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arm: Translate delay.S into (mostly) C

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In the next patch we're going to allow machines to override the
__delay() implementation at runtime so they can implement a timer
based __delay() routine. It's easier to do this using C, so lets
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 the next patch
adds functionality to allow a machine to set the __delay() loop
themselves, therefore allowing machines to resurrect the
commented out code if they need it.

bloat-o-meter shows an increase of 12 bytes. Further inspection
of the assembly shows GCC copying the loops_per_jiffy pointer and
the magic HZ value to the ends of __const_udelay() and _delay()
thus contributing an extra 4 and 8 bytes of data to each
function. These two values weren't taken into account in the
delay.S version since they weren't part of the function in nm's
eyes. This means we only really gained an extra 4 bytes due to
GCC's decision to duplicate the loops_per_jiffy pointer in
__const_udelay.

 $ scripts/bloat-o-meter vmlinux.orig vmlinux.new
 add/remove: 0/0 grow/shrink: 2/0 up/down: 12/0 (12)
 function                                     old     new   delta
 __udelay                                      48      56      +8
 __const_udelay                                40      44      +4

Change-Id: Ibfaab52d0f5e09471571be082232db04726d5532
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Reviewed-by: Saravana Kannan <skannan@codeaurora.org>
(cherry picked from commit 8d5868d8205d10a0a8e423f53e9cc9bb3e9d1a34)

Conflicts:

	arch/arm/kernel/armksyms.c
	arch/arm/lib/delay.S
This commit is contained in:
Stephen Boyd
2010-08-12 13:33:12 -07:00
parent 5d8bc2351b
commit e89a2fd996
4 changed files with 58 additions and 74 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
arch/arm/include/asm/delay.h
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@@ -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

4
arch/arm/kernel/armksyms.c
View File

@@ -48,10 +48,6 @@ extern void __aeabi_ulcmp(void);
extern void fpundefinstr(void);
/* platform dependent support */
EXPORT_SYMBOL(__udelay);
EXPORT_SYMBOL(__const_udelay);
/* networking */
EXPORT_SYMBOL(csum_partial);
EXPORT_SYMBOL(csum_partial_copy_from_user);

69
arch/arm/lib/delay.S
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@@ -1,69 +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
mov r1, #-1
ldr r2, .LC0
ldr r2, [r2] @ max = 0x01ffffff
add r0, r0, r1, lsr #32-14
mov r0, r0, lsr #14 @ max = 0x0001ffff
add r2, r2, r1, lsr #32-10
mov r2, r2, lsr #10 @ max = 0x00007fff
mul r0, r2, r0 @ max = 2^32-1
add r0, r0, r1, lsr #32-6
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)

57
arch/arm/lib/delay.c Normal file
View File

@@ -0,0 +1,57 @@
/*
* Originally from linux/arch/arm/lib/delay.S
*
* Copyright (C) 1995, 1996 Russell King
* Copyright (c) 2010, Code Aurora Forum. All rights reserved.
*
* 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 (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);