linux-kernel - Re: [PATCH v8 01/25] scsi/atari_scsi: Don't select CONFIG

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Date:   Sun, 30 Dec 2018 18:50:02 +0100
From:   LEROY Christophe <christophe.leroy@....fr>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Finn Thain <fthain@...egraphics.com.au>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        Michael Schmitz <schmitzmic@...il.com>
Subject: Re: [PATCH v8 01/25] scsi/atari_scsi: Don't select CONFIG_NVRAM

Arnd Bergmann <arnd@...db.de> a écrit :

> On Sat, Dec 29, 2018 at 3:51 AM Michael Schmitz <schmitzmic@...il.com> wrote:
>>
>> Hi Finn,
>>
>> Am 29.12.2018 um 15:34 schrieb Finn Thain:
>> > On Sat, 29 Dec 2018, Michael Schmitz wrote:
>> >
>> >>
>> >> IS_BUILTIN(CONFIG_NVRAM) is probably what Christophe really  
>> meant to suggest.
>> >>
>> >> Or (really going out on a limb here):
>> >>
>> >> IS_BUILTIN(CONFIG_NVRAM) ||
>> >> ( IS_MODULE(CONFIG_ATARI_SCSI) && IS_ENABLED(CONFIG_NVRAM) )
>> >>
>> >> Not that I'd advocate that, for this series.
>> >>
>> >
>> > Well, you are a maintainer for atari_scsi.c.
>> >
>> > Are you saying that you want IS_BUILTIN(CONFIG_NVRAM) used here instead of
>> > ifdef?
>>
>> No, just pointing out that there would be a way to avoid the ifdef
>> without messing up driver behaviour. I'm fine with the ifdef - not least
>> because it clearly eliminates code that would be unreachable.
>>
>> (On second thought - I don't want to speculate whether there's weird
>> compiler options that could result in the nvram_check_checksum and
>> nvram_read_bytes symbols to still be referenced in the final link, even
>> though IS_BUILTIN(CONFIG_NVRAM) always evaluates to false. Best leave
>> this as-is.)
>
> As far as I know, it's totally reliable with the supported compilers  
> (gcc-4.6+).
> In the older compilers (e.g. 4.1), there was a corner case, where it could
> have failed to eliminate a function that was only referenced through  
> a pointer
> from a discarded variable, but a plain IS_ENABLED() check like the one here
> was still ok, and lots of code relies on that.
>
> Other than that, I agree either way is totally fine here, so no objections
> to using the #ifdef.

As far as I know, kernel codying style promotes the use of  
IS_ENABLED() etc. instead of #ifdefs when possible.

Christophe

>
>       Arnd