linux-kernel - Re: [PATCH 3/4] scsi: fix compiler warning for sg

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Date:	Thu, 5 Nov 2015 20:07:03 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Sinan Kaya <okaya@...eaurora.org>
Cc:	linux-scsi <linux-scsi@...r.kernel.org>, timur@...eaurora.org,
	cov@...eaurora.org, jcm@...hat.com,
	Doug Gilbert <dgilbert@...erlog.com>,
	"James E.J. Bottomley" <JBottomley@...n.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] scsi: fix compiler warning for sg

On Thu, Nov 5, 2015 at 5:10 PM, Sinan Kaya <okaya@...eaurora.org> wrote:
>
>
> On 11/5/2015 3:48 AM, Andy Shevchenko wrote:
>>
>> On Thu, Nov 5, 2015 at 6:46 AM, Sinan Kaya <okaya@...eaurora.org> wrote:
>>>
>>> The MULDIV macro has been designed for small
>>> numbers. It emits an overflow warning on 64 bit
>>> systems. This patch places type casts in the
>>> parameters to fix the compiler warning.
>>>
>>> Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
>>> ---
>>>   drivers/scsi/sg.c | 5 ++++-
>>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
>>> index 9d7b7db..eb2739d 100644
>>> --- a/drivers/scsi/sg.c
>>> +++ b/drivers/scsi/sg.c
>>> @@ -88,7 +88,10 @@ static void sg_proc_cleanup(void);
>>>    * Of course an overflow is inavoidable if the result of muldiv doesn't
>>> fit
>>>    * in 32 bits.
>>>    */
>>> -#define MULDIV(X,MUL,DIV) ((((X % DIV) * MUL) / DIV) + ((X / DIV) *
>>> MUL))
>>> +static inline u64 MULDIV(u64 X, u32 MUL, u32 DIV)
>>> +{
>>> +       return ((((X % DIV) * MUL) / DIV) + ((X / DIV) * MUL));
>>> +}
>>
>>
>> Like kbuild bot already told you it would be nice to think of 32-bit
>> architectures.
>>
>> Moreover we have mult_frac() macro already for 32-bit numbers.
>>
>> For 64 bit numbers you need to do do_div().
>>
>> Like:
>>
>> static inline u64 mult_frac64(u64 x, u32 m, u32 n)
>> {
>> u64 ret;
>>
>> ret = do_div(x, n);
>> return ret * m;
>> }
>>
>
> OK, I didn't know that we had such a macro. To make this look like the other
> macro, I can do this.
>
> static inline u64 mult_frac64(u64 x, u32 numer, u32 denom)
> {
>         u64 quot;
>         u64 rem  = x % denom;
>         u64 rem2;
>
>         quot = x;
>         do_div(quot, denom);
>
>         rem2 = rem * numer;
>         do_div(rem2, denom);
>
>         return (quot * numer) + rem2;
> }

Might be I did a wrong smaple, but do_div() returns two values actually.
You perhaps overlooked it and thus wrote something redundant above.

>
> #define MULDIV(X,MUL,DIV)       mult_frac64(X, MUL, DIV)
>
>>
>>>
>>>   #define SG_DEFAULT_TIMEOUT MULDIV(SG_DEFAULT_TIMEOUT_USER, HZ, USER_HZ)
>>>
>>> --
>>> Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
>>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
>>> Linux Foundation Collaborative Project
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
>>> the body of a message to majordomo@...r.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>>
>>
>>
>
> --
> Sinan Kaya
> Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
> Foundation Collaborative Project



-- 
With Best Regards,
Andy Shevchenko
--
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