linux-kernel - Re: [PATCH] mmc: mtk-sd: use div64_u64() instead of do

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Message-ID: <bcd6688f-6f42-ca8f-ab9c-978eeff4f4e3@wanadoo.fr>
Date:   Thu, 17 Feb 2022 21:00:56 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Ulf Hansson <ulf.hansson@...aro.org>, Qing Wang <wangqing@...o.com>
Cc:     Chaotian Jing <chaotian.jing@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-mmc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mmc: mtk-sd: use div64_u64() instead of do_div()

Le 17/02/2022 à 16:39, Ulf Hansson a écrit :
> On Wed, 9 Feb 2022 at 09:39, Qing Wang <wangqing@...o.com> wrote:
>>
>> 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.
>>
>> fix do_div.cocci warning:
>> do_div() does a 64-by-32 division, please consider using div64_u64 instead.
>>
>> Signed-off-by: Wang Qing <wangqing@...o.com>
> 
> Applied for next, thanks!


This is wrong.

See [1].


Wang Qing, you should really warn all the people you have sent such patches.

CJ

[1]: 
https://lore.kernel.org/linux-kernel/19b96972-cee7-937f-21ce-c78982ed2048@linaro.org/


> 
> Kind regards
> Uffe
> 
> 
>> ---
>>   drivers/mmc/host/mtk-sd.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/mmc/host/mtk-sd.c b/drivers/mmc/host/mtk-sd.c
>> index 65037e1..777c9a8
>> --- a/drivers/mmc/host/mtk-sd.c
>> +++ b/drivers/mmc/host/mtk-sd.c
>> @@ -766,7 +766,7 @@ static u64 msdc_timeout_cal(struct msdc_host *host, u64 ns, u64 clks)
>>                  clk_ns  = 1000000000ULL;
>>                  do_div(clk_ns, mmc->actual_clock);
>>                  timeout = ns + clk_ns - 1;
>> -               do_div(timeout, clk_ns);
>> +               div64_u64(timeout, clk_ns);
>>                  timeout += clks;
>>                  /* in 1048576 sclk cycle unit */
>>                  timeout = DIV_ROUND_UP(timeout, BIT(20));
>> --
>> 2.7.4
>>
>