linux-kernel - Re: [PATCH] clk:mmp: clk-mix.c fix divide-by-zero

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Message-ID: <155389969479.20095.682832622477946593@swboyd.mtv.corp.google.com>
Date:   Fri, 29 Mar 2019 15:48:14 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     chao.xie@...vell.com, mturquette@...libre.com,
        nixiaoming@...wei.com
Cc:     linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk:mmp: clk-mix.c fix divide-by-zero

Quoting nixiaoming (2019-03-29 04:46:00)
> The _get_div function has a branch with a return value of 0
> Add a check on the return value of _get_div to avoid divide-by-zero
> 
> Signed-off-by: nixiaoming <nixiaoming@...wei.com>

Similar questions apply here as they do on the generic divider patch you
sent.

> ---
>  drivers/clk/mmp/clk-mix.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/clk/mmp/clk-mix.c b/drivers/clk/mmp/clk-mix.c
> index 90814b2..9d152c2 100644
> --- a/drivers/clk/mmp/clk-mix.c
> +++ b/drivers/clk/mmp/clk-mix.c
> @@ -245,6 +245,8 @@ static int mmp_clk_mix_determine_rate(struct clk_hw *hw,
>                         div_val_max = _get_maxdiv(mix);
>                         for (j = 0; j < div_val_max; j++) {
>                                 div = _get_div(mix, j);
> +                               if (!div) /* avoid divide-by-zero */

Why can't we return 1 for the divider value here?

> +                                       continue;
>                                 mix_rate = parent_rate / div;
>                                 gap = abs(mix_rate - req->rate);
>                                 if (!parent_best || gap < gap_best) {
> @@ -341,6 +343,8 @@ static unsigned long mmp_clk_mix_recalc_rate(struct clk_hw *hw,
>         shift = mix->reg_info.shift_div;
>  
>         div = _get_div(mix, MMP_CLK_BITS_GET_VAL(mux_div, width, shift));
> +       if (!div) /* avoid divide-by-zero */

Same question.

> +               return -EINVAL;
>  
>         return parent_rate / div;
>  }