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| author | Nicolas Pitre <nicolas.pitre@linaro.org> | 2016-10-07 05:38:35 +0100 |
|---|---|---|
| committer | Russell King <rmk+kernel@armlinux.org.uk> | 2016-10-19 10:52:36 +0100 |
| commit | 207b1150c00d0471c11669cd3f249d81909b3ac8 (patch) | |
| tree | 15b52a6047ac5b4c86f5bd079841f777f3377ffd /arch/arm/lib | |
| parent | 1001354ca34179f3db924eb66672442a173147dc (diff) | |
| download | linux-207b1150c00d0471c11669cd3f249d81909b3ac8.tar.gz | |
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>
Diffstat (limited to 'arch/arm/lib')
| -rw-r--r-- | arch/arm/lib/delay-loop.S | 15 |
1 files changed, 7 insertions, 8 deletions
diff --git a/arch/arm/lib/delay-loop.S b/arch/arm/lib/delay-loop.S index 792c59d885bc..c766694e929c 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 |