sphinx: initial sphinx support

This commit is autogenerated pandoc to generate an inital set
of reST files based on DocBook XML files.

A .rst file is generated for each .xml files in all manuals with this
command:

cd <manual>
for i in *.xml; do \
  pandoc -f docbook -t rst --shift-heading-level-by=-1 \
  $i -o $(basename $i .xml).rst \
done

The conversion was done with: pandoc 2.9.2.1-91 (Arch Linux).

Also created an initial top level index file for each document, and
added all 'books' to the top leve index.rst file.

The YP manuals layout is organized as:

Book
  Chapter
    Section
      Section
        Section

Sphinx uses section headers to create the document structure.
ReStructuredText defines sections headers like that:

   To break longer text up into sections, you use section headers. These
   are a single line of text (one or more words) with adornment: an
   underline alone, or an underline and an overline together, in dashes
   "-----", equals "======", tildes "~~~~~~" or any of the
   non-alphanumeric characters = - ` : ' " ~ ^ _ * + # < > that you feel
   comfortable with. An underline-only adornment is distinct from an
   overline-and-underline adornment using the same character. The
   underline/overline must be at least as long as the title text. Be
   consistent, since all sections marked with the same adornment style
   are deemed to be at the same level:

Let's define the following convention when converting from Docbook:

Book                => overline ===   (Title)
  Chapter           => overline ***   (1.)
    Section         => ====           (1.1)
      Section       => ----           (1.1.1)
        Section     => ~~~~           (1.1.1.1)
          Section   => ^^^^           (1.1.1.1.1)

During the conversion with pandoc, we used --shift-heading-level=-1 to
convert most of DocBook headings automatically. However with this
setting, the Chapter header was removed, so I added it back
manually. Without this setting all headings were off by one, which was
more difficult to manually fix.

At least with this change, we now have the same TOC with Sphinx and
DocBook.

(From yocto-docs rev: 3c73d64a476d4423ee4c6808c685fa94d88d7df8)

Signed-off-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 226 insertions, 0 deletions

diff --git a/documentation/kernel-dev/kernel-dev-maint-appx.rst b/documentation/kernel-dev/kernel-dev-maint-appx.rst
new file mode 100644
index 0000000000..4653e51eba
--- /dev/null
+++ b/documentation/kernel-dev/kernel-dev-maint-appx.rst
@@ -0,0 +1,226 @@
+******************
+Kernel Maintenance
+******************
+
+Tree Construction
+=================
+
+This section describes construction of the Yocto Project kernel source
+repositories as accomplished by the Yocto Project team to create Yocto
+Linux kernel repositories. These kernel repositories are found under the
+heading "Yocto Linux Kernel" at `YOCTO_GIT_URL <&YOCTO_GIT_URL;>`__ and
+are shipped as part of a Yocto Project release. The team creates these
+repositories by compiling and executing the set of feature descriptions
+for every BSP and feature in the product. Those feature descriptions
+list all necessary patches, configurations, branches, tags, and feature
+divisions found in a Yocto Linux kernel. Thus, the Yocto Project Linux
+kernel repository (or tree) and accompanying Metadata in the
+``yocto-kernel-cache`` are built.
+
+The existence of these repositories allow you to access and clone a
+particular Yocto Project Linux kernel repository and use it to build
+images based on their configurations and features.
+
+You can find the files used to describe all the valid features and BSPs
+in the Yocto Project Linux kernel in any clone of the Yocto Project
+Linux kernel source repository and ``yocto-kernel-cache`` Git trees. For
+example, the following commands clone the Yocto Project baseline Linux
+kernel that branches off ``linux.org`` version 4.12 and the
+``yocto-kernel-cache``, which contains stores of kernel Metadata: $ git
+clone git://git.yoctoproject.org/linux-yocto-4.12 $ git clone
+git://git.yoctoproject.org/linux-kernel-cache For more information on
+how to set up a local Git repository of the Yocto Project Linux kernel
+files, see the "`Preparing the Build Host to Work on the
+Kernel <#preparing-the-build-host-to-work-on-the-kernel>`__" section.
+
+Once you have cloned the kernel Git repository and the cache of Metadata
+on your local machine, you can discover the branches that are available
+in the repository using the following Git command: $ git branch -a
+Checking out a branch allows you to work with a particular Yocto Linux
+kernel. For example, the following commands check out the
+"standard/beagleboard" branch of the Yocto Linux kernel repository and
+the "yocto-4.12" branch of the ``yocto-kernel-cache`` repository: $ cd
+~/linux-yocto-4.12 $ git checkout -b my-kernel-4.12
+remotes/origin/standard/beagleboard $ cd ~/linux-kernel-cache $ git
+checkout -b my-4.12-metadata remotes/origin/yocto-4.12
+
+.. note::
+
+   Branches in the
+   yocto-kernel-cache
+   repository correspond to Yocto Linux kernel versions (e.g.
+   "yocto-4.12", "yocto-4.10", "yocto-4.9", and so forth).
+
+Once you have checked out and switched to appropriate branches, you can
+see a snapshot of all the kernel source files used to used to build that
+particular Yocto Linux kernel for a particular board.
+
+To see the features and configurations for a particular Yocto Linux
+kernel, you need to examine the ``yocto-kernel-cache`` Git repository.
+As mentioned, branches in the ``yocto-kernel-cache`` repository
+correspond to Yocto Linux kernel versions (e.g. ``yocto-4.12``).
+Branches contain descriptions in the form of ``.scc`` and ``.cfg``
+files.
+
+You should realize, however, that browsing your local
+``yocto-kernel-cache`` repository for feature descriptions and patches
+is not an effective way to determine what is in a particular kernel
+branch. Instead, you should use Git directly to discover the changes in
+a branch. Using Git is an efficient and flexible way to inspect changes
+to the kernel.
+
+.. note::
+
+   Ground up reconstruction of the complete kernel tree is an action
+   only taken by the Yocto Project team during an active development
+   cycle. When you create a clone of the kernel Git repository, you are
+   simply making it efficiently available for building and development.
+
+The following steps describe what happens when the Yocto Project Team
+constructs the Yocto Project kernel source Git repository (or tree)
+found at ` <&YOCTO_GIT_URL;>`__ given the introduction of a new
+top-level kernel feature or BSP. The following actions effectively
+provide the Metadata and create the tree that includes the new feature,
+patch, or BSP:
+
+1. *Pass Feature to the OpenEmbedded Build System:* A top-level kernel
+   feature is passed to the kernel build subsystem. Normally, this
+   feature is a BSP for a particular kernel type.
+
+2. *Locate Feature:* The file that describes the top-level feature is
+   located by searching these system directories:
+
+   -  The in-tree kernel-cache directories, which are located in the
+      ```yocto-kernel-cache`` <&YOCTO_GIT_URL;/cgit/cgit.cgi/yocto-kernel-cache/tree/bsp>`__
+      repository organized under the "Yocto Linux Kernel" heading in the
+      `Yocto Project Source
+      Repositories <http://git.yoctoproject.org/cgit/cgit.cgi>`__.
+
+   -  Areas pointed to by ``SRC_URI`` statements found in kernel recipes
+
+   For a typical build, the target of the search is a feature
+   description in an ``.scc`` file whose name follows this format (e.g.
+   ``beaglebone-standard.scc`` and ``beaglebone-preempt-rt.scc``):
+   bsp_root_name-kernel_type.scc
+
+3. *Expand Feature:* Once located, the feature description is either
+   expanded into a simple script of actions, or into an existing
+   equivalent script that is already part of the shipped kernel.
+
+4. *Append Extra Features:* Extra features are appended to the top-level
+   feature description. These features can come from the
+   ```KERNEL_FEATURES`` <&YOCTO_DOCS_REF_URL;#var-KERNEL_FEATURES>`__
+   variable in recipes.
+
+5. *Locate, Expand, and Append Each Feature:* Each extra feature is
+   located, expanded and appended to the script as described in step
+   three.
+
+6. *Execute the Script:* The script is executed to produce files
+   ``.scc`` and ``.cfg`` files in appropriate directories of the
+   ``yocto-kernel-cache`` repository. These files are descriptions of
+   all the branches, tags, patches and configurations that need to be
+   applied to the base Git repository to completely create the source
+   (build) branch for the new BSP or feature.
+
+7. *Clone Base Repository:* The base repository is cloned, and the
+   actions listed in the ``yocto-kernel-cache`` directories are applied
+   to the tree.
+
+8. *Perform Cleanup:* The Git repositories are left with the desired
+   branches checked out and any required branching, patching and tagging
+   has been performed.
+
+The kernel tree and cache are ready for developer consumption to be
+locally cloned, configured, and built into a Yocto Project kernel
+specific to some target hardware.
+
+.. note::
+
+   -  The generated ``yocto-kernel-cache`` repository adds to the kernel
+      as shipped with the Yocto Project release. Any add-ons and
+      configuration data are applied to the end of an existing branch.
+      The full repository generation that is found in the official Yocto
+      Project kernel repositories at
+      `http://git.yoctoproject.org <&YOCTO_GIT_URL;>`__ is the
+      combination of all supported boards and configurations.
+
+   -  The technique the Yocto Project team uses is flexible and allows
+      for seamless blending of an immutable history with additional
+      patches specific to a deployment. Any additions to the kernel
+      become an integrated part of the branches.
+
+   -  The full kernel tree that you see on ` <&YOCTO_GIT_URL;>`__ is
+      generated through repeating the above steps for all valid BSPs.
+      The end result is a branched, clean history tree that makes up the
+      kernel for a given release. You can see the script (``kgit-scc``)
+      responsible for this in the
+      ```yocto-kernel-tools`` <&YOCTO_GIT_URL;/cgit.cgi/yocto-kernel-tools/tree/tools>`__
+      repository.
+
+   -  The steps used to construct the full kernel tree are the same
+      steps that BitBake uses when it builds a kernel image.
+
+Build Strategy
+==============
+
+Once you have cloned a Yocto Linux kernel repository and the cache
+repository (``yocto-kernel-cache``) onto your development system, you
+can consider the compilation phase of kernel development, which is
+building a kernel image. Some prerequisites exist that are validated by
+the build process before compilation starts:
+
+-  The ```SRC_URI`` <&YOCTO_DOCS_REF_URL;#var-SRC_URI>`__ points to the
+   kernel Git repository.
+
+-  A BSP build branch with Metadata exists in the ``yocto-kernel-cache``
+   repository. The branch is based on the Yocto Linux kernel version and
+   has configurations and features grouped under the
+   ``yocto-kernel-cache/bsp`` directory. For example, features and
+   configurations for the BeagleBone Board assuming a
+   ``linux-yocto_4.12`` kernel reside in the following area of the
+   ``yocto-kernel-cache`` repository: yocto-kernel-cache/bsp/beaglebone
+
+   .. note::
+
+      In the previous example, the "yocto-4.12" branch is checked out in
+      the
+      yocto-kernel-cache
+      repository.
+
+The OpenEmbedded build system makes sure these conditions exist before
+attempting compilation. Other means, however, do exist, such as as
+bootstrapping a BSP.
+
+Before building a kernel, the build process verifies the tree and
+configures the kernel by processing all of the configuration "fragments"
+specified by feature descriptions in the ``.scc`` files. As the features
+are compiled, associated kernel configuration fragments are noted and
+recorded in the series of directories in their compilation order. The
+fragments are migrated, pre-processed and passed to the Linux Kernel
+Configuration subsystem (``lkc``) as raw input in the form of a
+``.config`` file. The ``lkc`` uses its own internal dependency
+constraints to do the final processing of that information and generates
+the final ``.config`` file that is used during compilation.
+
+Using the board's architecture and other relevant values from the
+board's template, kernel compilation is started and a kernel image is
+produced.
+
+The other thing that you notice once you configure a kernel is that the
+build process generates a build tree that is separate from your kernel's
+local Git source repository tree. This build tree has a name that uses
+the following form, where ``${MACHINE}`` is the metadata name of the
+machine (BSP) and "kernel_type" is one of the Yocto Project supported
+kernel types (e.g. "standard"): linux-${MACHINE}-kernel_type-build
+
+The existing support in the ``kernel.org`` tree achieves this default
+functionality.
+
+This behavior means that all the generated files for a particular
+machine or BSP are now in the build tree directory. The files include
+the final ``.config`` file, all the ``.o`` files, the ``.a`` files, and
+so forth. Since each machine or BSP has its own separate `Build
+Directory <&YOCTO_DOCS_REF_URL;#build-directory>`__ in its own separate
+branch of the Git repository, you can easily switch between different
+builds.