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

[LEROY Christophe]

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):
> > >>
> > >> 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