On Sun, 19 Feb 2023 12:36:28 +0100
Heinrich Schuchardt <heinrich.schucha...@canonical.com> wrote:
Hi,
> We want to move from using #ifdef to using if in our code. A lot of our
> code using #ifdef is structured like:
>
> #ifdef CONFIG_FOO
> fun(CONFIG_FOO_OPT);
> #endif
>
> In Kconfig you will find
>
> config FOO
> bool "enable foo"
>
> config FOO_OPT
> string "value for foo"
> depends on FOO
>
> We cannot use CONFIG_FOO_OPT in our code directly if CONFIG_FOO is not
> defined.
>
> if (IS_ENABLED(CONFIG_FOO)
> fun(CONFIG_FOO_OPT);
>
> This would result in an error due to the undefined symbol CONFIG_FOO_OPT.
>
> The new macro IF_ENABLED(CONFIG_FOO, opt_cfg, def_val) which evaluates
> to opt_cfg if CONFIG_FOO is set to 'y' and to def_val otherwise comes to
> the rescue:
>
> if (IS_ENABLED(CONFIG_FOO)
> fun(IF_ENABLED(CONFIG_FOO, CONFIG_FOO_OPT, "");
Ah, yeah, I like this one, this is indeed the most common pattern that
prevents many "#if to if" conversions.
I briefly thought about unifying those two lines, but it's probably
limiting, as it appears more flexible this way:
>
> If CONFIG_FOO is not defined, the compiler will see
>
> if (0)
> fun("");
>
> and be happy.
>
> If CONFIG_FOO is defined, the compiler will see
>
> if (1)
> fun(CONFIG_FOO_OPT)
>
> and be equally happy.
>
> Signed-off-by: Heinrich Schuchardt <heinrich.schucha...@canonical.com>
Reviewed-by: Andre Przywara <andre.przyw...@arm.com>
Cheers,
Andre
> ---
> v3:
> new patch
> ---
> include/linux/kconfig.h | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h
> index 2bc704e110..7fea72da1a 100644
> --- a/include/linux/kconfig.h
> +++ b/include/linux/kconfig.h
> @@ -28,6 +28,13 @@
> */
> #define IS_ENABLED(option) config_enabled(option, 0)
>
> +/*
> + * IF_ENABLED(CONFIG_FOO, opt_cfg, def_val) evalutes to opt_cfg if
> + * CONFIG_FOO is set to 'y' and to def_val otherwise.
> + */
> +#define IF_ENABLED(option, opt_cfg, def_val) \
> + config_opt_enabled(IS_ENABLED(option), opt_cfg, def_val)
> +
> /*
> * U-Boot add-on: Helper macros to reference to different macros (prefixed by
> * CONFIG_, CONFIG_SPL_, CONFIG_TPL_ or CONFIG_TOOLS_), depending on the
> build
