Subject: [PATCH V2] [ARM] Add ARCH_PROVIDES_UDELAY config option

From: [email-masked] (Colin Cross)
Date: Fri, 30 Apr 2010 12:12:16 -0700

On SMP kernels, the loops_per_jiffy value is not scaled due to the
possibility of one CPU affecting the speed of another CPU while the
second CPU is in a udelay loop.  Since loops_per_jiffy is calculated
once on boot for SMP kernels, udelays are too long if the CPU
frequency is scaled down from the boot frequency, or too short if the
frequency is scaled up.  Some SOCs have a timer with a constant tick
rate that can be used to time udelays, similar to the TSC on x86.
Provide a config flag to allow these SOCs to override the default
ARM udelay implementation.

Signed-off-by: Colin Cross <[email-masked]>
---
 arch/arm/Kconfig             |    3 +++
 arch/arm/include/asm/delay.h |    4 ++++
 arch/arm/lib/Makefile        |    6 +++++-
 3 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 33d2825..d9923b0 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -175,6 +175,9 @@ config ARM_L1_CACHE_SHIFT_6
 	help
 	  Setting ARM L1 cache line size to 64 Bytes.
 
+config ARCH_PROVIDES_UDELAY
+  bool
+
 if OPROFILE
 
 config OPROFILE_ARMV6
diff --git a/arch/arm/include/asm/delay.h b/arch/arm/include/asm/delay.h
index b2deda1..57f1fa0 100644
--- a/arch/arm/include/asm/delay.h
+++ b/arch/arm/include/asm/delay.h
@@ -8,6 +8,9 @@
 
 #include <asm/param.h>	/* HZ */
 
+#ifdef CONFIG_ARCH_PROVIDES_UDELAY
+#include <mach/delay.h>
+#else
 extern void __delay(int loops);
 
 /*
@@ -40,5 +43,6 @@ extern void __const_udelay(unsigned long);
 			__const_udelay((n) * ((2199023U*HZ)>>11))) :	\
 	  __udelay(n))
 
+#endif /* defined(ARCH_PROVIDES_UDELAY) */
 #endif /* defined(_ARM_DELAY_H) */
 
diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index 030ba72..aa449e3 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -6,7 +6,7 @@
 
 lib-y		:= backtrace.o changebit.o csumipv6.o csumpartial.o   \
 		   csumpartialcopy.o csumpartialcopyuser.o clearbit.o \
-		   delay.o findbit.o memchr.o memcpy.o		      \
+		   findbit.o memchr.o memcpy.o                        \
 		   memmove.o memset.o memzero.o setbit.o              \
 		   strncpy_from_user.o strnlen_user.o                 \
 		   strchr.o strrchr.o                                 \
@@ -17,6 +17,10 @@ lib-y		:= backtrace.o changebit.o csumipv6.o csumpartial.o   \
 
 mmu-y	:= clear_user.o copy_page.o getuser.o putuser.o
 
+ifneq ($(CONFIG_ARCH_PROVIDES_UDELAY),y)
+  lib-y += delay.o
+endif
+
 # the code in uaccess.S is not preemption safe and
 # probably faster on ARMv3 only
 ifeq ($(CONFIG_PREEMPT),y)
-- 
1.5.4.3