1169 lines
50 KiB
XML
1169 lines
50 KiB
XML
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
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[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
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<chapter id='kernel-dev-advanced'>
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<title>Working with Advanced Metadata</title>
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<section id='kernel-dev-advanced-overview'>
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<title>Overview</title>
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<para>
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In addition to supporting configuration fragments and patches, the
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Yocto Project kernel tools also support rich
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<ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink> that you can
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use to define complex policies and Board Support Package (BSP) support.
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The purpose of the Metadata and the tools that manage it, known as
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the kern-tools (<filename>kern-tools-native_git.bb</filename>), is
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to help you manage the complexity of the configuration and sources
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used to support multiple BSPs and Linux kernel types.
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</para>
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</section>
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<section id='using-kernel-metadata-in-a-recipe'>
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<title>Using Kernel Metadata in a Recipe</title>
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<para>
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The kernel sources in the Yocto Project contain kernel Metadata, which
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is located in the <filename>meta</filename> branches of the kernel
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source Git repositories.
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This Metadata defines Board Support Packages (BSPs) that
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correspond to definitions in linux-yocto recipes for the same BSPs.
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A BSP consists of an aggregation of kernel policy and enabled
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hardware-specific features.
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The BSP can be influenced from within the linux-yocto recipe.
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<note>
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Linux kernel source that contains kernel Metadata is said to be
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"linux-yocto style" kernel source.
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A Linux kernel recipe that inherits from the
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<filename>linux-yocto.inc</filename> include file is said to be a
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"linux-yocto style" recipe.
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</note>
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</para>
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<para>
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Every linux-yocto style recipe must define the
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<ulink url='&YOCTO_DOCS_REF_URL;#var-KMACHINE'><filename>KMACHINE</filename></ulink>
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variable.
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This variable is typically set to the same value as the
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<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
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variable, which is used by
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<ulink url='&YOCTO_DOCS_DEV_URL;#bitbake-term'>BitBake</ulink>.
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However, in some cases, the variable might instead refer to the
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underlying platform of the <filename>MACHINE</filename>.
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</para>
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<para>
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Multiple BSPs can reuse the same <filename>KMACHINE</filename>
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name if they are built using the same BSP description.
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The "ep108-zynqmp" and "qemuzynqmp" BSP combination
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in the <filename>meta-xilinx</filename>
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layer is a good example of two BSPs using the same
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<filename>KMACHINE</filename> value (i.e. "zynqmp").
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See the <link linkend='bsp-descriptions'>BSP Descriptions</link> section
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for more information.
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</para>
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<para>
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Every linux-yocto style recipe must also indicate the Linux kernel
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source repository branch used to build the Linux kernel.
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The <ulink url='&YOCTO_DOCS_REF_URL;#var-KBRANCH'><filename>KBRANCH</filename></ulink>
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variable must be set to indicate the branch.
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<note>
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You can use the <filename>KBRANCH</filename> value to define an
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alternate branch typically with a machine override as shown here
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from the <filename>meta-emenlow</filename> layer:
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<literallayout class='monospaced'>
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KBRANCH_emenlow-noemgd = "standard/base"
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</literallayout>
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</note>
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</para>
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<para>
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The linux-yocto style recipes can optionally define the following
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variables:
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<literallayout class='monospaced'>
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KERNEL_FEATURES
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LINUX_KERNEL_TYPE
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</literallayout>
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</para>
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<para>
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<ulink url='&YOCTO_DOCS_REF_URL;#var-LINUX_KERNEL_TYPE'><filename>LINUX_KERNEL_TYPE</filename></ulink>
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defines the kernel type to be
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used in assembling the configuration.
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If you do not specify a <filename>LINUX_KERNEL_TYPE</filename>,
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it defaults to "standard".
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Together with
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<ulink url='&YOCTO_DOCS_REF_URL;#var-KMACHINE'><filename>KMACHINE</filename></ulink>,
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<filename>LINUX_KERNEL_TYPE</filename> defines the search
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arguments used by the kernel tools to find the
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appropriate description within the kernel Metadata with which to
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build out the sources and configuration.
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The linux-yocto recipes define "standard", "tiny", and "preempt-rt"
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kernel types.
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See the "<link linkend='kernel-types'>Kernel Types</link>" section
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for more information on kernel types.
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</para>
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<para>
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During the build, the kern-tools search for the BSP description
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file that most closely matches the <filename>KMACHINE</filename>
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and <filename>LINUX_KERNEL_TYPE</filename> variables passed in from the
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recipe.
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The tools use the first BSP description it finds that match
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both variables.
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If the tools cannot find a match, they issue a warning such as
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the following:
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<literallayout class='monospaced'>
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WARNING: Can't find any BSP hardware or required configuration fragments.
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WARNING: Looked at meta/cfg/broken/emenlow-broken/hdw_frags.txt and
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meta/cfg/broken/emenlow-broken/required_frags.txt in directory:
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meta/cfg/broken/emenlow-broken
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</literallayout>
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In this example, <filename>KMACHINE</filename> was set to "emenlow-broken"
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and <filename>LINUX_KERNEL_TYPE</filename> was set to "broken".
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</para>
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<para>
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The tools first search for the <filename>KMACHINE</filename> and
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then for the <filename>LINUX_KERNEL_TYPE</filename>.
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If the tools cannot find a partial match, they will use the
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sources from the <filename>KBRANCH</filename> and any configuration
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specified in the
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<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>.
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</para>
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<para>
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You can use the
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<ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_FEATURES'><filename>KERNEL_FEATURES</filename></ulink>
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variable
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to include features (configuration fragments, patches, or both) that
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are not already included by the <filename>KMACHINE</filename> and
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<filename>LINUX_KERNEL_TYPE</filename> variable combination.
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For example, to include a feature specified as
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"features/netfilter/netfilter.scc",
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specify:
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<literallayout class='monospaced'>
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KERNEL_FEATURES += "features/netfilter/netfilter.scc"
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</literallayout>
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To include a feature called "cfg/sound.scc" just for the
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<filename>qemux86</filename> machine, specify:
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<literallayout class='monospaced'>
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KERNEL_FEATURES_append_qemux86 = " cfg/sound.scc"
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</literallayout>
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The value of the entries in <filename>KERNEL_FEATURES</filename>
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are dependent on their location within the kernel Metadata itself.
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The examples here are taken from the <filename>meta</filename>
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branch of the <filename>linux-yocto-3.19</filename> repository.
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Within that branch, "features" and "cfg" are subdirectories of the
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<filename>meta/cfg/kernel-cache</filename> directory.
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For more information, see the
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"<link linkend='kernel-metadata-syntax'>Kernel Metadata Syntax</link>" section.
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<note>
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The processing of the these variables has evolved some between the
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0.9 and 1.3 releases of the Yocto Project and associated
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kern-tools sources.
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The descriptions in this section are accurate for 1.3 and later
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releases of the Yocto Project.
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</note>
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</para>
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</section>
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<section id='kernel-metadata-syntax'>
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<title>Kernel Metadata Syntax</title>
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<para>
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The kernel Metadata consists of three primary types of files:
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<filename>scc</filename>
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<footnote>
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<para>
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<filename>scc</filename> stands for Series Configuration
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Control, but the naming has less significance in the
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current implementation of the tooling than it had in the
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past.
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Consider <filename>scc</filename> files to be description files.
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</para>
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</footnote>
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description files, configuration fragments, and patches.
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The <filename>scc</filename> files define variables and include or
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otherwise reference any of the three file types.
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The description files are used to aggregate all types of kernel
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Metadata into
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what ultimately describes the sources and the configuration required
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to build a Linux kernel tailored to a specific machine.
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</para>
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<para>
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The <filename>scc</filename> description files are used to define two
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fundamental types of kernel Metadata:
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<itemizedlist>
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<listitem><para>Features</para></listitem>
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<listitem><para>Board Support Packages (BSPs)</para></listitem>
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</itemizedlist>
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</para>
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<para>
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Features aggregate sources in the form of patches and configuration
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fragments into a modular reusable unit.
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You can use features to implement conceptually separate kernel
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Metadata descriptions such as pure configuration fragments,
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simple patches, complex features, and kernel types.
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<link linkend='kernel-types'>Kernel types</link> define general
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kernel features and policy to be reused in the BSPs.
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</para>
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<para>
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BSPs define hardware-specific features and aggregate them with kernel
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types to form the final description of what will be assembled and built.
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</para>
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<para>
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While the kernel Metadata syntax does not enforce any logical
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separation of configuration fragments, patches, features or kernel
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types, best practices dictate a logical separation of these types
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of Metadata.
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The following Metadata file hierarchy is recommended:
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<literallayout class='monospaced'>
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<replaceable>base</replaceable>/
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bsp/
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cfg/
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features/
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ktypes/
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patches/
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</literallayout>
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</para>
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<para>
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The <filename>bsp</filename> directory contains the
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<link linkend='bsp-descriptions'>BSP descriptions</link>.
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The remaining directories all contain "features".
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Separating <filename>bsp</filename> from the rest of the structure
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aids conceptualizing intended usage.
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</para>
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<para>
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Use these guidelines to help place your <filename>scc</filename>
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description files within the structure:
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<itemizedlist>
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<listitem><para>If your file contains
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only configuration fragments, place the file in the
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<filename>cfg</filename> directory.</para></listitem>
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<listitem><para>If your file contains
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only source-code fixes, place the file in the
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<filename>patches</filename> directory.</para></listitem>
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<listitem><para>If your file encapsulates
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a major feature, often combining sources and configurations,
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place the file in <filename>features</filename> directory.
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</para></listitem>
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<listitem><para>If your file aggregates
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non-hardware configuration and patches in order to define a
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base kernel policy or major kernel type to be reused across
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multiple BSPs, place the file in <filename>ktypes</filename>
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directory.
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</para></listitem>
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</itemizedlist>
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</para>
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<para>
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These distinctions can easily become blurred - especially as
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out-of-tree features slowly merge upstream over time.
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Also, remember that how the description files are placed is
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a purely logical organization and has no impact on the functionality
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of the kernel Metadata.
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There is no impact because all of <filename>cfg</filename>,
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<filename>features</filename>, <filename>patches</filename>, and
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<filename>ktypes</filename>, contain "features" as far as the kernel
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tools are concerned.
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</para>
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<para>
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Paths used in kernel Metadata files are relative to
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<filename><base></filename>, which is either
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<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
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if you are creating Metadata in
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<link linkend='recipe-space-metadata'>recipe-space</link>,
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or <filename>meta/cfg/kernel-cache/</filename> if you are creating
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<link linkend='metadata-outside-the-recipe-space'>Metadata outside of the recipe-space</link>.
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</para>
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<section id='configuration'>
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<title>Configuration</title>
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<para>
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The simplest unit of kernel Metadata is the configuration-only
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feature.
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This feature consists of one or more Linux kernel configuration
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parameters in a configuration fragment file
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(<filename>.cfg</filename>) and a <filename>.scc</filename> file
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that describes the fragment.
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</para>
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<para>
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The Symmetric Multi-Processing (SMP) fragment included in the
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<filename>linux-yocto-3.19</filename> Git repository
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consists of the following two files:
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<literallayout class='monospaced'>
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cfg/smp.scc:
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define KFEATURE_DESCRIPTION "Enable SMP"
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define KFEATURE_COMPATIBILITY all
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kconf hardware smp.cfg
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cfg/smp.cfg:
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CONFIG_SMP=y
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CONFIG_SCHED_SMT=y
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# Increase default NR_CPUS from 8 to 64 so that platform with
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# more than 8 processors can be all activated at boot time
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CONFIG_NR_CPUS=64
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</literallayout>
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You can find information on configuration fragment files in the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#creating-config-fragments'>Creating Configuration Fragments</ulink>"
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section of the Yocto Project Development Manual and in
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the "<link linkend='generating-configuration-files'>Generating Configuration Files</link>"
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section earlier in this manual.
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</para>
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<para>
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<ulink url='&YOCTO_DOCS_REF_URL;#var-KFEATURE_DESCRIPTION'><filename>KFEATURE_DESCRIPTION</filename></ulink>
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provides a short description of the fragment.
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Higher level kernel tools use this description.
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</para>
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<para>
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The <filename>kconf</filename> command is used to include the
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actual configuration fragment in an <filename>.scc</filename>
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file, and the "hardware" keyword identifies the fragment as
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being hardware enabling, as opposed to general policy,
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which would use the "non-hardware" keyword.
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The distinction is made for the benefit of the configuration
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validation tools, which warn you if a hardware fragment
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overrides a policy set by a non-hardware fragment.
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<note>
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The description file can include multiple
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<filename>kconf</filename> statements, one per fragment.
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</note>
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</para>
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<para>
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As described in the
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"<link linkend='generating-configuration-files'>Generating Configuration Files</link>"
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section, you can use the following BitBake command to audit your
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configuration:
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<literallayout class='monospaced'>
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$ bitbake linux-yocto -c kernel_configcheck -f
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</literallayout>
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</para>
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</section>
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<section id='patches'>
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<title>Patches</title>
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<para>
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Patch descriptions are very similar to configuration fragment
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descriptions, which are described in the previous section.
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However, instead of a <filename>.cfg</filename> file, these
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descriptions work with source patches.
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</para>
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<para>
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A typical patch includes a description file and the patch itself:
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<literallayout class='monospaced'>
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patches/mypatch.scc:
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patch mypatch.patch
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patches/mypatch.patch:
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<replaceable>typical-patch</replaceable>
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</literallayout>
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You can create the typical <filename>.patch</filename>
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file using <filename>diff -Nurp</filename> or
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<filename>git format-patch</filename>.
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</para>
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<para>
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The description file can include multiple patch statements,
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one per patch.
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</para>
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</section>
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<section id='features'>
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<title>Features</title>
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<para>
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Features are complex kernel Metadata types that consist
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of configuration fragments (<filename>kconf</filename>), patches
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(<filename>patch</filename>), and possibly other feature
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description files (<filename>include</filename>).
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</para>
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<para>
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Here is an example that shows a feature description file:
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<literallayout class='monospaced'>
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features/myfeature.scc
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define KFEATURE_DESCRIPTION "Enable myfeature"
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patch 0001-myfeature-core.patch
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patch 0002-myfeature-interface.patch
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include cfg/myfeature_dependency.scc
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kconf non-hardware myfeature.cfg
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</literallayout>
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This example shows how the <filename>patch</filename> and
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<filename>kconf</filename> commands are used as well as
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how an additional feature description file is included.
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</para>
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<para>
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Typically, features are less granular than configuration
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fragments and are more likely than configuration fragments
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and patches to be the types of things you want to specify
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in the <filename>KERNEL_FEATURES</filename> variable of the
|
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Linux kernel recipe.
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See the "<link linkend='using-kernel-metadata-in-a-recipe'>Using Kernel Metadata in a Recipe</link>"
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section earlier in the manual.
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</para>
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</section>
|
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|
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<section id='kernel-types'>
|
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<title>Kernel Types</title>
|
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|
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<para>
|
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A kernel type defines a high-level kernel policy by
|
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aggregating non-hardware configuration fragments with
|
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patches you want to use when building a Linux kernels of a
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specific type.
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Syntactically, kernel types are no different than features
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as described in the "<link linkend='features'>Features</link>"
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section.
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The <filename>LINUX_KERNEL_TYPE</filename> variable in the kernel
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|
recipe selects the kernel type.
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See the "<link linkend='using-kernel-metadata-in-a-recipe'>Using Kernel Metadata in a Recipe</link>"
|
|
section for more information.
|
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</para>
|
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|
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<para>
|
|
As an example, the <filename>linux-yocto-3.19</filename>
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tree defines three kernel types: "standard",
|
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"tiny", and "preempt-rt":
|
|
<itemizedlist>
|
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<listitem><para>"standard":
|
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Includes the generic Linux kernel policy of the Yocto
|
|
Project linux-yocto kernel recipes.
|
|
This policy includes, among other things, which file
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systems, networking options, core kernel features, and
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debugging and tracing options are supported.
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</para></listitem>
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<listitem><para>"preempt-rt":
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Applies the <filename>PREEMPT_RT</filename>
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patches and the configuration options required to
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build a real-time Linux kernel.
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This kernel type inherits from the "standard" kernel type.
|
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</para></listitem>
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<listitem><para>"tiny":
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Defines a bare minimum configuration meant to serve as a
|
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base for very small Linux kernels.
|
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The "tiny" kernel type is independent from the "standard"
|
|
configuration.
|
|
Although the "tiny" kernel type does not currently include
|
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any source changes, it might in the future.
|
|
</para></listitem>
|
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</itemizedlist>
|
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</para>
|
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|
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<para>
|
|
The "standard" kernel type is defined by
|
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<filename>standard.scc</filename>:
|
|
<literallayout class='monospaced'>
|
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# Include this kernel type fragment to get the standard features and
|
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# configuration values.
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# Include all standard features
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include standard-nocfg.scc
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|
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kconf non-hardware standard.cfg
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# individual cfg block section
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include cfg/fs/devtmpfs.scc
|
|
include cfg/fs/debugfs.scc
|
|
include cfg/fs/btrfs.scc
|
|
include cfg/fs/ext2.scc
|
|
include cfg/fs/ext3.scc
|
|
include cfg/fs/ext4.scc
|
|
|
|
include cfg/net/ipv6.scc
|
|
include cfg/net/ip_nf.scc
|
|
include cfg/net/ip6_nf.scc
|
|
include cfg/net/bridge.scc
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
As with any <filename>.scc</filename> file, a
|
|
kernel type definition can aggregate other
|
|
<filename>.scc</filename> files with
|
|
<filename>include</filename> commands.
|
|
These definitions can also directly pull in
|
|
configuration fragments and patches with the
|
|
<filename>kconf</filename> and <filename>patch</filename>
|
|
commands, respectively.
|
|
</para>
|
|
|
|
<note>
|
|
It is not strictly necessary to create a kernel type
|
|
<filename>.scc</filename> file.
|
|
The Board Support Package (BSP) file can implicitly define
|
|
the kernel type using a <filename>define
|
|
<ulink url='&YOCTO_DOCS_REF_URL;#var-KTYPE'>KTYPE</ulink> myktype</filename>
|
|
line.
|
|
See the "<link linkend='bsp-descriptions'>BSP Descriptions</link>"
|
|
section for more information.
|
|
</note>
|
|
</section>
|
|
|
|
<section id='bsp-descriptions'>
|
|
<title>BSP Descriptions</title>
|
|
|
|
<para>
|
|
BSP descriptions (i.e. <filename>*.scc</filename> files)
|
|
combine kernel types with hardware-specific features.
|
|
The hardware-specific Metadata is typically defined
|
|
independently in the BSP layer, and then aggregated with each
|
|
supported kernel type.
|
|
<note>
|
|
For BSPs supported by the Yocto Project, the BSP description
|
|
files are located in the <filename>bsp</filename> directory
|
|
of the <filename>yocto-kernel-cache</filename> repository
|
|
organized under the "Yocto Linux Kernel" heading in the
|
|
<ulink url='http://git.yoctoproject.org/cgit/cgit.cgi'>Yocto Project Source Repositories</ulink>.
|
|
</note>
|
|
</para>
|
|
|
|
<para>
|
|
This section provides a BSP description structural overview along
|
|
with aggregation concepts as well as a detailed example using
|
|
a BSP supported by the Yocto Project (i.e. Minnow Board).
|
|
</para>
|
|
|
|
<section id='bsp-description-file-overview'>
|
|
<title>Overview</title>
|
|
|
|
<para>
|
|
For simplicity, consider the following top-level BSP
|
|
description file.
|
|
Top-level BSP descriptions files employ both a structure
|
|
and naming convention for consistency.
|
|
The naming convention for the file is as follows:
|
|
<literallayout class='monospaced'>
|
|
<replaceable>bsp_name</replaceable>-<replaceable>kernel_type</replaceable>.scc
|
|
</literallayout>
|
|
Here are some example top-level BSP filenames for the
|
|
Minnow Board BSP, which is supported by the Yocto Project:
|
|
<literallayout class='monospaced'>
|
|
minnow-standard.scc
|
|
minnow-preempt-rt.scc
|
|
minnow-tiny.scc
|
|
</literallayout>
|
|
Each file uses the BSP name followed by the kernel type.
|
|
</para>
|
|
|
|
<para>
|
|
is simple BSP description file whose name has the
|
|
form
|
|
<replaceable>mybsp</replaceable><filename>-standard</filename>
|
|
and supports the <replaceable>mybsp</replaceable> machine using
|
|
a standard kernel:
|
|
<literallayout class='monospaced'>
|
|
define KMACHINE <replaceable>mybsp</replaceable>
|
|
define KTYPE standard
|
|
define KARCH i386
|
|
|
|
include ktypes/standard
|
|
|
|
include <replaceable>mybsp</replaceable>.scc
|
|
|
|
kconf hardware <replaceable>mybsp</replaceable>-<replaceable>extra</replaceable>.cfg
|
|
</literallayout>
|
|
Every top-level BSP description file should define the
|
|
<ulink url='&YOCTO_DOCS_REF_URL;#var-KMACHINE'><filename>KMACHINE</filename></ulink>,
|
|
<ulink url='&YOCTO_DOCS_REF_URL;#var-KTYPE'><filename>KTYPE</filename></ulink>,
|
|
and <ulink url='&YOCTO_DOCS_REF_URL;#var-KARCH'><filename>KARCH</filename></ulink>
|
|
variables.
|
|
These variables allow the OpenEmbedded build system to identify
|
|
the description as meeting the criteria set by the recipe being
|
|
built.
|
|
This simple example supports the "mybsp" machine for the "standard"
|
|
kernel and the "i386" architecture.
|
|
</para>
|
|
|
|
<para>
|
|
Be aware that a hard link between the
|
|
<filename>KTYPE</filename> variable and a kernel type description
|
|
file does not exist.
|
|
Thus, if you do not have kernel types defined in your kernel
|
|
Metadata, you only need to ensure that the kernel recipe's
|
|
<ulink url='&YOCTO_DOCS_REF_URL;#var-LINUX_KERNEL_TYPE'><filename>LINUX_KERNEL_TYPE</filename></ulink>
|
|
variable and the <filename>KTYPE</filename> variable in the
|
|
BSP description file match.
|
|
<note>
|
|
Future versions of the tooling make the specification of
|
|
<filename>KTYPE</filename> in the BSP optional.
|
|
</note>
|
|
</para>
|
|
|
|
<para>
|
|
To separate your kernel policy from your hardware configuration,
|
|
you include a kernel type (<filename>ktype</filename>), such as
|
|
"standard".
|
|
In the previous example, this is done using the following:
|
|
<literallayout class='monospaced'>
|
|
include ktypes/standard
|
|
</literallayout>
|
|
In the previous example, <filename>ktypes/standard.scc</filename>
|
|
aggregates all the configuration fragments, patches, and
|
|
features that make up your standard kernel policy.
|
|
See the "<link linkend='kernel-types'>Kernel Types</link>" section
|
|
for more information.
|
|
</para>
|
|
|
|
<para>
|
|
To aggregate common configurations and features specific to the
|
|
kernel for <replaceable>mybsp</replaceable>, use the following:
|
|
<literallayout class='monospaced'>
|
|
include <replaceable>mybsp</replaceable>.scc
|
|
</literallayout>
|
|
For information on how to break a complete
|
|
<filename>.config</filename> file into the various
|
|
configuration fragments, see the
|
|
"<link linkend='generating-configuration-files'>Generating Configuration Files</link>"
|
|
section.
|
|
</para>
|
|
|
|
<para>
|
|
Finally, if you have any configurations specific to the
|
|
hardware that are not in a <filename>*.scc</filename> file,
|
|
you can include them as follows:
|
|
<literallayout class='monospaced'>
|
|
kconf hardware <replaceable>mybsp</replaceable>-<replaceable>extra</replaceable>.cfg
|
|
</literallayout>
|
|
</para>
|
|
</section>
|
|
|
|
<section id='bsp-description-file-example-minnow'>
|
|
<title>Example</title>
|
|
|
|
<para>
|
|
Many real-world examples are more complex.
|
|
Like any other <filename>.scc</filename> file, BSP
|
|
descriptions can aggregate features.
|
|
Consider the Minnow BSP definition from the
|
|
<filename>linux-yocto-4.4</filename> in the
|
|
Yocto Project
|
|
<ulink url='&YOCTO_DOCS_DEV_URL;#source-repositories'>Source Repositories</ulink>
|
|
(i.e.
|
|
<filename>yocto-kernel-cache/bsp/minnow</filename>):
|
|
<literallayout class='monospaced'>
|
|
minnow.scc:
|
|
include cfg/x86.scc
|
|
include features/eg20t/eg20t.scc
|
|
include cfg/dmaengine.scc
|
|
include features/power/intel.scc
|
|
include cfg/efi.scc
|
|
include features/usb/ehci-hcd.scc
|
|
include features/usb/ohci-hcd.scc
|
|
include features/usb/usb-gadgets.scc
|
|
include features/usb/touchscreen-composite.scc
|
|
include cfg/timer/hpet.scc
|
|
include features/leds/leds.scc
|
|
include features/spi/spidev.scc
|
|
include features/i2c/i2cdev.scc
|
|
include features/mei/mei-txe.scc
|
|
|
|
# Earlyprintk and port debug requires 8250
|
|
kconf hardware cfg/8250.cfg
|
|
|
|
kconf hardware minnow.cfg
|
|
kconf hardware minnow-dev.cfg
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
The <filename>minnow.scc</filename> description file includes
|
|
a hardware configuration fragment
|
|
(<filename>minnow.cfg</filename>) specific to the Minnow
|
|
BSP as well as several more general configuration
|
|
fragments and features enabling hardware found on the
|
|
machine.
|
|
This <filename>minnow.scc</filename> description file is then
|
|
included in each of the three
|
|
"minnow" description files for the supported kernel types
|
|
(i.e. "standard", "preempt-rt", and "tiny").
|
|
Consider the "minnow" description for the "standard" kernel
|
|
type:
|
|
<literallayout class='monospaced'>
|
|
minnow-standard.scc:
|
|
define KMACHINE minnow
|
|
define KTYPE standard
|
|
define KARCH i386
|
|
|
|
include ktypes/standard
|
|
|
|
include minnow.scc
|
|
|
|
# Extra minnow configs above the minimal defined in minnow.scc
|
|
include cfg/efi-ext.scc
|
|
include features/media/media-all.scc
|
|
include features/sound/snd_hda_intel.scc
|
|
|
|
# The following should really be in standard.scc
|
|
# USB live-image support
|
|
include cfg/usb-mass-storage.scc
|
|
include cfg/boot-live.scc
|
|
|
|
# Basic profiling
|
|
include features/latencytop/latencytop.scc
|
|
include features/profiling/profiling.scc
|
|
|
|
# Requested drivers that don't have an existing scc
|
|
kconf hardware minnow-drivers-extra.cfg
|
|
</literallayout>
|
|
The <filename>include</filename> command midway through the file
|
|
includes the <filename>minnow.scc</filename> description that
|
|
defines all enabled hardware for the BSP that is common to
|
|
all kernel types.
|
|
Using this command significantly reduces duplication.
|
|
</para>
|
|
|
|
<para>
|
|
Now consider the "minnow" description for the "tiny" kernel
|
|
type:
|
|
<literallayout class='monospaced'>
|
|
minnow-tiny.scc:
|
|
define KMACHINE minnow
|
|
define KTYPE tiny
|
|
define KARCH i386
|
|
|
|
include ktypes/tiny
|
|
|
|
include minnow.scc
|
|
</literallayout>
|
|
As you might expect, the "tiny" description includes quite a
|
|
bit less.
|
|
In fact, it includes only the minimal policy defined by the
|
|
"tiny" kernel type and the hardware-specific configuration
|
|
required for booting the machine along with the most basic
|
|
functionality of the system as defined in the base "minnow"
|
|
description file.
|
|
</para>
|
|
|
|
<para>
|
|
Notice again the three critical variables:
|
|
<filename>KMACHINE</filename>, <filename>KTYPE</filename>,
|
|
and <filename>KARCH</filename>.
|
|
Of these variables, only the <filename>KTYPE</filename> has changed.
|
|
It is now set to "tiny".
|
|
</para>
|
|
</section>
|
|
</section>
|
|
</section>
|
|
|
|
<section id='kernel-metadata-location'>
|
|
<title>Kernel Metadata Location</title>
|
|
|
|
<para>
|
|
Kernel Metadata always exists outside of the kernel tree either
|
|
defined in a kernel recipe (recipe-space) or outside of the recipe.
|
|
Where you choose to define the Metadata depends on what you want
|
|
to do and how you intend to work.
|
|
Regardless of where you define the kernel Metadata, the syntax used
|
|
applies equally.
|
|
</para>
|
|
|
|
<para>
|
|
If you are unfamiliar with the Linux kernel and only wish
|
|
to apply a configuration and possibly a couple of patches provided to
|
|
you by others, the recipe-space method is recommended.
|
|
This method is also a good approach if you are working with Linux kernel
|
|
sources you do not control or if you just do not want to maintain a
|
|
Linux kernel Git repository on your own.
|
|
For partial information on how you can define kernel Metadata in
|
|
the recipe-space, see the
|
|
"<link linkend='modifying-an-existing-recipe'>Modifying an Existing Recipe</link>"
|
|
section.
|
|
</para>
|
|
|
|
<para>
|
|
Conversely, if you are actively developing a kernel and are already
|
|
maintaining a Linux kernel Git repository of your own, you might find
|
|
it more convenient to work with kernel Metadata kept outside the
|
|
recipe-space.
|
|
Working with Metadata in this area can make iterative development of
|
|
the Linux kernel more efficient outside of the BitBake environment.
|
|
</para>
|
|
|
|
<section id='recipe-space-metadata'>
|
|
<title>Recipe-Space Metadata</title>
|
|
|
|
<para>
|
|
When stored in recipe-space, the kernel Metadata files reside in a
|
|
directory hierarchy below
|
|
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>.
|
|
For a linux-yocto recipe or for a Linux kernel recipe derived
|
|
by copying and modifying
|
|
<filename>oe-core/meta-skeleton/recipes-kernel/linux/linux-yocto-custom.bb</filename>
|
|
to a recipe in your layer, <filename>FILESEXTRAPATHS</filename>
|
|
is typically set to
|
|
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-THISDIR'><filename>THISDIR</filename></ulink><filename>}/${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>.
|
|
See the "<link linkend='modifying-an-existing-recipe'>Modifying an Existing Recipe</link>"
|
|
section for more information.
|
|
</para>
|
|
|
|
<para>
|
|
Here is an example that shows a trivial tree of kernel Metadata
|
|
stored in recipe-space within a BSP layer:
|
|
<literallayout class='monospaced'>
|
|
meta-<replaceable>my_bsp_layer</replaceable>/
|
|
`-- recipes-kernel
|
|
`-- linux
|
|
`-- linux-yocto
|
|
|-- bsp-standard.scc
|
|
|-- bsp.cfg
|
|
`-- standard.cfg
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
When the Metadata is stored in recipe-space, you must take
|
|
steps to ensure BitBake has the necessary information to decide
|
|
what files to fetch and when they need to be fetched again.
|
|
It is only necessary to specify the <filename>.scc</filename>
|
|
files on the
|
|
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>.
|
|
BitBake parses them and fetches any files referenced in the
|
|
<filename>.scc</filename> files by the <filename>include</filename>,
|
|
<filename>patch</filename>, or <filename>kconf</filename> commands.
|
|
Because of this, it is necessary to bump the recipe
|
|
<ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
|
|
value when changing the content of files not explicitly listed
|
|
in the <filename>SRC_URI</filename>.
|
|
</para>
|
|
|
|
<para>
|
|
If the BSP description is in recipe space, you cannot simply list
|
|
the <filename>*.scc</filename> in the <filename>SRC_URI</filename>
|
|
statement.
|
|
You need to use the following form from your kernel append file:
|
|
<literallayout class='monospaced'>
|
|
SRC_URI_append_<replaceable>myplatform</replaceable> = " \
|
|
file://<replaceable>myplatform</replaceable>;type=kmeta;destsuffix=<replaceable>myplatform</replaceable> \
|
|
"
|
|
</literallayout>
|
|
</para>
|
|
</section>
|
|
|
|
<section id='metadata-outside-the-recipe-space'>
|
|
<title>Metadata Outside the Recipe-Space</title>
|
|
|
|
<para>
|
|
When stored outside of the recipe-space, the kernel Metadata
|
|
files reside in a separate repository.
|
|
The OpenEmbedded build system adds the Metadata to the build as
|
|
a "ktype=meta" repository through the
|
|
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
|
|
variable.
|
|
As an example, consider the following <filename>SRC_URI</filename>
|
|
statement from the <filename>linux-yocto_4.4.bb</filename>
|
|
kernel recipe:
|
|
<literallayout class='monospaced'>
|
|
SRC_URI = "git://git.yoctoproject.org/linux-yocto-4.4.git;name=machine;branch=${KBRANCH}; \
|
|
git://git.yoctoproject.org/yocto-kernel-cache;type=kmeta;name=meta;branch=yocto-4.4;destsuffix=${KMETA}"
|
|
</literallayout>
|
|
<filename>${KMETA}</filename>, in this context, is simply used to
|
|
name the directory into which the Git fetcher places the Metadata.
|
|
This behavior is no different than any multi-repository
|
|
<filename>SRC_URI</filename> statement used in a recipe (e.g.
|
|
see the previous section).
|
|
</para>
|
|
|
|
<para>
|
|
You can keep kernel Metadata in a "kernel-cache", which is a
|
|
directory containing configuration fragments.
|
|
As with any Metadata kept outside the recipe-space, you simply
|
|
need to use the <filename>SRC_URI</filename> statement with the
|
|
"type=kmeta" attribute.
|
|
Doing so makes the kernel Metadata available during the
|
|
configuration phase.
|
|
</para>
|
|
|
|
<!--
|
|
|
|
|
|
<para>
|
|
Following is an example that shows how a trivial tree of Metadata
|
|
is stored in a custom Linux kernel Git repository:
|
|
<literallayout class='monospaced'>
|
|
meta/
|
|
`‐‐ cfg
|
|
`‐‐ kernel-cache
|
|
|‐‐ bsp-standard.scc
|
|
|‐‐ bsp.cfg
|
|
`‐‐ standard.cfg
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
To use a branch different from where the sources reside,
|
|
specify the branch in the <filename>KMETA</filename> variable
|
|
in your Linux kernel recipe.
|
|
Here is an example:
|
|
<literallayout class='monospaced'>
|
|
KMETA = "meta"
|
|
</literallayout>
|
|
To use the same branch as the sources, set
|
|
<filename>KMETA</filename> to an empty string:
|
|
<literallayout class='monospaced'>
|
|
KMETA = ""
|
|
</literallayout>
|
|
If you are working with your own sources and want to create an
|
|
orphan <filename>meta</filename> branch, use these commands
|
|
from within your Linux kernel Git repository:
|
|
<literallayout class='monospaced'>
|
|
$ git checkout ‐‐orphan meta
|
|
$ git rm -rf .
|
|
$ git commit ‐‐allow-empty -m "Create orphan meta branch"
|
|
</literallayout>
|
|
</para>
|
|
-->
|
|
|
|
<para>
|
|
If you modify the Metadata, you must not forget to update the
|
|
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRCREV'><filename>SRCREV</filename></ulink>
|
|
statements in the kernel's recipe.
|
|
In particular, you need to update the
|
|
<filename>SRCREV_meta</filename> variable to match the commit in
|
|
the <filename>KMETA</filename> branch you wish to use.
|
|
Changing the data in these branches and not updating the
|
|
<filename>SRCREV</filename> statements to match will cause the
|
|
build to fetch an older commit.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id='organizing-your-source'>
|
|
<title>Organizing Your Source</title>
|
|
|
|
<para>
|
|
Many recipes based on the <filename>linux-yocto-custom.bb</filename>
|
|
recipe use Linux kernel sources that have only a single
|
|
branch - "master".
|
|
This type of repository structure is fine for linear development
|
|
supporting a single machine and architecture.
|
|
However, if you work with multiple boards and architectures,
|
|
a kernel source repository with multiple branches is more
|
|
efficient.
|
|
For example, suppose you need a series of patches for one board to boot.
|
|
Sometimes, these patches are works-in-progress or fundamentally wrong,
|
|
yet they are still necessary for specific boards.
|
|
In these situations, you most likely do not want to include these
|
|
patches in every kernel you build (i.e. have the patches as part of
|
|
the lone "master" branch).
|
|
It is situations like these that give rise to multiple branches used
|
|
within a Linux kernel sources Git repository.
|
|
</para>
|
|
|
|
<para>
|
|
Repository organization strategies exist that maximize source reuse,
|
|
remove redundancy, and logically order your changes.
|
|
This section presents strategies for the following cases:
|
|
<itemizedlist>
|
|
<listitem><para>Encapsulating patches in a feature description
|
|
and only including the patches in the BSP descriptions of
|
|
the applicable boards.</para></listitem>
|
|
<listitem><para>Creating a machine branch in your
|
|
kernel source repository and applying the patches on that
|
|
branch only.</para></listitem>
|
|
<listitem><para>Creating a feature branch in your
|
|
kernel source repository and merging that branch into your
|
|
BSP when needed.</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
|
|
<para>
|
|
The approach you take is entirely up to you
|
|
and depends on what works best for your development model.
|
|
</para>
|
|
|
|
<section id='encapsulating-patches'>
|
|
<title>Encapsulating Patches</title>
|
|
|
|
<para>
|
|
if you are reusing patches from an external tree and are not
|
|
working on the patches, you might find the encapsulated feature
|
|
to be appropriate.
|
|
Given this scenario, you do not need to create any branches in the
|
|
source repository.
|
|
Rather, you just take the static patches you need and encapsulate
|
|
them within a feature description.
|
|
Once you have the feature description, you simply include that into
|
|
the BSP description as described in the
|
|
"<link linkend='bsp-descriptions'>BSP Descriptions</link>"
|
|
section.
|
|
</para>
|
|
|
|
<para>
|
|
You can find information on how to create patches and BSP
|
|
descriptions in the "<link linkend='patches'>Patches</link>" and
|
|
"<link linkend='bsp-descriptions'>BSP Descriptions</link>"
|
|
sections.
|
|
</para>
|
|
</section>
|
|
|
|
<section id='machine-branches'>
|
|
<title>Machine Branches</title>
|
|
|
|
<para>
|
|
When you have multiple machines and architectures to support,
|
|
or you are actively working on board support, it is more
|
|
efficient to create branches in the repository based on
|
|
individual machines.
|
|
Having machine branches allows common source to remain in the
|
|
"master" branch with any features specific to a machine stored
|
|
in the appropriate machine branch.
|
|
This organization method frees you from continually reintegrating
|
|
your patches into a feature.
|
|
</para>
|
|
|
|
<para>
|
|
Once you have a new branch, you can set up your kernel Metadata
|
|
to use the branch a couple different ways.
|
|
In the recipe, you can specify the new branch as the
|
|
<filename>KBRANCH</filename> to use for the board as
|
|
follows:
|
|
<literallayout class='monospaced'>
|
|
KBRANCH = "mynewbranch"
|
|
</literallayout>
|
|
Another method is to use the <filename>branch</filename> command
|
|
in the BSP description:
|
|
<literallayout class='monospaced'>
|
|
mybsp.scc:
|
|
define KMACHINE mybsp
|
|
define KTYPE standard
|
|
define KARCH i386
|
|
include standard.scc
|
|
|
|
branch mynewbranch
|
|
|
|
include mybsp-hw.scc
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
If you find
|
|
yourself with numerous branches, you might consider using a
|
|
hierarchical branching system similar to what the linux-yocto Linux
|
|
kernel repositories use:
|
|
<literallayout class='monospaced'>
|
|
<replaceable>common</replaceable>/<replaceable>kernel_type</replaceable>/<replaceable>machine</replaceable>
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
If you had two kernel types, "standard" and "small" for
|
|
instance, three machines, and <replaceable>common</replaceable>
|
|
as <filename>mydir</filename>, the branches in your
|
|
Git repository might look like this:
|
|
<literallayout class='monospaced'>
|
|
mydir/base
|
|
mydir/standard/base
|
|
mydir/standard/machine_a
|
|
mydir/standard/machine_b
|
|
mydir/standard/machine_c
|
|
mydir/small/base
|
|
mydir/small/machine_a
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
This organization can help clarify the branch relationships.
|
|
In this case, <filename>mydir/standard/machine_a</filename>
|
|
includes everything in <filename>mydir/base</filename> and
|
|
<filename>mydir/standard/base</filename>.
|
|
The "standard" and "small" branches add sources specific to those
|
|
kernel types that for whatever reason are not appropriate for the
|
|
other branches.
|
|
<note>The "base" branches are an artifact of the way Git manages
|
|
its data internally on the filesystem: Git will not allow you
|
|
to use <filename>mydir/standard</filename> and
|
|
<filename>mydir/standard/machine_a</filename> because it
|
|
would have to create a file and a directory named "standard".
|
|
</note>
|
|
</para>
|
|
</section>
|
|
|
|
<section id='feature-branches'>
|
|
<title>Feature Branches</title>
|
|
|
|
<para>
|
|
When you are actively developing new features, it can be more
|
|
efficient to work with that feature as a branch, rather than
|
|
as a set of patches that have to be regularly updated.
|
|
The Yocto Project Linux kernel tools provide for this with
|
|
the <filename>git merge</filename> command.
|
|
</para>
|
|
|
|
<para>
|
|
To merge a feature branch into a BSP, insert the
|
|
<filename>git merge</filename> command after any
|
|
<filename>branch</filename> commands:
|
|
<literallayout class='monospaced'>
|
|
mybsp.scc:
|
|
define KMACHINE mybsp
|
|
define KTYPE standard
|
|
define KARCH i386
|
|
include standard.scc
|
|
|
|
branch mynewbranch
|
|
git merge myfeature
|
|
|
|
include mybsp-hw.scc
|
|
</literallayout>
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id='scc-reference'>
|
|
<title>SCC Description File Reference</title>
|
|
|
|
<para>
|
|
This section provides a brief reference for the commands you can use
|
|
within an SCC description file (<filename>.scc</filename>):
|
|
<itemizedlist>
|
|
<listitem><para><filename>branch [ref]</filename>:
|
|
Creates a new branch relative to the current branch
|
|
(typically <filename>${KTYPE}</filename>) using
|
|
the currently checked-out branch, or "ref" if specified.
|
|
</para></listitem>
|
|
<listitem><para><filename>define</filename>:
|
|
Defines variables, such as <filename>KMACHINE</filename>,
|
|
<filename>KTYPE</filename>, <filename>KARCH</filename>,
|
|
and <filename>KFEATURE_DESCRIPTION</filename>.</para></listitem>
|
|
<listitem><para><filename>include SCC_FILE</filename>:
|
|
Includes an SCC file in the current file.
|
|
The file is parsed as if you had inserted it inline.
|
|
</para></listitem>
|
|
<listitem><para><filename>kconf [hardware|non-hardware] CFG_FILE</filename>:
|
|
Queues a configuration fragment for merging into the final
|
|
Linux <filename>.config</filename> file.</para></listitem>
|
|
<listitem><para><filename>git merge GIT_BRANCH</filename>:
|
|
Merges the feature branch into the current branch.
|
|
</para></listitem>
|
|
<listitem><para><filename>patch PATCH_FILE</filename>:
|
|
Applies the patch to the current Git branch.</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
</section>
|
|
|
|
</chapter>
|
|
<!--
|
|
vim: expandtab tw=80 ts=4
|
|
-->
|