[v2,4/5] time: import time_after, time_before and friends from Linux

Message ID 1482852963-6887-5-git-send-email-yamada.masahiro@socionext.com
State New
Headers show

Commit Message

Masahiro Yamada Dec. 27, 2016, 3:36 p.m.
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(+)

-- 
2.7.4

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Comments

Simon Glass Jan. 12, 2017, 5:07 a.m. | #1
On 27 December 2016 at 08:36, Masahiro Yamada
<yamada.masahiro@socionext.com> 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 / 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(+)


Reviewed-by: Simon Glass <sjg@chromium.org>

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Tom Rini Jan. 15, 2017, 6:29 p.m. | #2
On Wed, Dec 28, 2016 at 12:36:02AM +0900, 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 / 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>

> Reviewed-by: Simon Glass <sjg@chromium.org>


Applied to u-boot/master, thanks!

-- 
Tom
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Patch

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 */