On Fri, Apr 17, 2020 at 10:12 AM Saeed Mahameed <saeedm@xxxxxxxxxxxx> wrote: > > Due to the changes to the semantics of imply keyword [1], which now > doesn't force any config options to the implied configs any more. > > A module (FOO) that has a weak dependency on some other modules (BAR) > is now broken if it was using imply to force dependency restrictions. > e.g.: FOO needs BAR to be reachable, especially when FOO=y and BAR=m. > Which might now introduce build/link errors. > > There are two options to solve this: > 1. use IS_REACHABLE(BAR), everywhere BAR is referenced inside FOO. > 2. in FOO's Kconfig add: depends on (BAR || !BAR) > > The first option is not desirable, and will leave the user confused when > setting FOO=y and BAR=m, FOO will never reach BAR even though both are > compiled. > > The 2nd one is the preferred approach, and will guarantee BAR is always > reachable by FOO if both are compiled. But, (BAR || !BAR) is really > confusing for those who don't really get how kconfig tristate arithmetics > work. > > To solve this and hide this weird expression and to avoid repetition > across the tree, we introduce new keyword "uses" to the Kconfig options > family. > > uses BAR: > Equivalent to: depends on symbol || !symbol > Semantically it means, if FOO is enabled (y/m) and has the option: > uses BAR, make sure it can reach/use BAR when possible. > > For example: if FOO=y and BAR=m, FOO will be forced to m. > > [1] https://lore.kernel.org/linux-doc/20200302062340.21453-1-masahiroy@xxxxxxxxxx/ > > Link: https://lkml.org/lkml/2020/4/8/839 > Signed-off-by: Saeed Mahameed <saeedm@xxxxxxxxxxxx> > Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx> > Cc: linux-kbuild@xxxxxxxxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx > --- I am not convinced with this patch. This patch adds another way to do the same thing. It is true that it _hides_ the problems, and makes the _surface_ cleaner at best, but the internal will be more complicated. (FOO || !FOO) is difficult to understand, but the behavior of "uses FOO" is as difficult to grasp. People would wonder, "what 'uses FOO' means?", then they would find the explanation in kconfig-language.rst: "Equivalent to: depends on symbol || !symbol Semantically it means, if FOO is enabled (y/m) and has the option: uses BAR, make sure it can reach/use BAR when possible." To understand this correctly, people must study the arithmetic of (symbol || !symbol) anyway. I do not want to extend Kconfig for the iffy syntax sugar. (symbol || !symbol) is horrible. But, I am also scared to see people would think 'uses symbol' is the right thing to do, and start using it liberally all over the place. -- Best Regards Masahiro Yamada
