Re: [PATCH v3 2/3] kconfig: new macro IF_ENABLED()

Hi Heinrich,

On Mon, 20 Feb 2023 at 10:15, Andre Przywara andre.przywara@arm.com wrote:

On Sun, 19 Feb 2023 12:36:28 +0100 Heinrich Schuchardt heinrich.schuchardt@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.schuchardt@canonical.com

Reviewed-by: Andre Przywara andre.przywara@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

This looks good to me, but what should we do with the existing IF_ENABLED_INT()? Perhaps we should drop that in favour of this one, or do we need both?

Regards, Simon