root/arch/arm/lib/delay-loop.S

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /*
   3  *  linux/arch/arm/lib/delay.S
   4  *
   5  *  Copyright (C) 1995, 1996 Russell King
   6  */
   7 #include <linux/linkage.h>
   8 #include <asm/assembler.h>
   9 #include <asm/delay.h>
  10 
  11                 .text
  12 
  13 .LC0:           .word   loops_per_jiffy
  14 .LC1:           .word   UDELAY_MULT
  15 
  16 /*
  17  * loops = r0 * HZ * loops_per_jiffy / 1000000
  18  *
  19  * r0  <= 2000
  20  * HZ  <= 1000
  21  */
  22 
  23 ENTRY(__loop_udelay)
  24                 ldr     r2, .LC1
  25                 mul     r0, r2, r0              @ r0 = delay_us * UDELAY_MULT
  26 ENTRY(__loop_const_udelay)                      @ 0 <= r0 <= 0xfffffaf0
  27                 ldr     r2, .LC0
  28                 ldr     r2, [r2]
  29                 umull   r1, r0, r2, r0          @ r0-r1 = r0 * loops_per_jiffy
  30                 adds    r1, r1, #0xffffffff     @ rounding up ...
  31                 adcs    r0, r0, r0              @ and right shift by 31
  32                 reteq   lr
  33 
  34                 .align 3
  35 
  36 @ Delay routine
  37 ENTRY(__loop_delay)
  38                 subs    r0, r0, #1
  39 #if 0
  40                 retls   lr
  41                 subs    r0, r0, #1
  42                 retls   lr
  43                 subs    r0, r0, #1
  44                 retls   lr
  45                 subs    r0, r0, #1
  46                 retls   lr
  47                 subs    r0, r0, #1
  48                 retls   lr
  49                 subs    r0, r0, #1
  50                 retls   lr
  51                 subs    r0, r0, #1
  52                 retls   lr
  53                 subs    r0, r0, #1
  54 #endif
  55                 bhi     __loop_delay
  56                 ret     lr
  57 ENDPROC(__loop_udelay)
  58 ENDPROC(__loop_const_udelay)
  59 ENDPROC(__loop_delay)