documentation/bsp-guide/bsp.xml: Updated the Linux Kernel Configuration section

These changes are another round of edits from Tom Z.

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>

1 files changed, 63 insertions, 26 deletions

diff --git a/documentation/bsp-guide/bsp.xml b/documentation/bsp-guide/bsp.xml
index 75640cc58c..ff8a4818f8 100644
--- a/documentation/bsp-guide/bsp.xml
+++ b/documentation/bsp-guide/bsp.xml
@@ -324,21 +324,22 @@ meta-<bsp_name>/recipes-kernel/linux/linux-wrs_git.bbappend
             <para>
                 For your BSP you typically want to use an existing Poky kernel found in the 
                 Poky repository at <filename class='directory'>meta/recipes-kernel/kernel</filename>.
-                You can append your specific changes to the kernel by using a 
-                <filename>.bbappend</filename> file, which is located in the 
-                <filename class='directory'>meta-&lt;bsp_name&gt;/recipes-kernel/linux</filename>
+                You can append your specific changes to the kernel recipe by using an append file, 
+                which is located in the 
+                <filename class='directory'>meta-&lt;bsp_name&gt;/recipes-kernel/linux</filename> 
                 directory.
             </para>
             <para>
-                Consider a BSP that uses the <filename>linux-yocto-stable_git.bb</filename> kernel.
-                You would use the <filename>linux-yocto-stable_git.bbappend</filename> file to add 
+                Consider a BSP that uses the <filename>linux-yocto-stable_git.bb</filename> kernel, 
+                which is the preferred kernel to use for developing a new BSP using the Yocto Project.
+                You would use the <filename>linux-yocto-stable_git.bbappend</filename> file to append 
                 specific BSP settings to the kernel, thus configuring the kernel for your particular BSP.
             </para>
             <para>
                 Consider an example for the existing "crownbay" BSP.
-                The <filename>.bbaappend</filename> file used for the "crownbay" BSP is:
+                The append file used for the "crownbay" BSP is:
                 <programlisting>
-meta-crownbay/recipes-kernel/linux/linux-wrs_git.bbappend
+meta-crownbay/recipes-kernel/linux/linux-yocto-stable_git.bbappend
                 </programlisting>
                 The file contains the following:
                 <programlisting>
@@ -346,31 +347,67 @@ FILESEXTRAPATHS := "${THISDIR}/${PN}"
 COMPATIBLE_MACHINE_crownbay = "cronwbay"
 KMACHINE_crownbay = "crownbay"
                 </programlisting>
-                This <filename>.bbappend</filename> file adds "crownbay" as a compatible machine,
+                This append file adds "crownbay" as a compatible machine,
                 and additionally sets a Yocto Kernel-specific variable that identifies the name of the 
                 BSP branch to use in the GIT repository to find configuration information.
             </para>
-            <note><para>
-                For an established BSP the configuration information is incorporated directly into the 
-                git tree.
-                For a new BSP, however, the <filename>.bbappend</filename> file needs to 
-                include its own set of configuration options in a file called 
-                <filename>defconfig</filename> located in a directory that matches the recipe name.
+            <para>
+                One thing missing in this particular BSP, which you will typically need when 
+                developing a BSP, is the kernel configuration (.config) 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 append file and having the same name 
+                as the kernel.
+                With all these conditions met simply reference those files in a SRC_URI statement in the append 
+                file.
+            </para>
+            <para>
+                For example, suppose you had a set of configuration options in a file called 
+                <filename>defonfig</filename>.  
+                If you put that file inside a directory named 
+                <filename class='directory'>/linux-yocto-stable_git</filename> and then added 
+                a SRC_URI statement such as the following to the append file, those configuration
+                options will be picked up and applied when the kernel is built.
                 <programlisting>
 SRC_URI += "file://defconfig"
                 </programlisting>
-                Once a BSP is committed, the Yocto kernel maintainer moves this configuration information
-                into the git tree so that the <filename>.bbappend</filename> file does not need to locate
-                its own configuration options.
-                Again, the initial configuration options using the SRC_URI are put into a 
-                directory named 
-                <filename class='directory'>meta-&lt;bsp_name&gt;/recipes/linux/linux-yocto-stable</filename>.
-            </para>
-            <para>
-                 You can find more information about creating a BSP that is based on an existing similar
-                 BSP by reading the "Creating a BSP Based on an Existing Similar BSP" section in the 
-                 "<ulink url="http://www.yoctoproject.org/community/documentation">Yocto Project
-                 Kernel Architecture and Use Manual</ulink>".
+            </para>
+            <para>
+                As mentioned earlier, you can group related configurations into multiple files and 
+                name them all in the SRC_URI statement as well.
+                For example, you could group separate configurations specifically for ethernet and graphics
+                into their own files and add those by using a SRC_URI statement like the 
+                following in your append file:
+                <programlisting>
+SRC_URI += "file://defconfig \
+            file://eth.cfg \
+            file://gfx.cfg"
+                </programlisting>
+            </para>
+            <para>
+                The FILESEXTRAPATHS variable is boilerplated here in order to make it easy to do that.
+                It basically allows those configuration files to be found by the build process.
+            </para>
+            <note><para>
+                Other methods exist to accomplish grouping and defining configuration options.
+                For example, you could directly add configuration options to the Yocto kernel 
+                <filename class='directory'>wrs_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. 
+                For information on how to add these configurations directly, see the 
+                "Yocto Project Kernel Architecture and Use Manual" on the 
+                <ulink url="http://yoctoproject.org/community/documentation">Yocto Project website
+                Documentation Page</ulink> 
+            </para>
+            <para>
+                In general, however, the Yocto Project maintainers take care of moving the SRC_URI-specified 
+                configuration options to the <filename class='directory'>wrs_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 manintainers 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>