Nouveau - Sep 2017 - [PATCH] [RESEND] drm/nouveau/clk: fix gcc-7 -Wint-in-bool-context warning

On Wed, Sep 6, 2017 at 4:20 PM, Karol Herbst <karolherbst at gmail.com>
wrote:
>> In this instance, I think using multiplication is more intuitive
>> than '&&', so I'm adding a comparison to zero
instead to shut up
>> the warning. To further improve readability, I also make the
>> error case indented and leave the normal case as the final
'return'
>> statement.
>>
>
> I think to make perfectly clear why this check is done, we simply
> should precompute the denominator and do something like this:
>
> int denominator = M * P
> if (denominator == 0)
>    return 0;
> return sclk * N / denominator;
>
> but with a better name for "denominator".
I don't know what M and P actually are in this function, so I couldn't
come up with a much better name either, how about simply 'divisor'?
> I even imagine, that there
> are some macros in the kernel for dealing with something like this
> already, so that we could do instead:
>
> return AWESOME_DIV_MACRO(sclk * N, M * P)
I don't think that exists, the behavior for divide-by-zero really
depends a lot on the context, and returning zero is probably
often not a good solution.

      Arnd

On Wed, Sep 6, 2017 at 10:11 PM, Arnd Bergmann <arnd at arndb.de>
wrote:
> On Wed, Sep 6, 2017 at 4:20 PM, Karol Herbst <karolherbst at
gmail.com> wrote:
>>> In this instance, I think using multiplication is more intuitive
>>> than '&&', so I'm adding a comparison to zero
instead to shut up
>>> the warning. To further improve readability, I also make the
>>> error case indented and leave the normal case as the final
'return'
>>> statement.
>>>
>>
>> I think to make perfectly clear why this check is done, we simply
>> should precompute the denominator and do something like this:
>>
>> int denominator = M * P
>> if (denominator == 0)
>>    return 0;
>> return sclk * N / denominator;
>>
>> but with a better name for "denominator".
>
> I don't know what M and P actually are in this function, so I
couldn't
> come up with a much better name either, how about simply 'divisor'?
>
what about "MP"? M and P are simply dividers for the PLL configuration
and there are two of them. I think "P" is the post divider.
>> I even imagine, that there
>> are some macros in the kernel for dealing with something like this
>> already, so that we could do instead:
>>
>> return AWESOME_DIV_MACRO(sclk * N, M * P)
>
> I don't think that exists, the behavior for divide-by-zero really
> depends a lot on the context, and returning zero is probably
> often not a good solution.
>
>       Arnd

On Wed, Sep 6, 2017 at 10:15 PM, Karol Herbst <karolherbst at gmail.com>
wrote:
> On Wed, Sep 6, 2017 at 10:11 PM, Arnd Bergmann <arnd at arndb.de>
wrote:
>>> but with a better name for "denominator".
>>
>> I don't know what M and P actually are in this function, so I
couldn't
>> come up with a much better name either, how about simply
'divisor'?
>>
>
> what about "MP"? M and P are simply dividers for the PLL
configuration
> and there are two of them. I think "P" is the post divider.
>
Fine with me. That was actually what I initially did after your reply and
then changed it to divisor. I've changed it back now and sent the new
version.

      Arnd