The patch titled
arm: translate delay.S into (mostly) C
has been added to the -mm tree. Its filename is
arm-translate-delays-into-mostly-c.patch
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------------------------------------------------------
Subject: arm: translate delay.S into (mostly) C
From: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
We want to allow machines to override the __delay() implementation at
runtime so they can use a timer based __delay() routine. It's easier to
do this using C, so let's write udelay and friends in C.
We lose the #if 0 code, which according to Russell is used "to make the
delay loop more stable and predictable on older CPUs" (see
http://article.gmane.org/gmane.linux.kernel/888867 for more info). We
shouldn't be too worried though, since we'll soon add functionality
allowing a machine to set the __delay() loop themselves, thus allowing
machines to resurrect the commented out code should they need it.
Nico expressed concern that fixed lpj cmdlines will break due to compiler
optimizations. That doesn't seem to be the case since before and after
this patch I get the same lpj value when running my CPU at 19.2 MHz. That
should be sufficiently slow enough to cover any machine running Linux.
This will break builds when you switch back and forth without this patch.
You need to rm arch/arm/lib/.delay.o.cmd if you ever build a kernel before
this patch after you've built with this patch.
delete mode 100644 arch/arm/lib/delay.S
create mode 100644 arch/arm/lib/delay.c
Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
Reviewed-by: Saravana Kannan <skannan@xxxxxxxxxxxxxx>
Acked-by: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/arm/include/asm/delay.h | 2 -
arch/arm/kernel/armksyms.c | 4 --
arch/arm/lib/delay.S | 65 ---------------------------------
arch/arm/lib/delay.c | 56 ++++++++++++++++++++++++++++
4 files changed, 57 insertions(+), 70 deletions(-)
diff -puN arch/arm/include/asm/delay.h~arm-translate-delays-into-mostly-c arch/arm/include/asm/delay.h
--- a/arch/arm/include/asm/delay.h~arm-translate-delays-into-mostly-c
+++ a/arch/arm/include/asm/delay.h
@@ -8,7 +8,7 @@
#include <asm/param.h> /* HZ */
-extern void __delay(int loops);
+extern void __delay(unsigned long loops);
/*
* This function intentionally does not exist; if you see references to
diff -puN arch/arm/kernel/armksyms.c~arm-translate-delays-into-mostly-c arch/arm/kernel/armksyms.c
--- a/arch/arm/kernel/armksyms.c~arm-translate-delays-into-mostly-c
+++ a/arch/arm/kernel/armksyms.c
@@ -52,10 +52,6 @@ extern void fpundefinstr(void);
EXPORT_SYMBOL(__backtrace);
- /* platform dependent support */
-EXPORT_SYMBOL(__udelay);
-EXPORT_SYMBOL(__const_udelay);
-
/* networking */
EXPORT_SYMBOL(csum_partial);
EXPORT_SYMBOL(csum_partial_copy_from_user);
diff -puN arch/arm/lib/delay.S~arm-translate-delays-into-mostly-c /dev/null
--- a/arch/arm/lib/delay.S
+++ /dev/null
@@ -1,65 +0,0 @@
-/*
- * linux/arch/arm/lib/delay.S
- *
- * Copyright (C) 1995, 1996 Russell King
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- */
-#include <linux/linkage.h>
-#include <asm/assembler.h>
-#include <asm/param.h>
- .text
-
-.LC0: .word loops_per_jiffy
-.LC1: .word (2199023*HZ)>>11
-
-/*
- * r0 <= 2000
- * lpj <= 0x01ffffff (max. 3355 bogomips)
- * HZ <= 1000
- */
-
-ENTRY(__udelay)
- ldr r2, .LC1
- mul r0, r2, r0
-ENTRY(__const_udelay) @ 0 <= r0 <= 0x7fffff06
- ldr r2, .LC0
- ldr r2, [r2] @ max = 0x01ffffff
- mov r0, r0, lsr #14 @ max = 0x0001ffff
- mov r2, r2, lsr #10 @ max = 0x00007fff
- mul r0, r2, r0 @ max = 2^32-1
- movs r0, r0, lsr #6
- moveq pc, lr
-
-/*
- * loops = r0 * HZ * loops_per_jiffy / 1000000
- *
- * Oh, if only we had a cycle counter...
- */
-
-@ Delay routine
-ENTRY(__delay)
- subs r0, r0, #1
-#if 0
- movls pc, lr
- subs r0, r0, #1
- movls pc, lr
- subs r0, r0, #1
- movls pc, lr
- subs r0, r0, #1
- movls pc, lr
- subs r0, r0, #1
- movls pc, lr
- subs r0, r0, #1
- movls pc, lr
- subs r0, r0, #1
- movls pc, lr
- subs r0, r0, #1
-#endif
- bhi __delay
- mov pc, lr
-ENDPROC(__udelay)
-ENDPROC(__const_udelay)
-ENDPROC(__delay)
diff -puN /dev/null arch/arm/lib/delay.c
--- /dev/null
+++ a/arch/arm/lib/delay.c
@@ -0,0 +1,56 @@
+/*
+ * Originally from linux/arch/arm/lib/delay.S
+ *
+ * Copyright (C) 1995, 1996 Russell King
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <linux/module.h>
+#include <linux/delay.h>
+
+/*
+ * loops = usecs * HZ * loops_per_jiffy / 1000000
+ *
+ * Oh, if only we had a cycle counter...
+ */
+void __delay(unsigned long loops)
+{
+ asm volatile(
+ "1: subs %0, %0, #1 \n"
+ " bhi 1b \n"
+ : /* No output */
+ : "r" (loops)
+ );
+}
+EXPORT_SYMBOL(__delay);
+
+/*
+ * 0 <= xloops <= 0x7fffff06
+ * loops_per_jiffy <= 0x01ffffff (max. 3355 bogomips)
+ */
+void __const_udelay(unsigned long xloops)
+{
+ unsigned long lpj;
+ unsigned long loops;
+
+ xloops >>= 14; /* max = 0x01ffffff */
+ lpj = loops_per_jiffy >> 10; /* max = 0x0001ffff */
+ loops = lpj * xloops; /* max = 0x00007fff */
+ loops >>= 6; /* max = 2^32-1 */
+
+ if (likely(loops))
+ __delay(loops);
+}
+EXPORT_SYMBOL(__const_udelay);
+
+/*
+ * usecs <= 2000
+ * HZ <= 1000
+ */
+void __udelay(unsigned long usecs)
+{
+ __const_udelay(usecs * ((2199023*HZ)>>11));
+}
+EXPORT_SYMBOL(__udelay);
_
Patches currently in -mm which might be from sboyd@xxxxxxxxxxxxxx are
arm-translate-delays-into-mostly-c.patch
arm-allow-machines-to-override-__delay.patch
arm-implement-a-timer-based-__delay-loop.patch
msm-timer-migrate-to-timer-based-__delay.patch
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