[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>

1 files changed, 12 insertions, 8 deletions

diff --git a/arch/arm/lib/delay.S b/arch/arm/lib/delay.S
index b3fb475b412..9183b06c0e2 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...
  */