linux-kernel - Re: [PATCH] clk: factor: calculate rate by do

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Date:	Sat, 15 Dec 2012 12:54:01 -0800
From:	Mike Turquette <mturquette@...aro.org>
To:	Haojian Zhuang <haojian.zhuang@...il.com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Bergmann Arnd <arnd@...db.de>
Subject: Re: [PATCH] clk: factor: calculate rate by do_div

On Sat, Dec 15, 2012 at 8:41 AM, Haojian Zhuang
<haojian.zhuang@...il.com> wrote:
> On Tue, Dec 4, 2012 at 9:32 AM, Haojian Zhuang <haojian.zhuang@...il.com> wrote:
>> On Mon, Dec 3, 2012 at 4:14 PM, Haojian Zhuang <haojian.zhuang@...il.com> wrote:
>>> clk->rate = parent->rate / div * mult
>>>
>>> The formula is OK. But it may overflow while we do operate with
>>> unsigned long. So use do_div instead.
>>>
>>> Signed-off-by: Haojian Zhuang <haojian.zhuang@...il.com>
>>> ---
>>>  drivers/clk/clk-fixed-factor.c |    5 ++++-
>>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/clk/clk-fixed-factor.c b/drivers/clk/clk-fixed-factor.c
>>> index a489985..1ef271e 100644
>>> --- a/drivers/clk/clk-fixed-factor.c
>>> +++ b/drivers/clk/clk-fixed-factor.c
>>> @@ -28,8 +28,11 @@ static unsigned long clk_factor_recalc_rate(struct clk_hw *hw,
>>>                 unsigned long parent_rate)
>>>  {
>>>         struct clk_fixed_factor *fix = to_clk_fixed_factor(hw);
>>> +       unsigned long long int rate;
>>>
>>> -       return parent_rate * fix->mult / fix->div;
>>> +       rate = (unsigned long long int)parent_rate * fix->mult;
>>> +       do_div(rate, fix->div);
>>> +       return (unsigned long)rate;
>>>  }
>>>
>>>  static long clk_factor_round_rate(struct clk_hw *hw, unsigned long rate,
>>> --
>>> 1.7.10.4
>>>
>>
>> Correct Mike's email address.
>
> Any comments? Does it mean that nobody want to fix the bug?

Thanks for the patch.  My apologies for letting this one slip through
the cracks but my normal email workflow was unavoidably disrupted and
I find myself playing catch-up with pending patches.

The patch looks good to me but I'll change the $SUBJECT to "clk:
fixed-factor: round_rate should use do_div" and do some testing before
taking it in.

Regards,
Mike
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