ARM: 8619/1: udelay: document the various constants
Explain where the value for UDELAY_MULT and UDELAY_SHIFT come from.
Also fix/clarify some comments pertaining to their usage in the
assembly code.
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/lib/delay-loop.S b/arch/arm/lib/delay-loop.S
index 792c59d..c766694 100644
--- a/arch/arm/lib/delay-loop.S
+++ b/arch/arm/lib/delay-loop.S
@@ -17,24 +17,23 @@
.LC1: .word UDELAY_MULT
/*
+ * loops = r0 * HZ * loops_per_jiffy / 1000000
+ *
* r0 <= 2000
* HZ <= 1000
*/
ENTRY(__loop_udelay)
ldr r2, .LC1
- mul r0, r2, r0
-ENTRY(__loop_const_udelay) @ 0 <= r0 <= 0x7fffff06
+ mul r0, r2, r0 @ r0 = delay_us * UDELAY_MULT
+ENTRY(__loop_const_udelay) @ 0 <= r0 <= 0xfffffaf0
ldr r2, .LC0
ldr r2, [r2]
- umull r1, r0, r2, r0
- adds r1, r1, #0xffffffff
- adcs r0, r0, r0
+ umull r1, r0, r2, r0 @ r0-r1 = r0 * loops_per_jiffy
+ adds r1, r1, #0xffffffff @ rounding up ...
+ adcs r0, r0, r0 @ and right shift by 31
reteq lr
-/*
- * loops = r0 * HZ * loops_per_jiffy / 1000000
- */
.align 3
@ Delay routine