documentation/kernel-manual/kernel-how-to.xml: Partial - Re-write of BSP creation
This is a partial edit of re-writing the BSP creation section so that it is clearer for the naive user. It is not quite done yet. (From yocto-docs rev: 7a552e72a1d2d1b6ffa93f4fe3074f318ff35715) Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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Scott Rifenbark
Richard Purdie
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@ -1021,62 +1021,76 @@ That's it. Configure and build.
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</para>
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<para>
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You can start with something in <filename>meta/conf/machine</filename> - <filename>
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meta/conf/machine/atom-pc.conf</filename> for example. Or, you can start with a machine
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configuration from any of the BSP layers in the meta-intel repository at
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<ulink url='http://git.yoctoproject.org/cgit/cgit.cgi/meta-intel/'></ulink>, such as
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<filename>meta-intel/meta-emenlow/conf/machine/emenlow.conf</filename>.
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You can start with a machine configuration file in the Yocto Project source tree
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such as the <filename>atom-pc.conf</filename> in <filename>meta-yocto/conf/machine</filename>.
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Or, you can start with a machine configuration file from a BSP layer
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such as <filename>emenlow.conf</filename> in <filename>meta-emenlow/conf/machine</filename>.
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</para>
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<para>
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The main difference between the two is that "emenlow" is in its own layer.
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It is in its own layer because it needs extra machine-specific packages such as its
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own video driver and other supporting packages.
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The "atom-pc" is simpler and does not need any special packages - everything it needs can
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be specified in the configuration file.
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The main difference between these two BSP machine configuration files is that "emenlow" is
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in its own isolated BSP layer, while "atom-pc" is in a more encompassing layer
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named <filename>meta-yocto</filename> that is part of the Yocto Project source tree.
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The "emenlow" configuration is in its own BSP layer because the target hardware
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needs extra machine-specific packages to support graphics and other features.
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The "atom-pc" configuration file supports more basic hardware that does not need any
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special packages - everything the hardware needs can be specified in the configuration file.
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The "atom-pc" machine also supports all of Asus eee901, Acer Aspire One, Toshiba NB305,
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and the Intel® Embedded Development Board 1-N450 with no changes.
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</para>
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<para>
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If you want to make minor changes to support a slightly different machine, you can
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create a new configuration file for it and add it alongside the others.
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You might consider keeping the common information separate and including it.
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create a new configuration file for the new machine and add it alongside the
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configuration files.
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You might consider keeping common configurations for several machines in a separate file
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and then including the other configuration files that have more specific configurations.
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</para>
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<para>
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Similarly, you can also use multiple configuration files for different machines even
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if you do it as a separate layer like meta-emenlow.
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when the configuration files come from a separate and different layer.
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</para>
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<para>
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As an example consider this:
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<itemizedlist>
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<listitem><para>Copy meta-emenlow to meta-mymachine</para></listitem>
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<listitem><para>Fix or remove anything you do not need.
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For this example the only thing left was the kernel directory with a
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<filename>linux-yocto_git.bbappend</filename>
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file
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and <filename>meta-mymachine/conf/machine/mymachine.conf</filename>
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(linux-yocto is the kernel listed in
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<filename>meta-emenlow/conf/machine/emenlow.conf</filename>)</para></listitem>.
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<listitem><para>Add a new entry in the <filename>build/conf/bblayers.conf</filename>
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so the new layer can be found by BitBake.</para></listitem>
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</itemizedlist>
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<orderedlist>
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<listitem><para>Copy the "emenlow" BSP layer to a new BSP layer named
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<filename>meta-mymachine</filename>.
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Now you have two identical BSP layers ‐ but with different names.</para></listitem>
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<listitem><para>This example assumes you only need to change some machine
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configurations and inform the Yocto Project build process of the new layer.
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Consequently, modify the new layer's structure so that all it contains
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is the <filename>linux-yocto_git.bbappend</filename> file in the
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<filename>meta-mymachine/recipes-kernel/linux</filename> directory
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and the <filename>emenlow.conf</filename> configuration file in the
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<filename>meta-mymachine/conf/machine</filename> directory.
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Note that "linux-yocto" is the kernel specified in the <filename>mymachine.conf</filename>
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configuration file.</para></listitem>.
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<listitem><para>Rename the <filename>emenlow.conf</filename> file to <filename>mymachine.conf</filename>
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and fix or remove any configurations.</para></listitem>
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<listitem><para>Make sure the Yocto Project build process knows about the new BSP
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layer by adding the layer to the <filename>bblayers.conf</filename> configuration
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file located in the Yocto Project build tree at <filename>build/conf/bblayers.conf</filename>.
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Adding the layer allows Bitbake to find the new layer.
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You also need to edit the <filename>layer.conf</filename> file located in the
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<filename>meta-mymachine/conf</filename> directory such that "mymachine" replaces
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"emenlow".</para></listitem>
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</orderedlist>
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</para></listitem>
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<listitem><para>
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Create a machine branch for your machine.
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Create a machine branch for your machine in a the Yocto Project git repository.
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</para>
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<para>
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For the kernel to compile successfully, you need to create a branch in the git repository
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specifically named for your machine.
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To create this branch first create a bare clone of the Yocto Project git repository.
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Next, create a local clone of that:
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For the kernel to compile successfully, you need to create a branch in the
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Yocto Project git repository that is specifically named for your machine.
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To create this branch, first create a bare clone of the Yocto Project git repository.
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Then, create a local clone of that bare clone.
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Here are the commands:
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<literallayout class='monospaced'>
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$ git clone --bare git://git.yoctoproject.org/linux-yocto-2.6.37.git
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linux-yocto-2.6.37.git
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$ git clone --bare git://git.yoctoproject.org/linux-yocto-2.6.37.git linux-yocto-2.6.37.git
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$ git clone linux-yocto-2.6.37.git linux-yocto-2.6.37
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</literallayout>
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</para>
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@ -1090,8 +1104,12 @@ That's it. Configure and build.
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</para></listitem>
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<listitem><para>
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In a layer, create a <filename>linux-yocto_git.bbappend</filename>
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file with the following:
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In your new layer you need to edit the <filename>linux-yocto_git.bbappend</filename>
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file so that the compatible machine is "mymachine".
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It is also convenient point to a cloned Yocto Project git repository that is local
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to your system for development purposes.
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Thus, change the <filename>linux-yocto_git.bbappend</filename> file in your
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<filename>meta-mymachine</filename> layer to the following:
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</para>
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<para>
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@ -1099,11 +1117,11 @@ That's it. Configure and build.
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FILESEXTRAPATHS := "${THISDIR}/${PN}"
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COMPATIBLE_MACHINE_mymachine = "mymachine"
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# It is often nice to have a local clone of the kernel repository, to
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# It is often nice to have a clone of the kernel repository, to
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# allow patches to be staged, branches created, and so forth. Modify
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# KSRC to point to your local clone as appropriate.
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# KSRC to point to your bare clone as appropriate.
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KSRC ?= /path/to/your/bare/clone/for/example/linux-yocto-2.6.37.git
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KSRC ?= $MYWORK/linux-yocto-2.6.37.git
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# KMACHINE is the branch to be built, or alternatively
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# KBRANCH can be directly set.
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@ -1117,7 +1135,9 @@ That's it. Configure and build.
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</para>
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<para>
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After doing that, select the machine in <filename>build/conf/local.conf</filename>:
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After updating the <filename>linux-yocto_git.bbappend</filename> file,
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edit the <filename>build/conf/local.conf</filename> found
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in the Yocto Project build tree so that it selects your machine:
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<literallayout class='monospaced'>
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#
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MACHINE ?= "mymachine"
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@ -1137,7 +1157,7 @@ That's it. Configure and build.
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</para>
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<para>
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Of course, that will give you a kernel with the default configuration file, which is probably
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At this point you will build a kernel with the default configuration file, which is probably
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not what you want.
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If you just want to set some kernel configuration options, you can do that by
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putting them in a file.
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@ -1155,7 +1175,7 @@ That's it. Configure and build.
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</literallayout>
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<para>
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These config fragments could then be picked up and
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These configuration fragments could then be picked up and
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applied to the kernel .config by appending them to the kernel SRC_URI:
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</para>
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