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kernel-dev: Re-write of "Incorporating Out-of-Tree Modules" section.

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(From yocto-docs rev: 1abc8be7a2862d51165615f49c8c9cfab319564b)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark
2012-12-19 13:47:00 -06:00
committed by Richard Purdie
parent bb715c8eb8
commit 9a5376be50
1 changed files with 114 additions and 1 deletions
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115
documentation/kernel-dev/kernel-dev-common.xml
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@@ -783,7 +783,119 @@ details.
<title>Incorporating Out-of-Tree Modules</title>
<para>
While it is always preferable to work with sources integrated into the Linux
While it is always preferable to work with sources integrated
into the Linux kernel sources, if you need an external kernel
module, the <filename>hello-mod.bb</filename> recipe is available
as a template from which you can create your own out-of-tree
Linux kernel module recipe.
</para>
<para>
This template recipe is located in the
<filename>poky</filename> Git repository of the
Yocto Project <ulink url='&YOCTO_GIT_URL;'>Source Repository</ulink>
at:
<literallayout class="monospaced">
poky/meta-skeleton/recipes-kernel/hello-mod/hello-mod_0.1.bb
</literallayout>
</para>
<para>
To get started, copy this recipe to your layer and give it a
meaningful name (e.g. <filename>mymodule_1.0.bb</filename>).
In the same directory, create a directory named
<filename>files</filename> where you can store any source files,
patches, or other files necessary for building
the module that do not come with the sources.
Finally, update the recipe as appropriate for the module.
Typically you will need to set the following variables:
<itemizedlist>
<listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-DESCRIPTION'><filename>DESCRIPTION</filename></ulink>
</para></listitem>
<listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE'><filename>LICENSE*</filename></ulink>
</para></listitem>
<listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
</para></listitem>
<listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
</para></listitem>
</itemizedlist>
</para>
<para>
Depending on the build system used by the module sources, you might
need to make some adjustments.
For example, a typical module <filename>Makefile</filename> looks
much like the one provided with the <filename>hello-mod</filename>
template:
<literallayout class='monospaced'>
obj-m := hello.o
SRC := $(shell pwd)
all:
$(MAKE) -C $(KERNEL_SRC) M=$(SRC)
modules_install:
$(MAKE) -C $(KERNEL_SRC) M=$(SRC) modules_install
...
</literallayout>
</para>
<para>
The important point to note here is the
<filename>KERNEL_SRC</filename> variable.
The module <filename>bbclass</filename> sets this variable,
as well as the <filename>KERNEL_PATH</filename> variable
to <filename>${STAGING_KERNEL_DIR}</filename> with the
necessary Linux kernel build information to build modules.
If your module <filename>Makefile</filename> uses a different
variable, you might want to override the
<filename>do_compile()</filename> step, or create a patch to
the <filename>Makefile</filename> to work with the more typical
<filename>KERNEL_SRC</filename> or <filename>KERNEL_PATH</filename>
variables.
</para>
<para>
After you have prepared your recipe, you will likely want to
include the module in your images.
To do this, see the documentation for the following variables in
the Yocto Project Reference Manual and set one of them as
appropriate in your machine <filename>config</filename> file:
<itemizedlist>
<listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_ESSENTIAL_EXTRA_RDEPENDS'><filename>MACHINE_ESSENTIAL_EXTRA_RDEPENDS</filename></ulink>
</para></listitem>
<listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS'><filename>MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS</filename></ulink>
</para></listitem>
<listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_EXTRA_RDEPENDS'><filename>MACHINE_EXTRA_RDEPENDS</filename></ulink>
</para></listitem>
<listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_EXTRA_RRECOMMENDS'><filename>MACHINE_EXTRA_RRECOMMENDS</filename></ulink>
</para></listitem>
</itemizedlist>
</para>
<para>
modules are often not required for boot and can be excluded from
certain build configurations.
The following allows for the most flexibility:
<literallayout class='monospaced'>
MACHINE_EXTRA_RRECOMMENDS += "kernel-module-mymodule"
</literallayout>
Where the value is derived by appending the module filename without
the <filename>.ko</filename> extension to the string
"kernel-module-".
</para>
<para>
Because the variable is <filename>RRECOMMENDS</filename> and not
a <filename>RDEPENDS</filename> variable, the build will not fail
if this module is not available to include in the image.
</para>
<para>
Original Text:
<literallayout class='monospaced'>
While it is always preferable to work with sources integrated into the Linux
kernel sources, if you have need of an external kernel module, the hello-mod
recipe is available as a template to create your own out-of-tree Linux kernel
module recipe. It is available in the poky repository at:
@@ -844,6 +956,7 @@ extension to the string "kernel-module-".
As it is an RRECOMMENDS (and not an RDEPENDS) variable, the build will not fail
if this module is not available to include in the image.
</literallayout>
</para>
</section>
</chapter>