linux-kernel - Re: [PATCH] net: davinci: fix building davinci mdio code without CONFIG

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Date:   Tue, 29 May 2018 16:31:19 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Sekhar Nori <nsekhar@...com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Florian Fainelli <f.fainelli@...il.com>,
        linux-omap <linux-omap@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: davinci: fix building davinci mdio code without CONFIG_OF

On Tue, May 29, 2018 at 3:25 PM, Sekhar Nori <nsekhar@...com> wrote:

>> @@ -374,7 +372,7 @@ static int davinci_mdio_probe(struct platform_device *pdev)
>>               return -ENOMEM;
>>       }
>>
>> -     if (dev->of_node) {
>> +     if (IS_ENABLED(CONFIG_OF) && dev->of_node) {
>>               const struct of_device_id       *of_id;
>>
>>               ret = davinci_mdio_probe_dt(&data->pdata, pdev);
>
> I was expecting this one change to fix the issue since the if() block
> should be compiled away removing references to davinci_mdio_probe_dt().
>
> The code does get compiled out and there are no references to
> davinci_mdio_probe_dt() in the final object when !CONFIG_OF.
>
> But the compile error remains if the #ifdefs you removed above are
> installed back. Not sure why.

The way that "if (IS_ENABLED())" works, everything gets compiled at
first, but then the compiler uses dead code elimination to remove it
from the output after verifying that everything builds.

       Arnd