Re: [U-Boot] [PATCH v2 4/5] time: import time_after, time_before and friends from Linux

[Simon Glass]

On 27 December 2016 at 08:36, Masahiro Yamada
 wrote:
> 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 / 100 =~ 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 
> ---
>
> Changes in v2: None
>
>  include/time.h | 41 +
>  1 file changed, 41 insertions(+)

Reviewed-by: Simon Glass 
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[U-Boot] [PATCH v2 4/5] time: import time_after, time_before and friends from Linux

[Masahiro Yamada]

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 / 100 =~ 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 
---

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 
+
 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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