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

[Heinrich Schuchardt]

On 5/22/20 4:17 AM, Masahiro Yamada wrote:
> 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'.
>
>

Hello Simon,

what is the effect on the code size if you eliminate the #ifdefs?

Isn't this move growing the size of the U-Boot binary?

Best regards

Heinrich

>
>
>> 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
>>
>
>