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

On Sun, 2018-12-30 at 18:50 +0100, LEROY Christophe wrote:

Arnd Bergmann [off-list ref] a écrit :

quoted

On Sat, Dec 29, 2018 at 3:51 AM Michael Schmitz
[off-list ref] wrote:

[...]

quoted

quoted

(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.

It's a preference, as with a lot of coding style stuff, which we leave
up to the maintainer.

That said, as has been pointed out, the current #ifdef has a failing
corner case when both are modular (because the code should then be
included).  The runtime macro that correctly expresses this is
IS_REACHABLE(CONFIG_NVRAM).

James