linux-kernel - RE: [PATCH] clk:Fix divide by 0 error in divider_ro_round_rate

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Date:   Sat, 30 Mar 2019 02:03:54 +0000
From:   Nixiaoming <nixiaoming@...wei.com>
To:     Stephen Boyd <sboyd@...nel.org>,
        "jbrunet@...libre.com" <jbrunet@...libre.com>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "rnayak@...com" <rnayak@...com>,
        "sboyd@...eaurora.org" <sboyd@...eaurora.org>,
        "soren.brinkmann@...inx.com" <soren.brinkmann@...inx.com>
CC:     "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] clk:Fix divide by 0 error in
 divider_ro_round_rate_parent

On 3/30/2019 6:42 AM Stephen Boyd wrote:
>Quoting nixiaoming (2019-03-29 02:05:24)
>> In the function divider_recalc_rate The judgment of the return value of
>
>Please write divider_recalc_rate() with parenthesis to show it's a
>function.
>
>> _get_div indicates that the return value of _get_div may be 0.
>
>__get_div()
Thank you for your guidance, I will correct it later in the patch.

>> In order to avoid the divide-by-zero error, add check the return value
>> of _get_div in the divider_ro_round_rate_parent
>> 
>> Signed-off-by: nixiaoming <nixiaoming@...wei.com>
>
>Is this your name? nixiaoming? Or is it written some other way?

Chinese name 倪小明
>> ---
>>  drivers/clk/clk-divider.c | 2 ++
>>  1 file changed, 2 insertions(+)
>> 
>> diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
>> index e5a1726..0854e3e 100644
>> --- a/drivers/clk/clk-divider.c
>> +++ b/drivers/clk/clk-divider.c
>> @@ -347,6 +347,8 @@ long divider_ro_round_rate_parent(struct clk_hw *hw, struct clk_hw *parent,
>>         int div;
>>  
>>         div = _get_div(table, val, flags, width);
>> +       if (!div) /* avoid divide-by-zero */
>> +               return -EINVAL;
>
>How does _get_div() return 0? What is the value of 'flags' here when
>this goes wrong?

divider_ro_round_rate_parent() and divider_recalc_rate() are functions
 of the EXPORT_SYMBOL_GPL attribute

If _get_div() can return 0 in the argument of divider_recalc_rate()
Then should be able to return 0 in divider_ro_round_rate_parent()

>
>>  
>>         /* Even a read-only clock can propagate a rate change */
>>         if (clk_hw_get_flags(hw) & CLK_SET_RATE_PARENT) {
>> -- 
>> 1.8.5.6
>> 
>
>Wow that's a 5 year old version of git!
>
>