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Message-ID: <20080128212916.GB3842@uranus.ravnborg.org> Date: Mon, 28 Jan 2008 22:29:16 +0100 From: Sam Ravnborg <sam@...nborg.org> To: Randy Dunlap <randy.dunlap@...cle.com> Cc: linux-kbuild <linux-kbuild@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: kbuild: Preparing for merge window On Thu, Jan 24, 2008 at 02:04:22PM -0800, Randy Dunlap wrote: > On Thu, 24 Jan 2008 22:58:13 +0100 Sam Ravnborg wrote: > > > The following is the list of patches queued up for the merge window at the moment. > > I have during the last week done several modpost changes to make section ismatch > > warnings more reliable and I am happy with the modified modpost code now. > > > Hi Sam, > > Can you add (if not already done) a paragraph to kconfig-language.txt > about the preference of using HAVE_feature in Kconfig files vs. > other spellings of that? I just added this and sent it off for pull. I wanted it included and decided that review comments could be addressed in a follow-up patch. Hopefully it is remotely understandable. Sam >From ef8f5f34572a9adc9478840007d9fc4bcd7b6ad8 Mon Sep 17 00:00:00 2001 From: Sam Ravnborg <sam@...nborg.org> Date: Mon, 28 Jan 2008 21:49:46 +0100 Subject: [PATCH] kconfig: document use of HAVE_* It has been discussed on lkml several times but we need it documented as this is new stuff. Signed-off-by: Sam Ravnborg <sam@...nborg.org> --- Documentation/kbuild/kconfig-language.txt | 36 +++++++++++++++++++++++++++++ 1 files changed, 36 insertions(+), 0 deletions(-) diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt index a43fcc6..649cb87 100644 --- a/Documentation/kbuild/kconfig-language.txt +++ b/Documentation/kbuild/kconfig-language.txt @@ -330,6 +330,42 @@ This is a collection of Kconfig tips, most of which aren't obvious at first glance and most of which have become idioms in several Kconfig files. +Adding common features and make the usage configurable +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +It is a common idiom to implement a feature/functionality that are +relevant for some architectures but not all. +The recommended way to do so is to use a config variable named HAVE_* +that is defined in a common Kconfig file and selected by the relevant +architectures. +An example is the generic IOMAP functionality. + +We would in lib/Kconfig see: + +# Generic IOMAP is used to ... +config HAVE_GENERIC_IOMAP + +config GENERIC_IOMAP + depends on HAVE_GENERIC_IOMAP && FOO + +And in lib/Makefile we would see: +obj-$(CONFIG_GENERIC_IOMAP) += iomap.o + +For each architecture using the generic IOMAP functionality we would see: + +config X86 + select ... + select HAVE_GENERIC_IOMAP + select ... + +Note: we use the existing config option and avoid creating a new +config variable to select HAVE_GENERIC_IOMAP. + +Note: the use of the internal config variable HAVE_GENERIC_IOMAP, it is +introduced to overcome the limitation of select which will force a +config option to 'y' no matter the dependencies. +The dependencies are moved to the symbol GENERIC_IOMAP and we avoid the +situation where select forces a symbol equals to 'y'. + Build as module only ~~~~~~~~~~~~~~~~~~~~ To restrict a component build to module-only, qualify its config symbol -- 1.5.4.rc3.14.g44397 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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