[PATCH 02/31] kconfig: Add support for conditional values

[Ilias Apalodimas]

On Mon, 1 Nov 2021 at 03:19, 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
>
> then the following code must be used:
>
>  #ifdef CONFIG_WIBBLE
>  static void handle_wibble(void)
>  {
>         int val = CONFIG_WIBBLE_ADDR;
>
>         ...
>  }
>  #endif
>

The example here might be a bit off and we might need this for int
related values. Was this function handle_wibble() supposed to return
an int or not?  We could shield the linker easier here without adding
macros. Something along the lines of
static void handle_wibble(void)
{
#ifdef CONFIG_WIBBLE
int val = CONFIG_WIBBLE_ADDR;
#endif
}

In that case you don't an extra ifdef to call handle_wibble().
Personally I find this easier to read.

>  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.
>
> Add a CONFIG_IF_ENABLED_INT() version as well.
>
> Signed-off-by: Simon Glass <sjg at chromium.org>
> ---
>
>  include/linux/kconfig.h      | 18 ++++++++++++++++++
>  scripts/config_whitelist.txt |  1 +
>  2 files changed, 19 insertions(+)
>
> diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h
> index a1d1a298426..119c698a158 100644
> --- a/include/linux/kconfig.h
> +++ b/include/linux/kconfig.h
> @@ -59,6 +59,18 @@
>   */
>  #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)
> +
>  /*
>   * Count number of arguments to a variadic macro. Currently only need
>   * it for 1, 2 or 3 arguments.
> @@ -113,5 +125,11 @@
>  #define CONFIG_IS_ENABLED(option, ...)                                 \
>         __concat(__CONFIG_IS_ENABLED_, __count_args(option, ##__VA_ARGS__)) (option, ##__VA_ARGS__)
>
> +/*
> + * Evaluates to 0 if SPL_/TPL_/option is not defined, SPL_/TPL_int_option if it
> + * is defined
> + */
> +#define CONFIG_IF_ENABLED_INT(option, int_option) \
> +       CONFIG_IS_ENABLED(option, (CONFIG_VAL(int_option)), (0))
>
>  #endif /* __LINUX_KCONFIG_H */
> diff --git a/scripts/config_whitelist.txt b/scripts/config_whitelist.txt
> index 022a27288c9..f9d9f4a9cfe 100644
> --- a/scripts/config_whitelist.txt
> +++ b/scripts/config_whitelist.txt
> @@ -609,6 +609,7 @@ CONFIG_ICS307_REFCLK_HZ
>  CONFIG_IDE_PREINIT
>  CONFIG_IDE_RESET
>  CONFIG_IDE_SWAP_IO
> +CONFIG_IF_ENABLED_INT
>  CONFIG_IMA
>  CONFIG_IMX
>  CONFIG_IMX6_PWM_PER_CLK
> --
> 2.33.1.1089.g2158813163f-goog
>

Regards
/Ilias