[ARM] Convert to constant-optimising udelay() implementation.

This allows us to eliminate a multiplication when we have a constant
delay value, as per x86.

diff --git a/arch/arm/kernel/armksyms.c b/arch/arm/kernel/armksyms.c
index ae9203853a77d4a8e8233d4d06c7ab7ad1e3eadb..1d0fcf411ec99f82f5f21aef8990dc65746c9148 100644 (file)
--- a/arch/arm/kernel/armksyms.c
+++ b/arch/arm/kernel/armksyms.c
@@ -60,7 +60,8 @@ EXPORT_SYMBOL_ALIAS(fp_send_sig,send_sig);
 EXPORT_SYMBOL(__backtrace);
 
        /* platform dependent support */
-EXPORT_SYMBOL(udelay);
+EXPORT_SYMBOL(__udelay);
+EXPORT_SYMBOL(__const_udelay);
 
        /* networking */
 EXPORT_SYMBOL(csum_partial);

diff --git a/arch/arm/lib/delay.S b/arch/arm/lib/delay.S
index 67cbd8697bb7678a344f8cbcbec8b61dd7224749..3c7f7e675dd8c777857ef10487b5c369c4e1d558 100644 (file)
--- a/arch/arm/lib/delay.S
+++ b/arch/arm/lib/delay.S
@@ -16,15 +16,16 @@ LC0:                .word   loops_per_jiffy
 /*
  * 0 <= r0 <= 2000
  */
-ENTRY(udelay)
+ENTRY(__udelay)
                mov     r2,     #0x6800
                orr     r2, r2, #0x00db
-               mul     r1, r0, r2
+               mul     r0, r2, r0
+ENTRY(__const_udelay)                          @ 0 <= r0 <= 0x01ffffff
                ldr     r2, LC0
-               ldr     r2, [r2]
-               mov     r1, r1, lsr #11
-               mov     r2, r2, lsr #11
-               mul     r0, r1, r2
+               ldr     r2, [r2]                @ max = 0x0fffffff
+               mov     r0, r0, lsr #11         @ max = 0x00003fff
+               mov     r2, r2, lsr #11         @ max = 0x0003ffff
+               mul     r0, r2, r0              @ max = 2^32-1
                movs    r0, r0, lsr #6
                RETINSTR(moveq,pc,lr)
 

diff --git a/include/asm-arm/delay.h b/include/asm-arm/delay.h
index 4ebcea03406de183bfe71a185dca511da4a8ee87..1704360e969964e9f59063ab862163fee4f52231 100644 (file)
--- a/include/asm-arm/delay.h
+++ b/include/asm-arm/delay.h
@@ -1,14 +1,22 @@
-#ifndef __ASM_ARM_DELAY_H
-#define __ASM_ARM_DELAY_H
-
 /*
- * Copyright (C) 1995 Russell King
+ * Copyright (C) 1995-2004 Russell King
  *
  * Delay routines, using a pre-computed "loops_per_second" value.
  */
+#ifndef __ASM_ARM_DELAY_H
+#define __ASM_ARM_DELAY_H
 
 extern void __delay(int loops);
 
+/*
+ * This function intentionally does not exist; if you see references to
+ * it, it means that you're calling udelay() with an out of range value.
+ *
+ * With currently imposed limits, this means that we support a max delay
+ * of 2000us and 671 bogomips
+ */
+extern void __bad_udelay(void);
+
 /*
  * division by multiplication: you don't have to worry about
  * loss of precision.
@@ -19,14 +27,16 @@ extern void __delay(int loops);
  * first constant multiplications gets optimized away if the delay is
  * a constant)
  */
-extern void udelay(unsigned long usecs);
+extern void __udelay(unsigned long usecs);
+extern void __const_udelay(unsigned long);
 
-static inline unsigned long muldiv(unsigned long a, unsigned long b, unsigned long c)
-{
-       return a * b / c;
-}
+#define MAX_UDELAY_MS 2
 
-       
+#define udelay(n)                                              \
+       (__builtin_constant_p(n) ?                              \
+         ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() :      \
+                       __const_udelay((n) * 0x68dbul)) :       \
+         __udelay(n))
 
 #endif /* defined(_ARM_DELAY_H) */