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

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Date:	Tue, 4 Dec 2012 09:32:12 +0800
From:	Haojian Zhuang <haojian.zhuang@...il.com>
To:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	mike.turquette@...aro.org
Cc:	Haojian Zhuang <haojian.zhuang@...il.com>
Subject: Re: [PATCH] clk: factor: calculate rate by do_div

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.
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