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>

1 files changed, 227 insertions, 163 deletions

diff --git a/documentation/kernel-dev/kernel-dev-advanced.xml b/documentation/kernel-dev/kernel-dev-advanced.xml
index 1c1b6366db..434c01fafb 100644
--- a/documentation/kernel-dev/kernel-dev-advanced.xml
+++ b/documentation/kernel-dev/kernel-dev-advanced.xml
@@ -524,170 +524,219 @@
         <title>BSP Descriptions</title>
 
         <para>
-            BSP descriptions combine kernel types with hardware-specific
-            features.
-            The hardware-specific portion is typically defined
-            independently, and then aggregated with each supported kernel
-            type.
-            Consider this simple BSP description that supports the
-            <replaceable>mybsp</replaceable> machine:
-            <literallayout class='monospaced'>
-     <replaceable>mybsp</replaceable>.scc:
-        define KMACHINE <replaceable>mybsp</replaceable>
-        define KTYPE standard
-        define KARCH i386
-
-        kconf <replaceable>mybsp</replaceable>.cfg
-            </literallayout>
-            Every BSP description 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.
+            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>
-                Future versions of the tooling make the specification of
-                <filename>KTYPE</filename> in the BSP optional.
+                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>
-            If you did want to separate your kernel policy from your
-            hardware configuration, you could do so by specifying a kernel
-            type, such as "standard" and including that description file
-            in the BSP description file.
-            See the "<link linkend='kernel-types'>Kernel Types</link>" section
-            for more information.
+            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>
 
-        <para>
-            You might also have multiple hardware configurations that you
-            aggregate into a single hardware description file that you
-            could include in the BSP description file, rather than referencing
-            a single <filename>.cfg</filename> file.
-            Consider the following:
-            <literallayout class='monospaced'>
-     <replaceable>mybsp</replaceable>.scc:
-        define KMACHINE mybsp
-        define KTYPE standard
-        define KARCH i386
-
-        include standard.scc
-        include <replaceable>mybsp</replaceable>-hw.scc
-            </literallayout>
-        </para>
+        <section id='bsp-description-file-overview'>
+            <title>Overview</title>
 
-        <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
-            <filename>.config</filename> file into the various
-            configuration fragments, see the
-            "<link linkend='generating-configuration-files'>Generating Configuration Files</link>"
-            section.
-        </para>
+            <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>
-            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-3.19</filename>
-            Git repository:
-            <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 cfg/timer/rtc.scc
-        include features/leds/leds.scc
-        include features/spi/spidev.scc
-        include features/i2c/i2cdev.scc
-
-        # Earlyprintk and port debug requires 8250
-        kconf hardware cfg/8250.cfg
-
-        kconf hardware minnow.cfg
-        kconf hardware minnow-dev.cfg
-            </literallayout>
-        </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>
-            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 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
+            <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>
 
-        include ktypes/standard
+            <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>
 
-        include minnow.scc
+            <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>
 
-        # 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
+            <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>
 
-        # The following should really be in standard.scc
-        # USB live-image support
-        include cfg/usb-mass-storage.scc
-        include cfg/boot-live.scc
+        <section id='bsp-description-file-example-minnow'>
+            <title>Example</title>
 
-        # Basic profiling
-        include features/latencytop/latencytop.scc
-        include features/profiling/profiling.scc
+            <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>
 
-        # 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 hardware enablements for the BSP that is common to all
-            kernel types.
-            Using this command significantly reduces duplication.
-        </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'>
+            <para>
+                Now consider the "minnow" description for the "tiny" kernel
+                type:
+                <literallayout class='monospaced'>
      minnow-tiny.scc:
         define KMACHINE minnow
         define KTYPE tiny
@@ -696,22 +745,24 @@
         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>
+                </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>
+            <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>
 
@@ -795,6 +846,18 @@
             value when changing the content of files not explicitly listed
             in the <filename>SRC_URI</filename>.
         </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 id='metadata-outside-the-recipe-space'>
@@ -817,7 +880,8 @@
             <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.
+            <filename>SRC_URI</filename> statement used in a recipe (e.g.
+            see the previous section).
         </para>
 
         <para>