linux-kernel - Re: [Nouveau] [PATCH] [RESEND] drm/nouveau/clk: fix gcc-7 -Wint-in-bool-context warning

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Message-ID: <CAEXux-YrqdiGPxkzPUdLxVS7kW1Q-x0KhibA=NGy3Hzm49tb_w@mail.gmail.com>
Date:   Wed, 6 Sep 2017 22:15:48 +0200
From:   Karol Herbst <karolherbst@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Ben Skeggs <bskeggs@...hat.com>, David Airlie <airlied@...ux.ie>,
        ML nouveau <nouveau@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Nouveau] [PATCH] [RESEND] drm/nouveau/clk: fix gcc-7
 -Wint-in-bool-context warning

On Wed, Sep 6, 2017 at 10:11 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Wed, Sep 6, 2017 at 4:20 PM, Karol Herbst <karolherbst@...il.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