[PATCH v5] introduce macro spin_event_timeout()

[Timur Tabi <timur@freescale.com>]

The macro spin_event_timeout() takes a condition and timeout value
(in microseconds) as parameters.  It spins until either the condition is true
or the timeout expires.  It returns zero if the timeout expires first, non-zero
otherwise.

This primary purpose of this macro is to poll on a hardware register until a
status bit changes.  The timeout ensures that the loop still terminates if the
bit doesn't change as expected.  This macro makes it easier for driver
developers to perform this kind of operation properly.

Signed-off-by: Timur Tabi <timur@freescale.com>
---

v5: ported to arch/powerpc, made it powerpc-specific, eliminated udelay

v4: removed cpu_relax (redundant), changed timeout to unsigned long

v3: eliminated secondary evaluation of condition, replaced jiffies with udelay

v2: added cpu_relax and time_before

 arch/powerpc/include/asm/delay.h |   32 ++++++++++++++++++++++++++++++++
 1 files changed, 32 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/include/asm/delay.h b/arch/powerpc/include/asm/delay.h
index f9200a6..aadec70 100644
--- a/arch/powerpc/include/asm/delay.h
+++ b/arch/powerpc/include/asm/delay.h
@@ -2,6 +2,8 @@
 #define _ASM_POWERPC_DELAY_H
 #ifdef __KERNEL__
 
+#include <asm/time.h>
+
 /*
  * Copyright 1996, Paul Mackerras.
  *
@@ -30,5 +32,35 @@ extern void udelay(unsigned long usecs);
 #define mdelay(n)	udelay((n) * 1000)
 #endif
 
+/**
+ * spin_event_timeout - spin until a condition gets true or a timeout elapses
+ * @condition: a C expression to evalate
+ * @timeout: timeout, in microseconds
+ *
+ * The process spins until the @condition evaluates to true (non-zero) or
+ * the @timeout elapses.
+ *
+ * This primary purpose of this macro is to poll on a hardware register
+ * until a status bit changes.  The timeout ensures that the loop still
+ * terminates if the bit never changes.
+ *
+ * The return value is non-zero if the condition evaluates to true first, or
+ * zero if the timeout elapses first.
+ */
+#define spin_event_timeout(condition, timeout)			\
+({								\
+	unsigned long __start = get_tbl();			\
+	unsigned long __loops = tb_ticks_per_usec * timeout;	\
+	int __ret = 1;						\
+	while (!(condition)) {					\
+		if (tb_ticks_since(__start) > __loops) {	\
+			__ret = 0;				\
+			break;					\
+		}						\
+		cpu_relax();					\
+	}							\
+	__ret;							\
+})
+
 #endif /* __KERNEL__ */
 #endif /* _ASM_POWERPC_DELAY_H */
-- 
1.6.1.3