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bsp-guide, kernel-dev: Updates to how kernel metadata is found 

Fixes [YOCTO #10946]

There was insufficient information in the combination of the
BSP Guide and the Kernel Development Manual on just how to locate
and use kernel metadata.

 * bsp-guide - Removed the detailed append file example for the
   kernel recipe.  This is moved now to the chapter in the kernel
   manual that describes append files.

 * kernel-dev - Placed the example from the BSP Guide into the
   section that describes kernel append files.  Cleaned up some
   terminology issues throughout chapter 3.  Added information
   about how BitBake picks up kernel metadata when the metadata
   is in a hierarchical directory and not just a simple *.scc
   file.

(From yocto-docs rev: 1048acb7127e77ca9c1f524a208fe25344fcb57c)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark 2017-03-27 09:17:08 -07:00 committed by Richard Purdie
parent 730617f8d0
commit ed0d609c7c
3 changed files with 635 additions and 542 deletions
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182
documentation/bsp-guide/bsp.xml
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@ -376,6 +376,7 @@
<section id="bsp-filelayout-readme"> <section id="bsp-filelayout-readme">
<title>README File</title> <title>README File</title>
<para> <para>
You can find this file in the BSP Layer at: You can find this file in the BSP Layer at:
<literallayout class='monospaced'> <literallayout class='monospaced'>
@ -400,6 +401,7 @@
<section id="bsp-filelayout-readme-sources"> <section id="bsp-filelayout-readme-sources">
<title>README.sources File</title> <title>README.sources File</title>
<para> <para>
You can find this file in the BSP Layer at: You can find this file in the BSP Layer at:
<literallayout class='monospaced'> <literallayout class='monospaced'>
@ -428,6 +430,7 @@
<section id="bsp-filelayout-binary"> <section id="bsp-filelayout-binary">
<title>Pre-built User Binaries</title> <title>Pre-built User Binaries</title>
<para> <para>
You can find these files in the BSP Layer at: You can find these files in the BSP Layer at:
<literallayout class='monospaced'> <literallayout class='monospaced'>
@ -461,6 +464,7 @@
<section id='bsp-filelayout-layer'> <section id='bsp-filelayout-layer'>
<title>Layer Configuration File</title> <title>Layer Configuration File</title>
<para> <para>
You can find this file in the BSP Layer at: You can find this file in the BSP Layer at:
<literallayout class='monospaced'> <literallayout class='monospaced'>
@ -526,6 +530,7 @@
<section id="bsp-filelayout-machine"> <section id="bsp-filelayout-machine">
<title>Hardware Configuration Options</title> <title>Hardware Configuration Options</title>
<para> <para>
You can find these files in the BSP Layer at: You can find these files in the BSP Layer at:
<literallayout class='monospaced'> <literallayout class='monospaced'>
@ -585,6 +590,7 @@
<section id='bsp-filelayout-misc-recipes'> <section id='bsp-filelayout-misc-recipes'>
<title>Miscellaneous BSP-Specific Recipe Files</title> <title>Miscellaneous BSP-Specific Recipe Files</title>
<para> <para>
You can find these files in the BSP Layer at: You can find these files in the BSP Layer at:
<literallayout class='monospaced'> <literallayout class='monospaced'>
@ -627,6 +633,7 @@
<section id='bsp-filelayout-recipes-graphics'> <section id='bsp-filelayout-recipes-graphics'>
<title>Display Support Files</title> <title>Display Support Files</title>
<para> <para>
You can find these files in the BSP Layer at: You can find these files in the BSP Layer at:
<literallayout class='monospaced'> <literallayout class='monospaced'>
@ -644,6 +651,7 @@
<section id='bsp-filelayout-kernel'> <section id='bsp-filelayout-kernel'>
<title>Linux Kernel Configuration</title> <title>Linux Kernel Configuration</title>
<para> <para>
You can find these files in the BSP Layer at: You can find these files in the BSP Layer at:
<literallayout class='monospaced'> <literallayout class='monospaced'>
@ -652,29 +660,39 @@
</para> </para>
<para> <para>
These files append your specific changes to the main kernel recipe you are using. These files append machine-specific changes to the main
kernel recipe you are using.
</para> </para>
<para> <para>
For your BSP, you typically want to use an existing Yocto Project kernel recipe found in the For your BSP, you typically want to use an existing Yocto
Project kernel recipe found in the
<ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink> <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>
at <filename>meta/recipes-kernel/linux</filename>. at <filename>meta/recipes-kernel/linux</filename>.
You can append your specific changes to the kernel recipe by using a You can append machine-specific changes to the kernel recipe
similarly named append file, which is located in the BSP Layer (e.g. by using a similarly named append file, which is located in
the <filename>meta-<replaceable>bsp_name</replaceable>/recipes-kernel/linux</filename> directory). the BSP Layer for your target device (e.g. the
<filename>meta-<replaceable>bsp_name</replaceable>/recipes-kernel/linux</filename> directory).
</para> </para>
<para> <para>
Suppose you are using the <filename>linux-yocto_4.4.bb</filename> recipe to build Suppose you are using the <filename>linux-yocto_4.4.bb</filename>
the kernel. recipe to build the kernel.
In other words, you have selected the kernel in your In other words, you have selected the kernel in your
<replaceable>bsp_name</replaceable><filename>.conf</filename> file by adding these types <replaceable>bsp_name</replaceable><filename>.conf</filename>
of statements: file by adding
<ulink url='&YOCTO_DOCS_REF_URL;#var-PREFERRED_PROVIDER'><filename>PREFERRED_PROVIDER</filename></ulink>
and
<ulink url='&YOCTO_DOCS_REF_URL;#var-PREFERRED_VERSION'><filename>PREFERRED_VERSION</filename></ulink>
statements as follows:
<literallayout class='monospaced'> <literallayout class='monospaced'>
PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto" PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
PREFERRED_VERSION_linux-yocto ?= "4.4%" PREFERRED_VERSION_linux-yocto ?= "4.4%"
</literallayout> </literallayout>
<note> <note>
When the preferred provider is assumed by default, the When the preferred provider is assumed by default, the
<filename>PREFERRED_PROVIDER</filename> statement does not appear in the <filename>PREFERRED_PROVIDER</filename>
statement does not appear in the
<replaceable>bsp_name</replaceable><filename>.conf</filename> file. <replaceable>bsp_name</replaceable><filename>.conf</filename> file.
</note> </note>
You would use the <filename>linux-yocto_4.4.bbappend</filename> You would use the <filename>linux-yocto_4.4.bbappend</filename>
@ -683,146 +701,12 @@
</para> </para>
<para> <para>
As an example, consider the following append file You can find more information on what your append file
used by the BSPs in <filename>meta-yocto-bsp</filename>: should contain in the
<literallayout class='monospaced'> "<ulink url='&YOCTO_DOCS_KERNEL_URL;#creating-the-append-file'>Creating the Append File</ulink>"
meta-yocto-bsp/recipes-kernel/linux/linux-yocto_4.4.bbappend section in the Yocto Project Linux Kernel Development
</literallayout> Manual.
The following listing shows the file.
Be aware that the actual commit ID strings in this
example listing might be different than the actual strings
in the file from the <filename>meta-yocto-bsp</filename>
layer upstream.
<literallayout class='monospaced'>
KBRANCH_genericx86 = "standard/base"
KBRANCH_genericx86-64 = "standard/base"
KMACHINE_genericx86 ?= "common-pc"
KMACHINE_genericx86-64 ?= "common-pc-64"
KBRANCH_edgerouter = "standard/edgerouter"
KBRANCH_beaglebone = "standard/beaglebone"
KBRANCH_mpc8315e-rdb = "standard/fsl-mpc8315e-rdb"
SRCREV_machine_genericx86 ?= "ff4c4ef15b51f45b9106d71bf1f62fe7c02e63c2"
SRCREV_machine_genericx86-64 ?= "ff4c4ef15b51f45b9106d71bf1f62fe7c02e63c2"
SRCREV_machine_edgerouter ?= "ff4c4ef15b51f45b9106d71bf1f62fe7c02e63c2"
SRCREV_machine_beaglebone ?= "ff4c4ef15b51f45b9106d71bf1f62fe7c02e63c2"
SRCREV_machine_mpc8315e-rdb ?= "df00877ef9387b38b9601c82db57de2a1b23ce53"
COMPATIBLE_MACHINE_genericx86 = "genericx86"
COMPATIBLE_MACHINE_genericx86-64 = "genericx86-64"
COMPATIBLE_MACHINE_edgerouter = "edgerouter"
COMPATIBLE_MACHINE_beaglebone = "beaglebone"
COMPATIBLE_MACHINE_mpc8315e-rdb = "mpc8315e-rdb"
LINUX_VERSION_genericx86 = "4.4.3"
LINUX_VERSION_genericx86-64 = "4.4.3"
</literallayout>
This append file contains statements used to support
several BSPs that ship with the Yocto Project.
The file defines machines using the
<ulink url='&YOCTO_DOCS_REF_URL;#var-COMPATIBLE_MACHINE'><filename>COMPATIBLE_MACHINE</filename></ulink>
variable and uses the
<ulink url='&YOCTO_DOCS_REF_URL;#var-KMACHINE'><filename>KMACHINE</filename></ulink>
variable to ensure the machine name used by the OpenEmbedded
build system maps to the machine name used by the Linux Yocto
kernel.
The file also uses the optional
<ulink url='&YOCTO_DOCS_REF_URL;#var-KBRANCH'><filename>KBRANCH</filename></ulink>
variable to ensure the build process uses the
appropriate kernel branch.
</para> </para>
<para>
Although this particular example does not use it, the
<ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_FEATURES'><filename>KERNEL_FEATURES</filename></ulink>
variable could be used to enable features specific to
the kernel.
The append file points to specific commits in the
<ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>
Git repository and the <filename>meta</filename> Git repository
branches to identify the exact kernel needed to build the
BSP.
</para>
<para>
One thing missing in this particular BSP, which you will
typically need when developing a BSP, is the kernel configuration
file (<filename>.config</filename>) for your BSP.
When developing a BSP, you probably have a kernel configuration
file or a set of kernel configuration files that, when taken
together, define the kernel configuration for your BSP.
You can accomplish this definition by putting the configurations
in a file or a set of files inside a directory located at the
same level as your kernel's append file and having the same
name as the kernel's main recipe file.
With all these conditions met, simply reference those files in the
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
statement in the append file.
</para>
<para>
For example, suppose you had some configuration options
in a file called <filename>network_configs.cfg</filename>.
You can place that file inside a directory named
<filename>linux-yocto</filename> and then add
a <filename>SRC_URI</filename> statement such as the
following to the append file.
When the OpenEmbedded build system builds the kernel, the
configuration options are picked up and applied.
<literallayout class='monospaced'>
SRC_URI += "file://network_configs.cfg"
</literallayout>
</para>
<para>
To group related configurations into multiple files, you
perform a similar procedure.
Here is an example that groups separate configurations
specifically for Ethernet and graphics into their own
files and adds the configurations by using a
<filename>SRC_URI</filename> statement like the following
in your append file:
<literallayout class='monospaced'>
SRC_URI += "file://myconfig.cfg \
file://eth.cfg \
file://gfx.cfg"
</literallayout>
</para>
<para>
Another variable you can use in your kernel recipe append
file is the
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
variable.
When you use this statement, you are extending the locations
used by the OpenEmbedded system to look for files and
patches as the recipe is processed.
</para>
<note>
<para>
Other methods exist to accomplish grouping and defining configuration options.
For example, if you are working with a local clone of the kernel repository,
you could checkout the kernel's <filename>meta</filename> branch, make your changes,
and then push the changes to the local bare clone of the kernel.
The result is that you directly add configuration options to the
<filename>meta</filename> branch for your BSP.
The configuration options will likely end up in that location anyway if the BSP gets
added to the Yocto Project.
</para>
<para>
In general, however, the Yocto Project maintainers take care of moving the
<filename>SRC_URI</filename>-specified
configuration options to the kernel's <filename>meta</filename> branch.
Not only is it easier for BSP developers to not have to worry about putting those
configurations in the branch, but having the maintainers do it allows them to apply
'global' knowledge about the kinds of common configuration options multiple BSPs in
the tree are typically using.
This allows for promotion of common configurations into common features.
</para>
</note>
</section> </section>
</section> </section>

162
documentation/kernel-dev/kernel-dev-advanced.xml
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@ -524,22 +524,66 @@
<title>BSP Descriptions</title> <title>BSP Descriptions</title>
<para> <para>
BSP descriptions combine kernel types with hardware-specific BSP descriptions (i.e. <filename>*.scc</filename> files)
features. combine kernel types with hardware-specific features.
The hardware-specific portion is typically defined The hardware-specific Metadata is typically defined
independently, and then aggregated with each supported kernel independently in the BSP layer, and then aggregated with each
type. supported kernel type.
Consider this simple BSP description that supports the <note>
<replaceable>mybsp</replaceable> machine: 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'> <literallayout class='monospaced'>
<replaceable>mybsp</replaceable>.scc:
define KMACHINE <replaceable>mybsp</replaceable> define KMACHINE <replaceable>mybsp</replaceable>
define KTYPE standard define KTYPE standard
define KARCH i386 define KARCH i386
kconf <replaceable>mybsp</replaceable>.cfg include ktypes/standard
include <replaceable>mybsp</replaceable>.scc
kconf hardware <replaceable>mybsp</replaceable>-<replaceable>extra</replaceable>.cfg
</literallayout> </literallayout>
Every BSP description should define the 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-KMACHINE'><filename>KMACHINE</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-KTYPE'><filename>KTYPE</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> and <ulink url='&YOCTO_DOCS_REF_URL;#var-KARCH'><filename>KARCH</filename></ulink>
@ -553,8 +597,8 @@
<para> <para>
Be aware that a hard link between the Be aware that a hard link between the
<filename>KTYPE</filename> variable and a kernel type <filename>KTYPE</filename> variable and a kernel type description
description file does not exist. file does not exist.
Thus, if you do not have kernel types defined in your kernel Thus, if you do not have kernel types defined in your kernel
Metadata, you only need to ensure that the kernel recipe's 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> <ulink url='&YOCTO_DOCS_REF_URL;#var-LINUX_KERNEL_TYPE'><filename>LINUX_KERNEL_TYPE</filename></ulink>
@ -567,39 +611,26 @@
</para> </para>
<para> <para>
If you did want to separate your kernel policy from your To separate your kernel policy from your hardware configuration,
hardware configuration, you could do so by specifying a kernel you include a kernel type (<filename>ktype</filename>), such as
type, such as "standard" and including that description file "standard".
in the BSP description file. 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 See the "<link linkend='kernel-types'>Kernel Types</link>" section
for more information. for more information.
</para> </para>
<para> <para>
You might also have multiple hardware configurations that you To aggregate common configurations and features specific to the
aggregate into a single hardware description file that you kernel for <replaceable>mybsp</replaceable>, use the following:
could include in the BSP description file, rather than referencing
a single <filename>.cfg</filename> file.
Consider the following:
<literallayout class='monospaced'> <literallayout class='monospaced'>
<replaceable>mybsp</replaceable>.scc: include <replaceable>mybsp</replaceable>.scc
define KMACHINE mybsp
define KTYPE standard
define KARCH i386
include standard.scc
include <replaceable>mybsp</replaceable>-hw.scc
</literallayout> </literallayout>
</para>
<para>
In the above example, <filename>standard.scc</filename>
aggregates all the configuration fragments, patches, and
features that make up your standard kernel policy whereas
<replaceable>mybsp</replaceable><filename>-hw.scc</filename>
aggregates all those necessary
to support the hardware available on the
<replaceable>mybsp</replaceable> machine.
For information on how to break a complete For information on how to break a complete
<filename>.config</filename> file into the various <filename>.config</filename> file into the various
configuration fragments, see the configuration fragments, see the
@ -607,13 +638,29 @@
section. section.
</para> </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> <para>
Many real-world examples are more complex. Many real-world examples are more complex.
Like any other <filename>.scc</filename> file, BSP Like any other <filename>.scc</filename> file, BSP
descriptions can aggregate features. descriptions can aggregate features.
Consider the Minnow BSP definition from the Consider the Minnow BSP definition from the
<filename>linux-yocto-3.19</filename> <filename>linux-yocto-4.4</filename> in the
Git repository: 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'> <literallayout class='monospaced'>
minnow.scc: minnow.scc:
include cfg/x86.scc include cfg/x86.scc
@ -626,10 +673,10 @@
include features/usb/usb-gadgets.scc include features/usb/usb-gadgets.scc
include features/usb/touchscreen-composite.scc include features/usb/touchscreen-composite.scc
include cfg/timer/hpet.scc include cfg/timer/hpet.scc
include cfg/timer/rtc.scc
include features/leds/leds.scc include features/leds/leds.scc
include features/spi/spidev.scc include features/spi/spidev.scc
include features/i2c/i2cdev.scc include features/i2c/i2cdev.scc
include features/mei/mei-txe.scc
# Earlyprintk and port debug requires 8250 # Earlyprintk and port debug requires 8250
kconf hardware cfg/8250.cfg kconf hardware cfg/8250.cfg
@ -646,7 +693,8 @@
BSP as well as several more general configuration BSP as well as several more general configuration
fragments and features enabling hardware found on the fragments and features enabling hardware found on the
machine. machine.
This description file is then included in each of the three This <filename>minnow.scc</filename> description file is then
included in each of the three
"minnow" description files for the supported kernel types "minnow" description files for the supported kernel types
(i.e. "standard", "preempt-rt", and "tiny"). (i.e. "standard", "preempt-rt", and "tiny").
Consider the "minnow" description for the "standard" kernel Consider the "minnow" description for the "standard" kernel
@ -680,13 +728,14 @@
</literallayout> </literallayout>
The <filename>include</filename> command midway through the file The <filename>include</filename> command midway through the file
includes the <filename>minnow.scc</filename> description that includes the <filename>minnow.scc</filename> description that
defines all hardware enablements for the BSP that is common to all defines all enabled hardware for the BSP that is common to
kernel types. all kernel types.
Using this command significantly reduces duplication. Using this command significantly reduces duplication.
</para> </para>
<para> <para>
Now consider the "minnow" description for the "tiny" kernel type: Now consider the "minnow" description for the "tiny" kernel
type:
<literallayout class='monospaced'> <literallayout class='monospaced'>
minnow-tiny.scc: minnow-tiny.scc:
define KMACHINE minnow define KMACHINE minnow
@ -700,9 +749,10 @@
As you might expect, the "tiny" description includes quite a As you might expect, the "tiny" description includes quite a
bit less. bit less.
In fact, it includes only the minimal policy defined by the In fact, it includes only the minimal policy defined by the
"tiny" kernel type and the hardware-specific configuration required "tiny" kernel type and the hardware-specific configuration
for booting the machine along with the most basic functionality of required for booting the machine along with the most basic
the system as defined in the base "minnow" description file. functionality of the system as defined in the base "minnow"
description file.
</para> </para>
<para> <para>
@ -714,6 +764,7 @@
</para> </para>
</section> </section>
</section> </section>
</section>
<section id='kernel-metadata-location'> <section id='kernel-metadata-location'>
<title>Kernel Metadata Location</title> <title>Kernel Metadata Location</title>
@ -795,6 +846,18 @@
value when changing the content of files not explicitly listed value when changing the content of files not explicitly listed
in the <filename>SRC_URI</filename>. in the <filename>SRC_URI</filename>.
</para> </para>
<para>
If the kernel Metadata is in a layer, 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>
<section id='metadata-outside-the-recipe-space'> <section id='metadata-outside-the-recipe-space'>
@ -817,7 +880,8 @@
<filename>${KMETA}</filename>, in this context, is simply used to <filename>${KMETA}</filename>, in this context, is simply used to
name the directory into which the Git fetcher places the Metadata. name the directory into which the Git fetcher places the Metadata.
This behavior is no different than any multi-repository This behavior is no different than any multi-repository
<filename>SRC_URI</filename> statement used in a recipe. <filename>SRC_URI</filename> statement used in a recipe (e.g.
see the previous section).
</para> </para>
<para> <para>

149
documentation/kernel-dev/kernel-dev-common.xml
View File

@ -84,11 +84,11 @@
You also name it accordingly based on the linux-yocto recipe You also name it accordingly based on the linux-yocto recipe
you are using. you are using.
For example, if you are modifying the For example, if you are modifying the
<filename>meta/recipes-kernel/linux/linux-yocto_3.19.bb</filename> <filename>meta/recipes-kernel/linux/linux-yocto_4.4.bb</filename>
recipe, the append file will typically be located as follows recipe, the append file will typically be located as follows
within your custom layer: within your custom layer:
<literallayout class='monospaced'> <literallayout class='monospaced'>
<replaceable>your-layer</replaceable>/recipes-kernel/linux/linux-yocto_3.19.bbappend <replaceable>your-layer</replaceable>/recipes-kernel/linux/linux-yocto_4.4.bbappend
</literallayout> </literallayout>
The append file should initially extend the The append file should initially extend the
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink> <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
@ -114,6 +114,151 @@
<ulink url='&YOCTO_DOCS_BSP_URL;'>Yocto Project Board Support Package (BSP) Developer's Guide</ulink>. <ulink url='&YOCTO_DOCS_BSP_URL;'>Yocto Project Board Support Package (BSP) Developer's Guide</ulink>.
</note> </note>
</para> </para>
<para>
As an example, consider the following append file
used by the BSPs in <filename>meta-yocto-bsp</filename>:
<literallayout class='monospaced'>
meta-yocto-bsp/recipes-kernel/linux/linux-yocto_4.4.bbappend
</literallayout>
The following listing shows the file.
Be aware that the actual commit ID strings in this
example listing might be different than the actual strings
in the file from the <filename>meta-yocto-bsp</filename>
layer upstream.
<literallayout class='monospaced'>
KBRANCH_genericx86 = "standard/base"
KBRANCH_genericx86-64 = "standard/base"
KMACHINE_genericx86 ?= "common-pc"
KMACHINE_genericx86-64 ?= "common-pc-64"
KBRANCH_edgerouter = "standard/edgerouter"
KBRANCH_beaglebone = "standard/beaglebone"
KBRANCH_mpc8315e-rdb = "standard/fsl-mpc8315e-rdb"
SRCREV_machine_genericx86 ?= "ad8b1d659ddd2699ebf7d50ef9de8940b157bfc2"
SRCREV_machine_genericx86-64 ?= "ad8b1d659ddd2699ebf7d50ef9de8940b157bfc2"
SRCREV_machine_edgerouter ?= "cebe1ad56aebd89e0de29412e19433fb441bf13c"
SRCREV_machine_beaglebone ?= "cebe1ad56aebd89e0de29412e19433fb441bf13c"
SRCREV_machine_mpc8315e-rdb ?= "06c0dbdcba374ca7f92a53d69292d6bb7bc9b0f3"
COMPATIBLE_MACHINE_genericx86 = "genericx86"
COMPATIBLE_MACHINE_genericx86-64 = "genericx86-64"
COMPATIBLE_MACHINE_edgerouter = "edgerouter"
COMPATIBLE_MACHINE_beaglebone = "beaglebone"
COMPATIBLE_MACHINE_mpc8315e-rdb = "mpc8315e-rdb"
LINUX_VERSION_genericx86 = "4.4.41"
LINUX_VERSION_genericx86-64 = "4.4.41"
LINUX_VERSION_edgerouter = "4.4.53"
LINUX_VERSION_beaglebone = "4.4.53"
LINUX_VERSION_mpc8315e-rdb = "4.4.53"
</literallayout>
This append file contains statements used to support
several BSPs that ship with the Yocto Project.
The file defines machines using the
<ulink url='&YOCTO_DOCS_REF_URL;#var-COMPATIBLE_MACHINE'><filename>COMPATIBLE_MACHINE</filename></ulink>
variable and uses the
<ulink url='&YOCTO_DOCS_REF_URL;#var-KMACHINE'><filename>KMACHINE</filename></ulink>
variable to ensure the machine name used by the OpenEmbedded
build system maps to the machine name used by the Linux Yocto
kernel.
The file also uses the optional
<ulink url='&YOCTO_DOCS_REF_URL;#var-KBRANCH'><filename>KBRANCH</filename></ulink>
variable to ensure the build process uses the
appropriate kernel branch.
</para>
<para>
Although this particular example does not use it, the
<ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_FEATURES'><filename>KERNEL_FEATURES</filename></ulink>
variable could be used to enable features specific to
the kernel.
The append file points to specific commits in the
<ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>
Git repository and the <filename>meta</filename> Git repository
branches to identify the exact kernel needed to build the
BSP.
</para>
<para>
One thing missing in this particular BSP, which you will
typically need when developing a BSP, is the kernel configuration
file (<filename>.config</filename>) for your BSP.
When developing a BSP, you probably have a kernel configuration
file or a set of kernel configuration files that, when taken
together, define the kernel configuration for your BSP.
You can accomplish this definition by putting the configurations
in a file or a set of files inside a directory located at the
same level as your kernel's append file and having the same
name as the kernel's main recipe file.
With all these conditions met, simply reference those files in the
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
statement in the append file.
</para>
<para>
For example, suppose you had some configuration options
in a file called <filename>network_configs.cfg</filename>.
You can place that file inside a directory named
<filename>linux-yocto</filename> and then add
a <filename>SRC_URI</filename> statement such as the
following to the append file.
When the OpenEmbedded build system builds the kernel, the
configuration options are picked up and applied.
<literallayout class='monospaced'>
SRC_URI += "file://network_configs.cfg"
</literallayout>
</para>
<para>
To group related configurations into multiple files, you
perform a similar procedure.
Here is an example that groups separate configurations
specifically for Ethernet and graphics into their own
files and adds the configurations by using a
<filename>SRC_URI</filename> statement like the following
in your append file:
<literallayout class='monospaced'>
SRC_URI += "file://myconfig.cfg \
file://eth.cfg \
file://gfx.cfg"
</literallayout>
</para>
<para>
Another variable you can use in your kernel recipe append
file is the
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
variable.
When you use this statement, you are extending the locations
used by the OpenEmbedded system to look for files and
patches as the recipe is processed.
</para>
<note>
<para>
Other methods exist to accomplish grouping and defining configuration options.
For example, if you are working with a local clone of the kernel repository,
you could checkout the kernel's <filename>meta</filename> branch, make your changes,
and then push the changes to the local bare clone of the kernel.
The result is that you directly add configuration options to the
<filename>meta</filename> branch for your BSP.
The configuration options will likely end up in that location anyway if the BSP gets
added to the Yocto Project.
</para>
<para>
In general, however, the Yocto Project maintainers take care of moving the
<filename>SRC_URI</filename>-specified
configuration options to the kernel's <filename>meta</filename> branch.
Not only is it easier for BSP developers to not have to worry about putting those
configurations in the branch, but having the maintainers do it allows them to apply
'global' knowledge about the kinds of common configuration options multiple BSPs in
the tree are typically using.
This allows for promotion of common configurations into common features.
</para>
</note>
</section> </section>
<section id='applying-patches'> <section id='applying-patches'>