I found that our MIPS compatible CPU VR has unique instruction - 'STANDBY'.
And other CPU which designed for PDA have their  own instruction similarly.
(Please see #ifdef VR41_STANDBY_IDLE in arch/mips/mips/locore.S)

Thereby I want to select idle routine on booting dynamically.

I 've made a patch. Please review and comment.

------ BEGIN
RCS file: /cvsroot/syssrc/sys/arch/mips/mips/locore.S,v
retrieving revision 1.84
diff -r1.84 locore.S
262c262
< LEAF(idle)
---
> LEAF(mips_idle)
288c288,293
< END(idle)
---
> END(mips_idle)
>
> .data
> _C_LABEL(idle):
>       .word   mips_idle
> .text
318c323,328
<       beq     t1, zero, _C_LABEL(idle)
---
>       bne     t1, zero, 1f
>       la      t2, _C_LABEL(idle)
>       lw      t2, (t2)
>       jal     ra, t2
>       nop
> 1:
331c341,346
<       beq     t0, zero, _C_LABEL(idle)        # if none, idle
---
>       bne     t0, zero, 1f
>       la      t3, _C_LABEL(idle)
>       lw      t3, (t3)
>       jal     ra, t3
>       nop
> 1:
------ END