[PATCH 2/6] kconfig: Add support for conditional values

[Masahiro Yamada]

On Fri, May 22, 2020 at 11:02 AM Simon Glass <sjg at chromium.org> wrote:
>
> At present if an optional Kconfig value needs to be used it must be
> bracketed by #ifdef. For example, with this Kconfig setup:
>
> config WIBBLE
>         bool "Support wibbles, the world needs more wibbles"
>
> config WIBBLE_ADDR
>         hex "Address of the wibble"
>         depends on WIBBLE




I am not sure if this is a good idea.


If you want to always use CONFIG_WIBBLE_ADDR,
you can get rid of 'depends on WIBBLE'.




> then the following code must be used:
>
>  #ifdef CONFIG_WIBBLE
>  static void handle_wibble(void)
>  {
>         int val = CONFIG_WIBBLE_ADDR;
>
>         ...
>  }
>  #endif
>
>  static void init_machine()
>  {
>  ...
>  #ifdef CONFIG_WIBBLE
>         handle_wibble();
>  #endif
>  }
>
> Add a new IF_ENABLED_INT() to help with this. So now it is possible to
> write, without #ifdefs:
>
>  static void handle_wibble(void)
>  {
>         int val = IF_ENABLED_INT(CONFIG_WIBBLE, CONFIG_WIBBLE_ADDR);
>
>         ...
>  }
>
>  static void init_machine()
>  {
>  ...
>  if (IS_ENABLED(CONFIG_WIBBLE))
>         handle_wibble();
>  }
>
> The value will be 0 if CONFIG_WIBBLE is not defined, and
> CONFIG_WIBBLE_ADDR if it is. This allows us to reduce the use of #ifdef in
> the code, ensuring that the compiler still checks the code even if it is
> not ultimately used for a particular build.
>
> Signed-off-by: Simon Glass <sjg at chromium.org>
> ---
>
>  include/linux/kconfig.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h
> index 3a2da738c4..86cd266540 100644
> --- a/include/linux/kconfig.h
> +++ b/include/linux/kconfig.h
> @@ -79,6 +79,18 @@
>   */
>  #define CONFIG_VAL(option)  config_val(option)
>
> +/* This use a similar mechanism to config_enabled() above */
> +#define config_opt_enabled(cfg, opt_cfg) _config_opt_enabled(cfg, opt_cfg)
> +#define _config_opt_enabled(cfg_val, opt_value) \
> +       __config_opt_enabled(__ARG_PLACEHOLDER_##cfg_val, opt_value)
> +#define __config_opt_enabled(arg1_or_junk, arg2) \
> +       ___config_opt_enabled(arg1_or_junk arg2, 0)
> +#define ___config_opt_enabled(__ignored, val, ...) val
> +
> +/* Evaluates to 0 if option is not defined, int_option if it is defined */
> +#define IF_ENABLED_INT(option, int_option) \
> +       config_opt_enabled(option, int_option)
> +
>  /*
>   * CONFIG_IS_ENABLED(FOO) evaluates to
>   *  1 if CONFIG_SPL_BUILD is undefined and CONFIG_FOO is set to 'y' or 'm',
> --
> 2.27.0.rc0.183.gde8f92d652-goog
>


-- 
Best Regards
Masahiro Yamada