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@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 */