[PATCH v6] introduce macro spin_event_timeout()

[Timur Tabi]

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 the result of the condition when the loop
was terminated.

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 at freescale.com>
---

I'm making this a PowerPC-specific patch because I want to use 
tb_ticks_per_usec, which does not exist on all other platforms.  I don't want
to use jiffies because jiffies works only when interrupts are enabled, and
the resolution may not be fine enough.

 arch/powerpc/include/asm/delay.h |   27 +++++++++++++++++++++++++++
 1 files changed, 27 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/include/asm/delay.h b/arch/powerpc/include/asm/delay.h
index f9200a6..1939e0f 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 +32,30 @@ 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
+ * @delay: the number of microseconds to delay between eache evaluation of
+ *         @condition
+ * @rc: the last value of the condition
+ *
+ * The process spins until the condition evaluates to true (non-zero) or the
+ * timeout elapses.  Upon exit, @rc contains the value of the condition. This
+ * allows you to test the condition without incurring any side effects.
+ *
+ * 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 delay is for devices that need a
+ * delay in between successive reads.
+ */
+#define spin_event_timeout(condition, timeout, delay, rc)                   \
+{                                                                           \
+	unsigned long __loops = tb_ticks_per_usec * timeout;                \
+	unsigned long __start = get_tbl();                                  \
+	while (!(rc = (condition)) && (tb_ticks_since(__start) <= __loops)) \
+		udelay(delay);                                      	    \
+}
+
 #endif /* __KERNEL__ */
 #endif /* _ASM_POWERPC_DELAY_H */
-- 
1.6.0.6