linux-kernel - [PATCH] Allow CLOCK_TICK

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Date:	Tue, 17 Jul 2012 17:41:40 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	linux-kernel@...r.kernel.org
Cc:	John Stultz <john.stultz@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: [PATCH] Allow CLOCK_TICK_RATE to be undefined

This patch allows an architecture to not define CLOCK_TICK_RATE, in
which case ACTHZ defaults to (HZ << 8).

Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Acked-by: Arnd Bergmann <arnd@...db.de>
Cc: John Stultz <john.stultz@...aro.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
---
 include/linux/jiffies.h |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index 265e2c3..a2134be 100644
--- a/include/linux/jiffies.h
+++ b/include/linux/jiffies.h
@@ -39,9 +39,6 @@
 # error Invalid value of HZ.
 #endif
 
-/* LATCH is used in the interval timer and ftape setup. */
-#define LATCH  ((CLOCK_TICK_RATE + HZ/2) / HZ)	/* For divider */
-
 /* Suppose we want to divide two numbers NOM and DEN: NOM/DEN, then we can
  * improve accuracy by shifting LSH bits, hence calculating:
  *     (NOM << LSH) / DEN
@@ -54,8 +51,15 @@
 #define SH_DIV(NOM,DEN,LSH) (   (((NOM) / (DEN)) << (LSH))              \
                              + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN))
 
+#ifdef CLOCK_TICK_RATE
+/* LATCH is used in the interval timer and ftape setup. */
+#define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ)	/* For divider */
+
 /* HZ is the requested value. ACTHZ is actual HZ ("<< 8" is for accuracy) */
 #define ACTHZ (SH_DIV (CLOCK_TICK_RATE, LATCH, 8))
+#else
+#define ACTHZ (HZ << 8)
+#endif
 
 /* TICK_NSEC is the time between ticks in nsec assuming real ACTHZ */
 #define TICK_NSEC (SH_DIV (1000000UL * 1000, ACTHZ, 8))

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