[ARM] 3346/1: Fix udelay() for HZ values different from 100
Patch from Peter Teichmann
Currently, if the kernels HZ value is greater than 100, delays with the udelay function are too short. This can cause trouble for instance with the zd1201 usb wlan driver.
This patch suggests a solution that keeps the overhead small and maintains (hopefully) sufficient resolution.
Signed-off-by: Peter Teichmann
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/lib/delay.S b/arch/arm/lib/delay.S
index b3fb475..9183b06 100644
--- a/arch/arm/lib/delay.S
+++ b/arch/arm/lib/delay.S
@@ -9,28 +9,32 @@
*/
#include <linux/linkage.h>
#include <asm/assembler.h>
+#include <asm/param.h>
.text
.LC0: .word loops_per_jiffy
+.LC1: .word (2199023*HZ)>>11
/*
- * 0 <= r0 <= 2000
+ * r0 <= 2000
+ * lpj <= 0x01ffffff (max. 3355 bogomips)
+ * HZ <= 1000
*/
+
ENTRY(__udelay)
- mov r2, #0x6800
- orr r2, r2, #0x00db
+ ldr r2, .LC1
mul r0, r2, r0
-ENTRY(__const_udelay) @ 0 <= r0 <= 0x01ffffff
+ENTRY(__const_udelay) @ 0 <= r0 <= 0x7fffff06
ldr r2, .LC0
- ldr r2, [r2] @ max = 0x0fffffff
- mov r0, r0, lsr #11 @ max = 0x00003fff
- mov r2, r2, lsr #11 @ max = 0x0003ffff
+ 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
RETINSTR(moveq,pc,lr)
/*
- * loops = (r0 * 0x10c6 * 100 * loops_per_jiffy) / 2^32
+ * loops = r0 * HZ * loops_per_jiffy / 1000000
*
* Oh, if only we had a cycle counter...
*/