Re: [PATCH v8 01/25] scsi/atari_scsi: Don't select CONFIG_NVRAM

From: LEROY Christophe
Date: Sun Dec 30 2018 - 12:50:10 EST

Arnd Bergmann <arnd@xxxxxxxx> a ÃcritÂ:

On Sat, Dec 29, 2018 at 3:51 AM Michael Schmitz <schmitzmic@xxxxxxxxx> 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):
>> 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.