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Date: Sun, 19 Apr 2020 05:07:43 +0900 From: Masahiro Yamada <masahiroy@...nel.org> To: Nicolas Pitre <nico@...xnic.net> Cc: Saeed Mahameed <saeedm@...lanox.com>, Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>, Jason Gunthorpe <jgg@...pe.ca>, Jani Nikula <jani.nikula@...ux.intel.com>, Neil Armstrong <narmstrong@...libre.com>, Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Leon Romanovsky <leon@...nel.org>, Kieran Bingham <kieran.bingham+renesas@...asonboard.com>, jonas@...boo.se, David Airlie <airlied@...ux.ie>, jernej.skrabec@...l.net, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Networking <netdev@...r.kernel.org>, linux-rdma@...r.kernel.org Subject: Re: [RFC PATCH 1/2] Kconfig: Introduce "uses" keyword On Sun, Apr 19, 2020 at 4:11 AM Nicolas Pitre <nico@...xnic.net> wrote: > > On Sun, 19 Apr 2020, Masahiro Yamada wrote: > > > (FOO || !FOO) is difficult to understand, but > > the behavior of "uses FOO" is as difficult to grasp. > > Can't this be expressed as the following instead: > > depends on FOO if FOO > > That would be a little clearer. > > > Nicolas 'depends on' does not take the 'if <expr>' 'depends on A if B' is the syntax sugar of 'depends on (A || !B), right ? I do not know how clearer it would make things. depends on (m || FOO != m) is another equivalent, but we are always talking about a matter of expression. How important is it to stick to depends on (FOO || !FOO) or its equivalents? If a driver wants to use the feature FOO in most usecases, 'depends on FOO' is sensible. If FOO is just optional, you can get rid of the dependency, and IS_REACHABLE() will do logically correct things. I do not think IS_REACHABLE() is too bad, but if it is confusing, we can add one more option to make it explicit. config DRIVER_X tristate "driver x" config DRIVER_X_USES_FOO bool "use FOO from driver X" depends on DRIVER_X depends on DRIVER_X <= FOO help DRIVER_X works without FOO, but Using FOO will provide better usability. Say Y if you want to make driver X use FOO. Of course, if (IS_ENABLED(CONFIG_DRIVER_X_USES_FOO)) foo_init(); works like if (IS_REACHABLE(CONFIG_FOO)) foo_init(); At lease, it will eliminate a question like "I loaded the module FOO, I swear. But my built-in driver X still would not use FOO, why?" -- Best Regards Masahiro Yamada
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