| Message ID | 20230917192009.254979-1-arnd@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] Documentation: kbuild: explain handling optional dependencies | expand |
On Mon, Sep 18, 2023 at 4:20 AM Arnd Bergmann <arnd@kernel.org> wrote: > > From: Arnd Bergmann <arnd@arndb.de> > > This problem frequently comes up in randconfig testing, with > drivers failing to link because of a dependency on an optional > feature. > > The Kconfig language for this is very confusing, so try to > document it in "Kconfig hints" section. > > Reviewed-by: Javier Martinez Canillas <javierm@redhat.com> > Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com> > Reviewed-by: Nicolas Schier <nicolas@fjasle.eu> > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > --- > v2: fix typos pointed out by Nicolas Schier Applied to linux-kbuild. Thanks.
On Mon 25 Sep 2023 16:06:41 GMT, Masahiro Yamada wrote: > On Mon, Sep 18, 2023 at 4:20 AM Arnd Bergmann <arnd@kernel.org> > wrote: > > > > From: Arnd Bergmann <arnd@arndb.de> > > > > This problem frequently comes up in randconfig testing, with > > drivers failing to link because of a dependency on an optional > > feature. > > > > The Kconfig language for this is very confusing, so try to > > document it in "Kconfig hints" section. > > > > Reviewed-by: Javier Martinez Canillas <javierm@redhat.com> > > Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com> > > Reviewed-by: Nicolas Schier <nicolas@fjasle.eu> > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > > --- > > v2: fix typos pointed out by Nicolas Schier > > > Applied to linux-kbuild. Thanks. Hi Masahiro, this patch seems to got lost, or did you intentionally removed it again? Kind regards, Nicolas
On Thu, Feb 15, 2024 at 9:39 PM Nicolas Schier <nicolas@fjasle.eu> wrote: > > On Mon 25 Sep 2023 16:06:41 GMT, Masahiro Yamada wrote: > > On Mon, Sep 18, 2023 at 4:20 AM Arnd Bergmann <arnd@kernel.org> > > wrote: > > > > > > From: Arnd Bergmann <arnd@arndb.de> > > > > > > This problem frequently comes up in randconfig testing, with > > > drivers failing to link because of a dependency on an optional > > > feature. > > > > > > The Kconfig language for this is very confusing, so try to > > > document it in "Kconfig hints" section. > > > > > > Reviewed-by: Javier Martinez Canillas <javierm@redhat.com> > > > Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com> > > > Reviewed-by: Nicolas Schier <nicolas@fjasle.eu> > > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > > > --- > > > v2: fix typos pointed out by Nicolas Schier > > > > > > Applied to linux-kbuild. Thanks. > > Hi Masahiro, > > this patch seems to got lost, or did you intentionally removed it > again? > > Kind regards, > Nicolas Oh? I can see it in the mainline. commit 28d49e171676afb7df7f47798391364af9abed7f Author: Arnd Bergmann <arnd@arndb.de> AuthorDate: Sun Sep 17 21:19:59 2023 +0200 Commit: Masahiro Yamada <masahiroy@kernel.org> CommitDate: Mon Sep 25 16:01:05 2023 +0900 Documentation: kbuild: explain handling optional dependencies
On Thu 15 Feb 2024 22:40:46 GMT, Masahiro Yamada wrote: > On Thu, Feb 15, 2024 at 9:39 PM Nicolas Schier <nicolas@fjasle.eu> > wrote: > > > > On Mon 25 Sep 2023 16:06:41 GMT, Masahiro Yamada wrote: > > > On Mon, Sep 18, 2023 at 4:20 AM Arnd Bergmann <arnd@kernel.org> > > > wrote: > > > > > > > > From: Arnd Bergmann <arnd@arndb.de> > > > > > > > > This problem frequently comes up in randconfig testing, with > > > > drivers failing to link because of a dependency on an optional > > > > feature. > > > > > > > > The Kconfig language for this is very confusing, so try to > > > > document it in "Kconfig hints" section. > > > > > > > > Reviewed-by: Javier Martinez Canillas <javierm@redhat.com> > > > > Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com> > > > > Reviewed-by: Nicolas Schier <nicolas@fjasle.eu> > > > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > > > > --- > > > > v2: fix typos pointed out by Nicolas Schier > > > > > > > > > Applied to linux-kbuild. Thanks. > > > > Hi Masahiro, > > > > this patch seems to got lost, or did you intentionally removed it > > again? > > > > Kind regards, > > Nicolas > > > > Oh? > > I can see it in the mainline. ups, I'm sorry for the noise. You are right, I had an heavily out-dated tree at hand and wasn't aware of it ... Kind regards, Nicolas
diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst index 858ed5d80defe..0135905c0aa35 100644 --- a/Documentation/kbuild/kconfig-language.rst +++ b/Documentation/kbuild/kconfig-language.rst @@ -573,6 +573,32 @@ above, leading to: bool "Support for foo hardware" depends on ARCH_FOO_VENDOR || COMPILE_TEST +Optional dependencies +~~~~~~~~~~~~~~~~~~~~~ + +Some drivers are able to optionally use a feature from another module +or build cleanly with that module disabled, but cause a link failure +when trying to use that loadable module from a built-in driver. + +The most common way to express this optional dependency in Kconfig logic +uses the slightly counterintuitive:: + + config FOO + tristate "Support for foo hardware" + depends on BAR || !BAR + +This means that there is either a dependency on BAR that disallows +the combination of FOO=y with BAR=m, or BAR is completely disabled. +For a more formalized approach if there are multiple drivers that have +the same dependency, a helper symbol can be used, like:: + + config FOO + tristate "Support for foo hardware" + depends on BAR_OPTIONAL + + config BAR_OPTIONAL + def_tristate BAR || !BAR + Kconfig recursive dependency limitations ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~