Hi, On 2022-09-02 10:29, Hans de Goede wrote: > Hi Guenter, Arvid, <snip> > > Actually that should be IS_ENABLED since you suggested that > Arvid should use: > > depends on HWMON || HWMON = n > > In the Kconfig bit there is no need for IS_REACHABLE, > note IS_REACHABLE will work too but I generally prefer > to avoid it because cases which actually need it lead > to weirdness where e.g. both HWMON and TOSHIBA_ACPI are > enabled yet TOSHIBA_ACPI will still not have HWMON > support. > > Arvid, sorry about the "noise" here, let me try to > explain. > > First of all lets explain this bit of magic: > > depends on HWMON || HWMON = n > > What this says is that if HWMON is enabled it must > be able to satisfy dependencies on it in toshiba_acpi.c > (or it may also be fully disabled). > > This magic is necessary to avoid a case where > toshiba_acpi gets build into the kernel, but the > hwmon code is a module. In that case linking errors > (unresolved hwmon symbols) will happen when building > the main vmlinuz kernel image. > > So basically what this does is if HWMON is configured > as a module, it limits the choices for TOSHIBA_ACPI > to either n or m and disallows y. > > I hope that so far I'm making sense... Thanks, this clears up quite a bit of confusion. > > So now to the #ifdef-ery. Since HWMON can be a module > when enabled the #define's from Kconfig will either > contain: > > #define CONFIG_HWMON 1 // when builtin, HWMON=y > > or: > > #define CONFIG_HWMON_MODULE 1 // when a module, HWMON=m > > So you would need to write: > > #if defined CONFIG_HWMON || defined CONFIG_HWMON_MODULE > > as a condition > > #if IS_ENABLED(CONFIG_HWMON) > > is a shorthand (macro) for this. > > ### > > Now back to: > > #if IS_REACHABLE(CONFIG_HWMON) > > This is a special macro for when your Kconfig bit would just be: > > depends on HWMON > > in that case TOSHIBA_ACPI might be set to builtin (y) > while the HWMON core/class code is a module. As mentioned > above that would lead to undefined hwmon symbols when > using "#if IS_ENABLED(CONFIG_HWMON)" as test. IS_REACHABLE > is special in that it will disable (evaluate to false) > in the case where the code being build is builtin and > the dependency is a module. > > But that cannot happen here because your Kconfig bit is: > > depends on HWMON || HWMON = n > > So "#if IS_ENABLED(CONFIG_HWMON)" is sufficient. > > TL;DR: please use "#if IS_ENABLED(CONFIG_HWMON)" to test > if the hwmon code should be build. > > Regards, > > Hans All of this will be useful to know in the future as well I imagine, so thanks again. <snip> Best regards, Arvid Norlander
