Revert "poky: subtree update:b23aa6b753..ad30a6d470"
This reverts commit af5e4ef732faedf66c6dc1756432e9de2ac72988.
This commit introduced openbmc/openbmc#3720 and no solution has been
forthcoming. Revert until we can get to the bottom of this.
Change-Id: I2fb0d81eb26cf3dadb2f2abdd1a1bb7a95eaf03c
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+<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
+[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
+<!--SPDX-License-Identifier: CC-BY-2.0-UK-->
+
+<chapter id='kernel-dev-advanced'>
+<title>Working with Advanced Metadata (<filename>yocto-kernel-cache</filename>)</title>
+
+<section id='kernel-dev-advanced-overview'>
+ <title>Overview</title>
+
+ <para>
+ In addition to supporting configuration fragments and patches, the
+ Yocto Project kernel tools also support rich
+ <ulink url='&YOCTO_DOCS_REF_URL;#metadata'>Metadata</ulink> that you can
+ use to define complex policies and Board Support Package (BSP) support.
+ The purpose of the Metadata and the tools that manage it is
+ to help you manage the complexity of the configuration and sources
+ used to support multiple BSPs and Linux kernel types.
+ </para>
+
+ <para>
+ Kernel Metadata exists in many places.
+ One area in the Yocto Project
+ <ulink url='&YOCTO_DOCS_OM_URL;#source-repositories'>Source Repositories</ulink>
+ is the <filename>yocto-kernel-cache</filename> Git repository.
+ You can find this repository grouped under the "Yocto Linux Kernel"
+ heading in the
+ <ulink url='&YOCTO_GIT_URL;'>Yocto Project Source Repositories</ulink>.
+ </para>
+
+ <para>
+ Kernel development tools ("kern-tools") exist also in the Yocto
+ Project Source Repositories under the "Yocto Linux Kernel" heading
+ in the <filename>yocto-kernel-tools</filename> Git repository.
+ The recipe that builds these tools is
+ <filename>meta/recipes-kernel/kern-tools/kern-tools-native_git.bb</filename>
+ in the
+ <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
+ (e.g. <filename>poky</filename>).
+ </para>
+</section>
+
+<section id='using-kernel-metadata-in-a-recipe'>
+ <title>Using Kernel Metadata in a Recipe</title>
+
+ <para>
+ As mentioned in the introduction, the Yocto Project contains kernel
+ Metadata, which is located in the
+ <filename>yocto-kernel-cache</filename> Git repository.
+ This Metadata defines Board Support Packages (BSPs) that
+ correspond to definitions in linux-yocto recipes for corresponding BSPs.
+ A BSP consists of an aggregation of kernel policy and enabled
+ hardware-specific features.
+ The BSP can be influenced from within the linux-yocto recipe.
+ <note>
+ A Linux kernel recipe that contains kernel Metadata (e.g.
+ inherits from the <filename>linux-yocto.inc</filename> file)
+ is said to be a "linux-yocto style" recipe.
+ </note>
+ </para>
+
+ <para>
+ Every linux-yocto style recipe must define the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-KMACHINE'><filename>KMACHINE</filename></ulink>
+ variable.
+ This variable is typically set to the same value as the
+ <filename>MACHINE</filename> variable, which is used by
+ <ulink url='&YOCTO_DOCS_REF_URL;#bitbake-term'>BitBake</ulink>.
+ However, in some cases, the variable might instead refer to the
+ underlying platform of the <filename>MACHINE</filename>.
+ </para>
+
+ <para>
+ Multiple BSPs can reuse the same <filename>KMACHINE</filename>
+ name if they are built using the same BSP description.
+ Multiple Corei7-based BSPs could share the same "intel-corei7-64"
+ value for <filename>KMACHINE</filename>.
+ It is important to realize that <filename>KMACHINE</filename> is
+ just for kernel mapping, while <filename>MACHINE</filename>
+ is the machine type within a BSP Layer.
+ Even with this distinction, however, these two variables can hold
+ the same value.
+ See the <link linkend='bsp-descriptions'>BSP Descriptions</link>
+ section for more information.
+ </para>
+
+ <para>
+ Every linux-yocto style recipe must also indicate the Linux kernel
+ source repository branch used to build the Linux kernel.
+ The <ulink url='&YOCTO_DOCS_REF_URL;#var-KBRANCH'><filename>KBRANCH</filename></ulink>
+ variable must be set to indicate the branch.
+ <note>
+ You can use the <filename>KBRANCH</filename> value to define an
+ alternate branch typically with a machine override as shown here
+ from the <filename>meta-yocto-bsp</filename> layer:
+ <literallayout class='monospaced'>
+ KBRANCH_edgerouter = "standard/edgerouter"
+ </literallayout>
+ </note>
+ </para>
+
+ <para>
+ The linux-yocto style recipes can optionally define the following
+ variables:
+ <literallayout class='monospaced'>
+ KERNEL_FEATURES
+ LINUX_KERNEL_TYPE
+ </literallayout>
+ </para>
+
+ <para>
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-LINUX_KERNEL_TYPE'><filename>LINUX_KERNEL_TYPE</filename></ulink>
+ defines the kernel type to be
+ used in assembling the configuration.
+ If you do not specify a <filename>LINUX_KERNEL_TYPE</filename>,
+ it defaults to "standard".
+ Together with <filename>KMACHINE</filename>,
+ <filename>LINUX_KERNEL_TYPE</filename> defines the search
+ arguments used by the kernel tools to find the
+ appropriate description within the kernel Metadata with which to
+ build out the sources and configuration.
+ The linux-yocto recipes define "standard", "tiny", and "preempt-rt"
+ kernel types.
+ See the "<link linkend='kernel-types'>Kernel Types</link>" section
+ for more information on kernel types.
+ </para>
+
+ <para>
+ During the build, the kern-tools search for the BSP description
+ file that most closely matches the <filename>KMACHINE</filename>
+ and <filename>LINUX_KERNEL_TYPE</filename> variables passed in from the
+ recipe.
+ The tools use the first BSP description it finds that match
+ both variables.
+ If the tools cannot find a match, they issue a warning.
+ </para>
+
+ <para>
+ The tools first search for the <filename>KMACHINE</filename> and
+ then for the <filename>LINUX_KERNEL_TYPE</filename>.
+ If the tools cannot find a partial match, they will use the
+ sources from the <filename>KBRANCH</filename> and any configuration
+ specified in the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>.
+ </para>
+
+ <para>
+ You can use the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_FEATURES'><filename>KERNEL_FEATURES</filename></ulink>
+ variable
+ to include features (configuration fragments, patches, or both) that
+ are not already included by the <filename>KMACHINE</filename> and
+ <filename>LINUX_KERNEL_TYPE</filename> variable combination.
+ For example, to include a feature specified as
+ "features/netfilter/netfilter.scc",
+ specify:
+ <literallayout class='monospaced'>
+ KERNEL_FEATURES += "features/netfilter/netfilter.scc"
+ </literallayout>
+ To include a feature called "cfg/sound.scc" just for the
+ <filename>qemux86</filename> machine, specify:
+ <literallayout class='monospaced'>
+ KERNEL_FEATURES_append_qemux86 = " cfg/sound.scc"
+ </literallayout>
+ The value of the entries in <filename>KERNEL_FEATURES</filename>
+ are dependent on their location within the kernel Metadata itself.
+ The examples here are taken from the
+ <filename>yocto-kernel-cache</filename> repository.
+ Each branch of this repository contains "features" and "cfg"
+ subdirectories at the top-level.
+ For more information, see the
+ "<link linkend='kernel-metadata-syntax'>Kernel Metadata Syntax</link>"
+ section.
+ </para>
+</section>
+
+<section id='kernel-metadata-syntax'>
+ <title>Kernel Metadata Syntax</title>
+
+ <para>
+ The kernel Metadata consists of three primary types of files:
+ <filename>scc</filename>
+ <footnote>
+ <para>
+ <filename>scc</filename> stands for Series Configuration
+ Control, but the naming has less significance in the
+ current implementation of the tooling than it had in the
+ past.
+ Consider <filename>scc</filename> files to be description files.
+ </para>
+ </footnote>
+ description files, configuration fragments, and patches.
+ The <filename>scc</filename> files define variables and include or
+ otherwise reference any of the three file types.
+ The description files are used to aggregate all types of kernel
+ Metadata into
+ what ultimately describes the sources and the configuration required
+ to build a Linux kernel tailored to a specific machine.
+ </para>
+
+ <para>
+ The <filename>scc</filename> description files are used to define two
+ fundamental types of kernel Metadata:
+ <itemizedlist>
+ <listitem><para>Features</para></listitem>
+ <listitem><para>Board Support Packages (BSPs)</para></listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ Features aggregate sources in the form of patches and configuration
+ fragments into a modular reusable unit.
+ You can use features to implement conceptually separate kernel
+ Metadata descriptions such as pure configuration fragments,
+ simple patches, complex features, and kernel types.
+ <link linkend='kernel-types'>Kernel types</link> define general
+ kernel features and policy to be reused in the BSPs.
+ </para>
+
+ <para>
+ BSPs define hardware-specific features and aggregate them with kernel
+ types to form the final description of what will be assembled and built.
+ </para>
+
+ <para>
+ While the kernel Metadata syntax does not enforce any logical
+ separation of configuration fragments, patches, features or kernel
+ types, best practices dictate a logical separation of these types
+ of Metadata.
+ The following Metadata file hierarchy is recommended:
+ <literallayout class='monospaced'>
+ <replaceable>base</replaceable>/
+ bsp/
+ cfg/
+ features/
+ ktypes/
+ patches/
+ </literallayout>
+ </para>
+
+ <para>
+ The <filename>bsp</filename> directory contains the
+ <link linkend='bsp-descriptions'>BSP descriptions</link>.
+ The remaining directories all contain "features".
+ Separating <filename>bsp</filename> from the rest of the structure
+ aids conceptualizing intended usage.
+ </para>
+
+ <para>
+ Use these guidelines to help place your <filename>scc</filename>
+ description files within the structure:
+ <itemizedlist>
+ <listitem><para>If your file contains
+ only configuration fragments, place the file in the
+ <filename>cfg</filename> directory.</para></listitem>
+ <listitem><para>If your file contains
+ only source-code fixes, place the file in the
+ <filename>patches</filename> directory.</para></listitem>
+ <listitem><para>If your file encapsulates
+ a major feature, often combining sources and configurations,
+ place the file in <filename>features</filename> directory.
+ </para></listitem>
+ <listitem><para>If your file aggregates
+ non-hardware configuration and patches in order to define a
+ base kernel policy or major kernel type to be reused across
+ multiple BSPs, place the file in <filename>ktypes</filename>
+ directory.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ These distinctions can easily become blurred - especially as
+ out-of-tree features slowly merge upstream over time.
+ Also, remember that how the description files are placed is
+ a purely logical organization and has no impact on the functionality
+ of the kernel Metadata.
+ There is no impact because all of <filename>cfg</filename>,
+ <filename>features</filename>, <filename>patches</filename>, and
+ <filename>ktypes</filename>, contain "features" as far as the kernel
+ tools are concerned.
+ </para>
+
+ <para>
+ Paths used in kernel Metadata files are relative to
+ <replaceable>base</replaceable>, which is either
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
+ if you are creating Metadata in
+ <link linkend='recipe-space-metadata'>recipe-space</link>,
+ or the top level of
+ <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/yocto-kernel-cache/tree/'><filename>yocto-kernel-cache</filename></ulink>
+ if you are creating
+ <link linkend='metadata-outside-the-recipe-space'>Metadata outside of the recipe-space</link>.
+ </para>
+
+ <section id='configuration'>
+ <title>Configuration</title>
+
+ <para>
+ The simplest unit of kernel Metadata is the configuration-only
+ feature.
+ This feature consists of one or more Linux kernel configuration
+ parameters in a configuration fragment file
+ (<filename>.cfg</filename>) and a <filename>.scc</filename> file
+ that describes the fragment.
+ </para>
+
+ <para>
+ As an example, consider the Symmetric Multi-Processing (SMP)
+ fragment used with the <filename>linux-yocto-4.12</filename>
+ kernel as defined outside of the recipe space (i.e.
+ <filename>yocto-kernel-cache</filename>).
+ This Metadata consists of two files: <filename>smp.scc</filename>
+ and <filename>smp.cfg</filename>.
+ You can find these files in the <filename>cfg</filename> directory
+ of the <filename>yocto-4.12</filename> branch in the
+ <filename>yocto-kernel-cache</filename> Git repository:
+ <literallayout class='monospaced'>
+ cfg/smp.scc:
+ define KFEATURE_DESCRIPTION "Enable SMP for 32 bit builds"
+ define KFEATURE_COMPATIBILITY all
+
+ kconf hardware smp.cfg
+
+ cfg/smp.cfg:
+ CONFIG_SMP=y
+ CONFIG_SCHED_SMT=y
+ # Increase default NR_CPUS from 8 to 64 so that platform with
+ # more than 8 processors can be all activated at boot time
+ CONFIG_NR_CPUS=64
+ # The following is needed when setting NR_CPUS to something
+ # greater than 8 on x86 architectures, it should be automatically
+ # disregarded by Kconfig when using a different arch
+ CONFIG_X86_BIGSMP=y
+ </literallayout>
+ You can find general information on configuration fragment files in
+ the
+ "<link linkend='creating-config-fragments'>Creating Configuration Fragments</link>"
+ section.
+ </para>
+
+ <para>
+ Within the <filename>smp.scc</filename> file, the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-KFEATURE_DESCRIPTION'><filename>KFEATURE_DESCRIPTION</filename></ulink>
+ statement provides a short description of the fragment.
+ Higher level kernel tools use this description.
+ </para>
+
+ <para>
+ Also within the <filename>smp.scc</filename> file, the
+ <filename>kconf</filename> command includes the
+ actual configuration fragment in an <filename>.scc</filename>
+ file, and the "hardware" keyword identifies the fragment as
+ being hardware enabling, as opposed to general policy,
+ which would use the "non-hardware" keyword.
+ The distinction is made for the benefit of the configuration
+ validation tools, which warn you if a hardware fragment
+ overrides a policy set by a non-hardware fragment.
+ <note>
+ The description file can include multiple
+ <filename>kconf</filename> statements, one per fragment.
+ </note>
+ </para>
+
+ <para>
+ As described in the
+ "<link linkend='validating-configuration'>Validating Configuration</link>"
+ section, you can use the following BitBake command to audit your
+ configuration:
+ <literallayout class='monospaced'>
+ $ bitbake linux-yocto -c kernel_configcheck -f
+ </literallayout>
+ </para>
+ </section>
+
+ <section id='patches'>
+ <title>Patches</title>
+
+ <para>
+ Patch descriptions are very similar to configuration fragment
+ descriptions, which are described in the previous section.
+ However, instead of a <filename>.cfg</filename> file, these
+ descriptions work with source patches (i.e.
+ <filename>.patch</filename> files).
+ </para>
+
+ <para>
+ A typical patch includes a description file and the patch itself.
+ As an example, consider the build patches used with the
+ <filename>linux-yocto-4.12</filename> kernel as defined outside of
+ the recipe space (i.e. <filename>yocto-kernel-cache</filename>).
+ This Metadata consists of several files:
+ <filename>build.scc</filename> and a set of
+ <filename>*.patch</filename> files.
+ You can find these files in the <filename>patches/build</filename>
+ directory of the <filename>yocto-4.12</filename> branch in the
+ <filename>yocto-kernel-cache</filename> Git repository.
+ </para>
+
+ <para>
+ The following listings show the <filename>build.scc</filename>
+ file and part of the
+ <filename>modpost-mask-trivial-warnings.patch</filename> file:
+ <literallayout class='monospaced'>
+ patches/build/build.scc:
+ patch arm-serialize-build-targets.patch
+ patch powerpc-serialize-image-targets.patch
+ patch kbuild-exclude-meta-directory-from-distclean-processi.patch
+
+ # applied by kgit
+ # patch kbuild-add-meta-files-to-the-ignore-li.patch
+
+ patch modpost-mask-trivial-warnings.patch
+ patch menuconfig-check-lxdiaglog.sh-Allow-specification-of.patch
+
+ patches/build/modpost-mask-trivial-warnings.patch:
+ From bd48931bc142bdd104668f3a062a1f22600aae61 Mon Sep 17 00:00:00 2001
+ From: Paul Gortmaker <paul.gortmaker@windriver.com>
+ Date: Sun, 25 Jan 2009 17:58:09 -0500
+ Subject: [PATCH] modpost: mask trivial warnings
+
+ Newer HOSTCC will complain about various stdio fcns because
+ .
+ .
+ .
+ char *dump_write = NULL, *files_source = NULL;
+ int opt;
+ --
+ 2.10.1
+
+ generated by cgit v0.10.2 at 2017-09-28 15:23:23 (GMT)
+ </literallayout>
+ The description file can include multiple patch statements where
+ each statement handles a single patch.
+ In the example <filename>build.scc</filename> file, five patch
+ statements exist for the five patches in the directory.
+ </para>
+
+ <para>
+ You can create a typical <filename>.patch</filename> file using
+ <filename>diff -Nurp</filename> or
+ <filename>git format-patch</filename> commands.
+ For information on how to create patches, see the
+ "<link linkend='using-devtool-to-patch-the-kernel'>Using <filename>devtool</filename> to Patch the Kernel</link>"
+ and
+ "<link linkend='using-traditional-kernel-development-to-patch-the-kernel'>Using Traditional Kernel Development to Patch the Kernel</link>"
+ sections.
+ </para>
+ </section>
+
+ <section id='features'>
+ <title>Features</title>
+
+ <para>
+ Features are complex kernel Metadata types that consist
+ of configuration fragments, patches, and possibly other feature
+ description files.
+ As an example, consider the following generic listing:
+ <literallayout class='monospaced'>
+ features/<replaceable>myfeature</replaceable>.scc
+ define KFEATURE_DESCRIPTION "Enable <replaceable>myfeature</replaceable>"
+
+ patch 0001-<replaceable>myfeature</replaceable>-core.patch
+ patch 0002-<replaceable>myfeature</replaceable>-interface.patch
+
+ include cfg/<replaceable>myfeature</replaceable>_dependency.scc
+ kconf non-hardware <replaceable>myfeature</replaceable>.cfg
+ </literallayout>
+ This example shows how the <filename>patch</filename> and
+ <filename>kconf</filename> commands are used as well as
+ how an additional feature description file is included with
+ the <filename>include</filename> command.
+ </para>
+
+ <para>
+ Typically, features are less granular than configuration
+ fragments and are more likely than configuration fragments
+ and patches to be the types of things you want to specify
+ in the <filename>KERNEL_FEATURES</filename> variable of the
+ Linux kernel recipe.
+ See the "<link linkend='using-kernel-metadata-in-a-recipe'>Using Kernel Metadata in a Recipe</link>"
+ section earlier in the manual.
+ </para>
+ </section>
+
+ <section id='kernel-types'>
+ <title>Kernel Types</title>
+
+ <para>
+ A kernel type defines a high-level kernel policy by
+ aggregating non-hardware configuration fragments with
+ patches you want to use when building a Linux kernel of a
+ specific type (e.g. a real-time kernel).
+ Syntactically, kernel types are no different than features
+ as described in the "<link linkend='features'>Features</link>"
+ section.
+ The
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-LINUX_KERNEL_TYPE'><filename>LINUX_KERNEL_TYPE</filename></ulink>
+ variable in the kernel recipe selects the kernel type.
+ For example, in the <filename>linux-yocto_4.12.bb</filename>
+ kernel recipe found in
+ <filename>poky/meta/recipes-kernel/linux</filename>, a
+ <ulink url='&YOCTO_DOCS_BB_URL;#require-inclusion'><filename>require</filename></ulink>
+ directive includes the
+ <filename>poky/meta/recipes-kernel/linux/linux-yocto.inc</filename>
+ file, which has the following statement that defines the default
+ kernel type:
+ <literallayout class='monospaced'>
+ LINUX_KERNEL_TYPE ??= "standard"
+ </literallayout>
+ </para>
+
+ <para>
+ Another example would be the real-time kernel (i.e.
+ <filename>linux-yocto-rt_4.12.bb</filename>).
+ This kernel recipe directly sets the kernel type as follows:
+ <literallayout class='monospaced'>
+ LINUX_KERNEL_TYPE = "preempt-rt"
+ </literallayout>
+ <note>
+ You can find kernel recipes in the
+ <filename>meta/recipes-kernel/linux</filename> directory of the
+ <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
+ (e.g. <filename>poky/meta/recipes-kernel/linux/linux-yocto_4.12.bb</filename>).
+ See the "<link linkend='using-kernel-metadata-in-a-recipe'>Using Kernel Metadata in a Recipe</link>"
+ section for more information.
+ </note>
+ </para>
+
+ <para>
+ Three kernel types ("standard", "tiny", and "preempt-rt") are
+ supported for Linux Yocto kernels:
+ <itemizedlist>
+ <listitem><para>"standard":
+ Includes the generic Linux kernel policy of the Yocto
+ Project linux-yocto kernel recipes.
+ This policy includes, among other things, which file
+ systems, networking options, core kernel features, and
+ debugging and tracing options are supported.
+ </para></listitem>
+ <listitem><para>"preempt-rt":
+ Applies the <filename>PREEMPT_RT</filename>
+ patches and the configuration options required to
+ build a real-time Linux kernel.
+ This kernel type inherits from the "standard" kernel type.
+ </para></listitem>
+ <listitem><para>"tiny":
+ Defines a bare minimum configuration meant to serve as a
+ base for very small Linux kernels.
+ The "tiny" kernel type is independent from the "standard"
+ configuration.
+ Although the "tiny" kernel type does not currently include
+ any source changes, it might in the future.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ For any given kernel type, the Metadata is defined by the
+ <filename>.scc</filename> (e.g. <filename>standard.scc</filename>).
+ Here is a partial listing for the <filename>standard.scc</filename>
+ file, which is found in the <filename>ktypes/standard</filename>
+ directory of the <filename>yocto-kernel-cache</filename> Git
+ repository:
+ <literallayout class='monospaced'>
+ # Include this kernel type fragment to get the standard features and
+ # configuration values.
+
+ # Note: if only the features are desired, but not the configuration
+ # then this should be included as:
+ # include ktypes/standard/standard.scc nocfg
+ # if no chained configuration is desired, include it as:
+ # include ktypes/standard/standard.scc nocfg inherit
+
+
+
+ include ktypes/base/base.scc
+ branch standard
+
+ kconf non-hardware standard.cfg
+
+ include features/kgdb/kgdb.scc
+ .
+ .
+ .
+
+ include cfg/net/ip6_nf.scc
+ include cfg/net/bridge.scc
+
+ include cfg/systemd.scc
+
+ include features/rfkill/rfkill.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
+ <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/yocto-kernel-cache/tree/bsp'><filename>yocto-kernel-cache</filename></ulink>
+ 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 overviews the BSP description structure, the
+ aggregation concepts, and presents a detailed example using
+ a BSP supported by the Yocto Project (i.e. BeagleBone Board).
+ For complete information on BSP layer file hierarchy, see the
+ <ulink url='&YOCTO_DOCS_BSP_URL;'>Yocto Project Board Support Package (BSP) Developer's Guide</ulink>.
+ </para>
+
+ <section id='bsp-description-file-overview'>
+ <title>Overview</title>
+
+ <para>
+ For simplicity, consider the following root BSP layer
+ description files for the BeagleBone board.
+ These files employ both a structure and naming convention
+ for consistency.
+ The naming convention for the file is as follows:
+ <literallayout class='monospaced'>
+ <replaceable>bsp_root_name</replaceable>-<replaceable>kernel_type</replaceable>.scc
+ </literallayout>
+ Here are some example root layer BSP filenames for the
+ BeagleBone Board BSP, which is supported by the Yocto Project:
+ <literallayout class='monospaced'>
+ beaglebone-standard.scc
+ beaglebone-preempt-rt.scc
+ </literallayout>
+ Each file uses the root name (i.e "beaglebone") BSP name
+ followed by the kernel type.
+ </para>
+
+ <para>
+ Examine the <filename>beaglebone-standard.scc</filename>
+ file:
+ <literallayout class='monospaced'>
+ define KMACHINE beaglebone
+ define KTYPE standard
+ define KARCH arm
+
+ include ktypes/standard/standard.scc
+ branch beaglebone
+
+ include beaglebone.scc
+
+ # default policy for standard kernels
+ include features/latencytop/latencytop.scc
+ include features/profiling/profiling.scc
+ </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 example supports the "beaglebone" machine for the
+ "standard" kernel and the "arm" 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 the kernel type defined in your kernel
+ Metadata as it is here, you only need to ensure that the
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-LINUX_KERNEL_TYPE'><filename>LINUX_KERNEL_TYPE</filename></ulink>
+ variable in the kernel recipe and the
+ <filename>KTYPE</filename> variable in the BSP description
+ file match.
+ </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/standard.scc
+ </literallayout>
+ This file 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>
+ You can see that in the BeagleBone example with the following:
+ <literallayout class='monospaced'>
+ include beaglebone.scc
+ </literallayout>
+ For information on how to break a complete
+ <filename>.config</filename> file into the various
+ configuration fragments, see the
+ "<link linkend='creating-config-fragments'>Creating Configuration Fragments</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>
+ The BeagleBone example does not include these types of
+ configurations.
+ However, the Malta 32-bit board does ("mti-malta32").
+ Here is the <filename>mti-malta32-le-standard.scc</filename>
+ file:
+ <literallayout class='monospaced'>
+ define KMACHINE mti-malta32-le
+ define KMACHINE qemumipsel
+ define KTYPE standard
+ define KARCH mips
+
+ include ktypes/standard/standard.scc
+ branch mti-malta32
+
+ include mti-malta32.scc
+ kconf hardware mti-malta32-le.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 given the
+ <filename>linux-yocto-4.4</filename> branch of the
+ <filename>yocto-kernel-cache</filename> (i.e.
+ <filename>yocto-kernel-cache/bsp/minnow/minnow.scc</filename>):
+ <note>
+ Although the Minnow Board BSP is unused, the Metadata
+ remains and is being used here just as an example.
+ </note>
+ <literallayout class='monospaced'>
+ 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 (i.e. <filename>minnow-standard.scc</filename>:
+ <literallayout class='monospaced'>
+ 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 (i.e. <filename>minnow-tiny.scc</filename>):
+ <literallayout class='monospaced'>
+ 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:
+ <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>.
+ Of these variables, only <filename>KTYPE</filename>
+ has changed to specify the "tiny" kernel type.
+ </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 "type=kmeta" 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_4.12.bb</filename>
+ kernel recipe:
+ <literallayout class='monospaced'>
+ SRC_URI = "git://git.yoctoproject.org/linux-yocto-4.12.git;name=machine;branch=${KBRANCH}; \
+ git://git.yoctoproject.org/yocto-kernel-cache;type=kmeta;name=meta;branch=yocto-4.12;destsuffix=${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>
+ If you modify the Metadata, you must not forget to update the
+ <filename>SRCREV</filename> 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
+ Yocto Linux Kernel Git 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
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-KMACHINE'><filename>KMACHINE</filename></ulink>,
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-KTYPE'><filename>KTYPE</filename></ulink>,
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-KARCH'><filename>KARCH</filename></ulink>,
+ and
+ <ulink url='&YOCTO_DOCS_REF_URL;#var-KFEATURE_DESCRIPTION'><filename>KFEATURE_DESCRIPTION</filename></ulink>.
+ </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
+-->