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

[Arnd Bergmann]

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):
> >>
> >> 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.

      Arnd