[PATCH] [ARM] Add ARCH_PROVIDES_UDELAY config option

[Colin Cross]

On SMP kernels, the loops_per_jiffy value is not scaled, leading to
udelays that are too long if the CPU frequency is scaled down from
the frequency at loops_per_jiffy calibration, 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 <ccross at android.com>
---
 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