documentation/bsp-guide/bsp.xml: Updated the Linux Kernel Configuration section
These changes are another round of edits from Tom Z. Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
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Scott Rifenbark
Richard Purdie
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885dbc7364
commit
6224858276
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@ -324,21 +324,22 @@ meta-<bsp_name>/recipes-kernel/linux/linux-wrs_git.bbappend
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<para>
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For your BSP you typically want to use an existing Poky kernel found in the
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Poky repository at <filename class='directory'>meta/recipes-kernel/kernel</filename>.
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You can append your specific changes to the kernel by using a
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<filename>.bbappend</filename> file, which is located in the
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<filename class='directory'>meta-<bsp_name>/recipes-kernel/linux</filename>
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You can append your specific changes to the kernel recipe by using an append file,
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which is located in the
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<filename class='directory'>meta-<bsp_name>/recipes-kernel/linux</filename>
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directory.
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</para>
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<para>
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Consider a BSP that uses the <filename>linux-yocto-stable_git.bb</filename> kernel.
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You would use the <filename>linux-yocto-stable_git.bbappend</filename> file to add
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Consider a BSP that uses the <filename>linux-yocto-stable_git.bb</filename> kernel,
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which is the preferred kernel to use for developing a new BSP using the Yocto Project.
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You would use the <filename>linux-yocto-stable_git.bbappend</filename> file to append
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specific BSP settings to the kernel, thus configuring the kernel for your particular BSP.
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</para>
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<para>
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Consider an example for the existing "crownbay" BSP.
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The <filename>.bbaappend</filename> file used for the "crownbay" BSP is:
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The append file used for the "crownbay" BSP is:
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<programlisting>
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meta-crownbay/recipes-kernel/linux/linux-wrs_git.bbappend
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meta-crownbay/recipes-kernel/linux/linux-yocto-stable_git.bbappend
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</programlisting>
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The file contains the following:
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<programlisting>
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@ -346,31 +347,67 @@ FILESEXTRAPATHS := "${THISDIR}/${PN}"
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COMPATIBLE_MACHINE_crownbay = "cronwbay"
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KMACHINE_crownbay = "crownbay"
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</programlisting>
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This <filename>.bbappend</filename> file adds "crownbay" as a compatible machine,
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This append file adds "crownbay" as a compatible machine,
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and additionally sets a Yocto Kernel-specific variable that identifies the name of the
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BSP branch to use in the GIT repository to find configuration information.
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</para>
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<note><para>
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For an established BSP the configuration information is incorporated directly into the
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git tree.
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For a new BSP, however, the <filename>.bbappend</filename> file needs to
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include its own set of configuration options in a file called
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<filename>defconfig</filename> located in a directory that matches the recipe name.
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<para>
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One thing missing in this particular BSP, which you will typically need when
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developing a BSP, is the kernel configuration (.config) for your BSP.
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When developing a BSP, you probably have a kernel configuration file or a set of kernel
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configuration files that, when taken together, define the kernel configuration for your BSP.
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You can accomplish this definition by putting the configurations in a file or a set of files
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inside a directory located at the same level as your append file and having the same name
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as the kernel.
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With all these conditions met simply reference those files in a SRC_URI statement in the append
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file.
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</para>
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<para>
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For example, suppose you had a set of configuration options in a file called
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<filename>defonfig</filename>.
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If you put that file inside a directory named
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<filename class='directory'>/linux-yocto-stable_git</filename> and then added
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a SRC_URI statement such as the following to the append file, those configuration
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options will be picked up and applied when the kernel is built.
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<programlisting>
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SRC_URI += "file://defconfig"
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</programlisting>
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Once a BSP is committed, the Yocto kernel maintainer moves this configuration information
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into the git tree so that the <filename>.bbappend</filename> file does not need to locate
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its own configuration options.
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Again, the initial configuration options using the SRC_URI are put into a
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directory named
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<filename class='directory'>meta-<bsp_name>/recipes/linux/linux-yocto-stable</filename>.
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</para>
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<para>
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You can find more information about creating a BSP that is based on an existing similar
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BSP by reading the "Creating a BSP Based on an Existing Similar BSP" section in the
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"<ulink url="http://www.yoctoproject.org/community/documentation">Yocto Project
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Kernel Architecture and Use Manual</ulink>".
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As mentioned earlier, you can group related configurations into multiple files and
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name them all in the SRC_URI statement as well.
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For example, you could group separate configurations specifically for ethernet and graphics
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into their own files and add those by using a SRC_URI statement like the
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following in your append file:
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<programlisting>
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SRC_URI += "file://defconfig \
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file://eth.cfg \
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file://gfx.cfg"
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</programlisting>
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</para>
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<para>
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The FILESEXTRAPATHS variable is boilerplated here in order to make it easy to do that.
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It basically allows those configuration files to be found by the build process.
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</para>
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<note><para>
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Other methods exist to accomplish grouping and defining configuration options.
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For example, you could directly add configuration options to the Yocto kernel
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<filename class='directory'>wrs_meta</filename> branch for your BSP.
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The configuration options will likely end up in that location anyway if the BSP gets
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added to the Yocto Project.
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For information on how to add these configurations directly, see the
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"Yocto Project Kernel Architecture and Use Manual" on the
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<ulink url="http://yoctoproject.org/community/documentation">Yocto Project website
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Documentation Page</ulink>
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</para>
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<para>
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In general, however, the Yocto Project maintainers take care of moving the SRC_URI-specified
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configuration options to the <filename class='directory'>wrs_meta</filename> branch.
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Not only is it easier for BSP developers to not have to worry about putting those
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configurations in the branch, but having the manintainers do it allows them to apply
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'global' knowledge about the kinds of common configuration options multiple BSPs in
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the tree are typically using.
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This allows for promotion of common configurations into common features.
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</para></note>
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</section>
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