linux-kernel - RE: [PATCH] clk: imx: use div64_u64() instead of do

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Message-ID: <4f0336b0217f4e7fa9a1a7aa044ee4fe@AcuMS.aculab.com>
Date:   Wed, 9 Feb 2022 22:21:35 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Qing Wang' <wangqing@...o.com>, Abel Vesa <abel.vesa@....com>,
        "Michael Turquette" <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        "Shawn Guo" <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] clk: imx: use div64_u64() instead of do_div()

From: Qing Wang <wangqing@...o.com>
> Sent: 09 February 2022 08:37
> 
> From: Wang Qing <wangqing@...o.com>
> 
> do_div() does a 64-by-32 division.
> When the divisor is u64, do_div() truncates it to 32 bits, this means it
> can test non-zero and be truncated to zero for division.

What is the domain of parent_rate?

Unless it can exceed 2^32 do_div() is correct.
Ignore checkpatch.

> 
> fix do_div.cocci warning:
> WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead.
> 
> Signed-off-by: Wang Qing <wangqing@...o.com>
> ---
>  drivers/clk/imx/clk-frac-pll.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/imx/clk-frac-pll.c b/drivers/clk/imx/clk-frac-pll.c
> index c703056..90b25e3
> --- a/drivers/clk/imx/clk-frac-pll.c
> +++ b/drivers/clk/imx/clk-frac-pll.c
> @@ -129,11 +129,11 @@ static long clk_pll_round_rate(struct clk_hw *hw, unsigned long rate,
>  	parent_rate *= 8;
>  	rate *= 2;
>  	temp64 = rate;
> -	do_div(temp64, parent_rate);
> +	div64_u64(temp64, parent_rate);
>  	divfi = temp64;
>  	temp64 = rate - divfi * parent_rate;
>  	temp64 *= PLL_FRAC_DENOM;
> -	do_div(temp64, parent_rate);
> +	div64_u64(temp64, parent_rate);
>  	divff = temp64;
> 
>  	temp64 = parent_rate;
> --
> 2.7.4

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