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

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Date:	Sun, 16 Dec 2012 14:27:58 +0800
From:	Haojian Zhuang <haojian.zhuang@...il.com>
To:	Mike Turquette <mturquette@...aro.org>
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 Sun, Dec 16, 2012 at 4:54 AM, Mike Turquette <mturquette@...aro.org> wrote:
> 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

It's nice. Thank you.

Best Regards
Haojian
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