| Message ID | 20201213235447.138271-1-paul@crapouillou.net |
|---|---|
| State | Accepted |
| Commit | 1b399bb04837183cecdc1b32ef1cfc7fcfa75d32 |
| Headers | show |
| Series | [v2,1/2] kconfig.h: Add IF_ENABLED() macro | expand |
Hi, Le lun. 14 déc. 2020 à 10:05, Linus Walleij <linus.walleij@linaro.org> a écrit : > On Mon, Dec 14, 2020 at 12:54 AM Paul Cercueil <paul@crapouillou.net> > wrote: > >> IF_ENABLED(CONFIG_FOO, ptr) evaluates to (ptr) if CONFIG_FOO is set >> to 'y' >> or 'm', NULL otherwise. The (ptr) argument must be a pointer. >> >> The IF_ENABLED() macro can be very useful to help GCC drop dead >> code. > > I can apply this with the other patch to the pinctrl subsystem if > Arnd or > someone else who is good at KConfig provides an ACK. Arnd? Any feedback? Cheers, -Paul
On Mon, Jan 11, 2021 at 9:45 AM Paul Cercueil <paul@crapouillou.net> wrote: > > Hi, > > Le lun. 14 déc. 2020 à 10:05, Linus Walleij > <linus.walleij@linaro.org> a écrit : > > On Mon, Dec 14, 2020 at 12:54 AM Paul Cercueil <paul@crapouillou.net> > > wrote: > > > >> IF_ENABLED(CONFIG_FOO, ptr) evaluates to (ptr) if CONFIG_FOO is set > >> to 'y' > >> or 'm', NULL otherwise. The (ptr) argument must be a pointer. > >> > >> The IF_ENABLED() macro can be very useful to help GCC drop dead > >> code. Looks great! Thanks a lot for getting this sorted. > > I can apply this with the other patch to the pinctrl subsystem if > > Arnd or someone else who is good at KConfig provides an ACK. Yes, please do. Acked-by: Arnd Bergmann <arnd@arndb.de>
Both patches applied! Yours, Linus Walleij
diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h index 9d12c970f18f..e78e17a76dc9 100644 --- a/include/linux/kconfig.h +++ b/include/linux/kconfig.h @@ -72,4 +72,10 @@ */ #define IS_ENABLED(option) __or(IS_BUILTIN(option), IS_MODULE(option)) +/* + * IF_ENABLED(CONFIG_FOO, ptr) evaluates to (ptr) if CONFIG_FOO is set to 'y' + * or 'm', NULL otherwise. + */ +#define IF_ENABLED(option, ptr) (IS_ENABLED(option) ? (ptr) : NULL) + #endif /* __LINUX_KCONFIG_H */
IF_ENABLED(CONFIG_FOO, ptr) evaluates to (ptr) if CONFIG_FOO is set to 'y' or 'm', NULL otherwise. The (ptr) argument must be a pointer. The IF_ENABLED() macro can be very useful to help GCC drop dead code. For instance, consider the following: #ifdef CONFIG_FOO_SUSPEND static int foo_suspend(struct device *dev) { ... } #endif static struct pm_ops foo_ops = { #ifdef CONFIG_FOO_SUSPEND .suspend = foo_suspend, #endif }; While this works, the foo_suspend() macro is compiled conditionally, only when CONFIG_FOO_SUSPEND is set. This is problematic, as there could be a build bug in this function, we wouldn't have a way to know unless the config option is set. An alternative is to declare foo_suspend() always, but mark it as maybe unused: static int __maybe_unused foo_suspend(struct device *dev) { ... } static struct pm_ops foo_ops = { #ifdef CONFIG_FOO_SUSPEND .suspend = foo_suspend, #endif }; Again, this works, but the __maybe_unused attribute is required to instruct the compiler that the function may not be referenced anywhere, and is safe to remove without making a fuss about it. This makes the programmer responsible for tagging the functions that can be garbage-collected. With this patch, it is now possible to write the following: static int foo_suspend(struct device *dev) { ... } static struct pm_ops foo_ops = { .suspend = IF_ENABLED(CONFIG_FOO_SUSPEND, foo_suspend), }; The foo_suspend() function will now be automatically dropped by the compiler, and it does not require any specific attribute. Signed-off-by: Paul Cercueil <paul@crapouillou.net> --- Notes: v2: Only add IF_ENABLED() and don't verify that the argument is a pointer; since the second argument of the ?: ternary operator is NULL, the compiler should issue an error if the other argument is not a pointer. include/linux/kconfig.h | 6 ++++++ 1 file changed, 6 insertions(+)