On Mon, 5 Dec 2011, Paul Walmsley wrote:

For example, here's a trivial implementation for rate recalculation for a 
integer divider clock node (that can't be handled with a right shift):

s64 div(struct clk *clk, u32 div) {
	if (clk->flags & CLK_PARENT_RATE_MAX_U32)
		return ((u32)(clk->parent->rate & 0xffffffff)) / div;

	clk->rate = clk->parent->rate;
	do_div(clk->rate, div);
	return clk->rate;
}

(removing some useless cruft from the above function, for clarity's sake)

s64 div(struct clk *clk, u32 div) {
	s64 r;

	if (clk->flags & CLK_PARENT_RATE_MAX_U32)
		return ((u32)clk->parent->rate) / div;

	r = clk->parent->rate;
	do_div(r, div);
	return r;
}

00000000 <div>:
   0:	e92d4010 	push	{r4, lr}
   4:	e1a04001 	mov	r4, r1
   8:	e5d03010 	ldrb	r3, [r0, #16]
   c:	e3130001 	tst	r3, #1
  10:	1a000005 	bne	2c <div+0x2c>

  14:	e5903000 	ldr	r3, [r0]
  18:	e1c300d8 	ldrd	r0, [r3, #8]
  1c:	ebfffffe 	bl	0 <__do_div64>
  20:	e1a00002 	mov	r0, r2
  24:	e1a01003 	mov	r1, r3
  28:	e8bd8010 	pop	{r4, pc}

  2c:	e5900000 	ldr	r0, [r0]
  30:	e5900008 	ldr	r0, [r0, #8]
  34:	ebfffffe 	bl	0 <__aeabi_uidiv>
  38:	e3a01000 	mov	r1, #0
  3c:	e8bd8010 	pop	{r4, pc}


- Paul