2011/4/27 Michael Hope <michael.h...@linaro.org>:
> On Tue, Apr 26, 2011 at 1:48 PM, Barry Song <21cn...@gmail.com> wrote:
>> 2011/4/26 Barry Song <21cn...@gmail.com>:
>>> Hi Michael,
>>>
>>> 2011/4/26 Michael Hope <michael.h...@linaro.org>:
>>>> Hi Barry. I think the toolchain is operating correctly here. The
>>>> current version recognises a divide followed by a modulo and optimises
>>>> this into a call to the standard EABI function __aeabi__uldivmod().
>>>> Note the code:
>>>>
>>>> do_div(Kpart, source);
>>>>
>>>> K = Kpart & 0xFFFFFFFF;
>>>>
>>>> /* Check if we need to round */
>>>> if ((K % 10) >= 5)
>>>> K += 5;
>>>>
>>>> This function is provided by libgcc for normal applications. The
>>>> kernel provides it's own versions in arch/arm/lib/lib1funcs.s but is
>>>> missing __aeabi_uldivmod (note the 'l' for 64 bit).
>>> In fact the problem happen ealier:
>>>
>>> if (Ndiv < 6) {
>>> source /= 2;
>>> pll_div->pre_div = 1;
>>> Ndiv = target / source;
>>> } else
>>> pll_div->pre_div = 0;
>>>
>>> if ((Ndiv < 6) || (Ndiv > 12))
>>> printk(KERN_WARNING
>>> "WM8974 N value %u outwith recommended range!\n",
>>> Ndiv);
>>>
>>> pll_div->n = Ndiv;
>>> Nmod = target % source;
>>> Kpart = FIXED_PLL_SIZE * (long long)Nmod;
>>>
>>> do_div(Kpart, source);
>>>
>>> If commenting "source /= 2", the problem disappear.
>>>
>>>
>> Or if adding one line before do_div, all will be ok.
>> asm("" : "+r"(source));
>> do_div(Kpart, source);
>
> Hi Barry. I can reproduce the problem in Linaro GCC 4.5-2011.04 and
> GCC 4.5.2. It does not exist in GCC 4.6.0. wm8974_set_dai_pll()
> inlines the call to pll_factors() and leaves a .globl reference to
> __aeabi_uldivmod in the code. This function is never called.
>
> Marking pll_factors() as __attribute__((noinline)) also works around
> the problem.
>
> I've logged http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48783 upstream
> and recorded this as LP: #771551.
Thanks. I am totally thinking it is a gcc bug not an optimization
feature. in fact, __aeabi_uldivmod is never called as seen by objdump.
It only exists in symbol reference list.
>
> -- Michael
>
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