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

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Date:   Wed, 6 Sep 2017 22:11:44 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Karol Herbst <karolherbst@...il.com>
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 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'?

> 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