/*
+ * Calculate whether a is in the range of [b, c].
+ */
+#define time_in_range(a,b,c) \
+ (time_after_eq(a,b) && \
+ time_before_eq(a,c))
+
+/*
+ * Calculate whether a is in the range of [b, c).
+ */
+#define time_in_range_open(a,b,c) \
+ (time_after_eq(a,b) && \
+ time_before(a,c))
+
#endif /* _TIME_H */
--
2.7.4
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