doc: Replace DocBook with sphinx-based docs

The Linux kernel moved to sphinx-based documentation and got rid of the
DocBook based documentation quite a while ago. Hence, the DocBook
documentation for U-Boot should be converted as well.

To achieve this, import the necessary files from Linux v4.17, and
convert the current DocBook documentation (three files altogether) to
sphinx/reStructuredText.

For now, all old DocBook documentation was merged into a single
handbook, tentatively named "U-Boot Hacker Manual".

For some source files, the documentation style was changed to comply
with kernel-doc; no functional changes were applied.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
diff --git a/Documentation/sphinx/cdomain.py b/Documentation/sphinx/cdomain.py
new file mode 100644
index 0000000..cf13ff3
--- /dev/null
+++ b/Documentation/sphinx/cdomain.py
@@ -0,0 +1,165 @@
+# -*- coding: utf-8; mode: python -*-
+# pylint: disable=W0141,C0113,C0103,C0325
+u"""
+    cdomain
+    ~~~~~~~
+
+    Replacement for the sphinx c-domain.
+
+    :copyright:  Copyright (C) 2016  Markus Heiser
+    :license:    GPL Version 2, June 1991 see Linux/COPYING for details.
+
+    List of customizations:
+
+    * Moved the *duplicate C object description* warnings for function
+      declarations in the nitpicky mode. See Sphinx documentation for
+      the config values for ``nitpick`` and ``nitpick_ignore``.
+
+    * Add option 'name' to the "c:function:" directive.  With option 'name' the
+      ref-name of a function can be modified. E.g.::
+
+          .. c:function:: int ioctl( int fd, int request )
+             :name: VIDIOC_LOG_STATUS
+
+      The func-name (e.g. ioctl) remains in the output but the ref-name changed
+      from 'ioctl' to 'VIDIOC_LOG_STATUS'. The function is referenced by::
+
+          * :c:func:`VIDIOC_LOG_STATUS` or
+          * :any:`VIDIOC_LOG_STATUS` (``:any:`` needs sphinx 1.3)
+
+     * Handle signatures of function-like macros well. Don't try to deduce
+       arguments types of function-like macros.
+
+"""
+
+from docutils import nodes
+from docutils.parsers.rst import directives
+
+import sphinx
+from sphinx import addnodes
+from sphinx.domains.c import c_funcptr_sig_re, c_sig_re
+from sphinx.domains.c import CObject as Base_CObject
+from sphinx.domains.c import CDomain as Base_CDomain
+
+__version__  = '1.0'
+
+# Get Sphinx version
+major, minor, patch = sphinx.version_info[:3]
+
+def setup(app):
+
+    app.override_domain(CDomain)
+
+    return dict(
+        version = __version__,
+        parallel_read_safe = True,
+        parallel_write_safe = True
+    )
+
+class CObject(Base_CObject):
+
+    """
+    Description of a C language object.
+    """
+    option_spec = {
+        "name" : directives.unchanged
+    }
+
+    def handle_func_like_macro(self, sig, signode):
+        u"""Handles signatures of function-like macros.
+
+        If the objtype is 'function' and the the signature ``sig`` is a
+        function-like macro, the name of the macro is returned. Otherwise
+        ``False`` is returned.  """
+
+        if not self.objtype == 'function':
+            return False
+
+        m = c_funcptr_sig_re.match(sig)
+        if m is None:
+            m = c_sig_re.match(sig)
+            if m is None:
+                raise ValueError('no match')
+
+        rettype, fullname, arglist, _const = m.groups()
+        arglist = arglist.strip()
+        if rettype or not arglist:
+            return False
+
+        arglist = arglist.replace('`', '').replace('\\ ', '') # remove markup
+        arglist = [a.strip() for a in arglist.split(",")]
+
+        # has the first argument a type?
+        if len(arglist[0].split(" ")) > 1:
+            return False
+
+        # This is a function-like macro, it's arguments are typeless!
+        signode  += addnodes.desc_name(fullname, fullname)
+        paramlist = addnodes.desc_parameterlist()
+        signode  += paramlist
+
+        for argname in arglist:
+            param = addnodes.desc_parameter('', '', noemph=True)
+            # separate by non-breaking space in the output
+            param += nodes.emphasis(argname, argname)
+            paramlist += param
+
+        return fullname
+
+    def handle_signature(self, sig, signode):
+        """Transform a C signature into RST nodes."""
+
+        fullname = self.handle_func_like_macro(sig, signode)
+        if not fullname:
+            fullname = super(CObject, self).handle_signature(sig, signode)
+
+        if "name" in self.options:
+            if self.objtype == 'function':
+                fullname = self.options["name"]
+            else:
+                # FIXME: handle :name: value of other declaration types?
+                pass
+        return fullname
+
+    def add_target_and_index(self, name, sig, signode):
+        # for C API items we add a prefix since names are usually not qualified
+        # by a module name and so easily clash with e.g. section titles
+        targetname = 'c.' + name
+        if targetname not in self.state.document.ids:
+            signode['names'].append(targetname)
+            signode['ids'].append(targetname)
+            signode['first'] = (not self.names)
+            self.state.document.note_explicit_target(signode)
+            inv = self.env.domaindata['c']['objects']
+            if (name in inv and self.env.config.nitpicky):
+                if self.objtype == 'function':
+                    if ('c:func', name) not in self.env.config.nitpick_ignore:
+                        self.state_machine.reporter.warning(
+                            'duplicate C object description of %s, ' % name +
+                            'other instance in ' + self.env.doc2path(inv[name][0]),
+                            line=self.lineno)
+            inv[name] = (self.env.docname, self.objtype)
+
+        indextext = self.get_index_text(name)
+        if indextext:
+            if major == 1 and minor < 4:
+                # indexnode's tuple changed in 1.4
+                # https://github.com/sphinx-doc/sphinx/commit/e6a5a3a92e938fcd75866b4227db9e0524d58f7c
+                self.indexnode['entries'].append(
+                    ('single', indextext, targetname, ''))
+            else:
+                self.indexnode['entries'].append(
+                    ('single', indextext, targetname, '', None))
+
+class CDomain(Base_CDomain):
+
+    """C language domain."""
+    name = 'c'
+    label = 'C'
+    directives = {
+        'function': CObject,
+        'member':   CObject,
+        'macro':    CObject,
+        'type':     CObject,
+        'var':      CObject,
+    }