doc: update Kernel documentation build system

Update the documentation build system according to Linux v5.11-rc1.

Deactive the automarkup.py extension module which on Gitlab CI is
incompatible with Unicode.

With this patch we can build the HTML documentation using either of
Sphinx 2 and Sphinx 3.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/doc/sphinx/kernel_abi.py b/doc/sphinx/kernel_abi.py
new file mode 100644
index 0000000..f3da859
--- /dev/null
+++ b/doc/sphinx/kernel_abi.py
@@ -0,0 +1,194 @@
+# -*- coding: utf-8; mode: python -*-
+# coding=utf-8
+# SPDX-License-Identifier: GPL-2.0
+#
+u"""
+    kernel-abi
+    ~~~~~~~~~~
+
+    Implementation of the ``kernel-abi`` reST-directive.
+
+    :copyright:  Copyright (C) 2016  Markus Heiser
+    :copyright:  Copyright (C) 2016-2020  Mauro Carvalho Chehab
+    :maintained-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
+    :license:    GPL Version 2, June 1991 see Linux/COPYING for details.
+
+    The ``kernel-abi`` (:py:class:`KernelCmd`) directive calls the
+    scripts/get_abi.pl script to parse the Kernel ABI files.
+
+    Overview of directive's argument and options.
+
+    .. code-block:: rst
+
+        .. kernel-abi:: <ABI directory location>
+            :debug:
+
+    The argument ``<ABI directory location>`` is required. It contains the
+    location of the ABI files to be parsed.
+
+    ``debug``
+      Inserts a code-block with the *raw* reST. Sometimes it is helpful to see
+      what reST is generated.
+
+"""
+
+import codecs
+import os
+import subprocess
+import sys
+import re
+import kernellog
+
+from os import path
+
+from docutils import nodes, statemachine
+from docutils.statemachine import ViewList
+from docutils.parsers.rst import directives, Directive
+from docutils.utils.error_reporting import ErrorString
+
+#
+# AutodocReporter is only good up to Sphinx 1.7
+#
+import sphinx
+
+Use_SSI = sphinx.__version__[:3] >= '1.7'
+if Use_SSI:
+    from sphinx.util.docutils import switch_source_input
+else:
+    from sphinx.ext.autodoc import AutodocReporter
+
+__version__  = '1.0'
+
+def setup(app):
+
+    app.add_directive("kernel-abi", KernelCmd)
+    return dict(
+        version = __version__
+        , parallel_read_safe = True
+        , parallel_write_safe = True
+    )
+
+class KernelCmd(Directive):
+
+    u"""KernelABI (``kernel-abi``) directive"""
+
+    required_arguments = 1
+    optional_arguments = 2
+    has_content = False
+    final_argument_whitespace = True
+
+    option_spec = {
+        "debug"     : directives.flag,
+        "rst"       : directives.unchanged
+    }
+
+    def run(self):
+
+        doc = self.state.document
+        if not doc.settings.file_insertion_enabled:
+            raise self.warning("docutils: file insertion disabled")
+
+        env = doc.settings.env
+        cwd = path.dirname(doc.current_source)
+        cmd = "get_abi.pl rest --enable-lineno --dir "
+        cmd += self.arguments[0]
+
+        if 'rst' in self.options:
+            cmd += " --rst-source"
+
+        srctree = path.abspath(os.environ["srctree"])
+
+        fname = cmd
+
+        # extend PATH with $(srctree)/scripts
+        path_env = os.pathsep.join([
+            srctree + os.sep + "scripts",
+            os.environ["PATH"]
+        ])
+        shell_env = os.environ.copy()
+        shell_env["PATH"]    = path_env
+        shell_env["srctree"] = srctree
+
+        lines = self.runCmd(cmd, shell=True, cwd=cwd, env=shell_env)
+        nodeList = self.nestedParse(lines, self.arguments[0])
+        return nodeList
+
+    def runCmd(self, cmd, **kwargs):
+        u"""Run command ``cmd`` and return it's stdout as unicode."""
+
+        try:
+            proc = subprocess.Popen(
+                cmd
+                , stdout = subprocess.PIPE
+                , stderr = subprocess.PIPE
+                , **kwargs
+            )
+            out, err = proc.communicate()
+
+            out, err = codecs.decode(out, 'utf-8'), codecs.decode(err, 'utf-8')
+
+            if proc.returncode != 0:
+                raise self.severe(
+                    u"command '%s' failed with return code %d"
+                    % (cmd, proc.returncode)
+                )
+        except OSError as exc:
+            raise self.severe(u"problems with '%s' directive: %s."
+                              % (self.name, ErrorString(exc)))
+        return out
+
+    def nestedParse(self, lines, fname):
+        content = ViewList()
+        node = nodes.section()
+
+        if "debug" in self.options:
+            code_block = "\n\n.. code-block:: rst\n    :linenos:\n"
+            for l in lines.split("\n"):
+                code_block += "\n    " + l
+            lines = code_block + "\n\n"
+
+        line_regex = re.compile("^#define LINENO (\S+)\#([0-9]+)$")
+        ln = 0
+        n = 0
+        f = fname
+
+        for line in lines.split("\n"):
+            n = n + 1
+            match = line_regex.search(line)
+            if match:
+                new_f = match.group(1)
+
+                # Sphinx parser is lazy: it stops parsing contents in the
+                # middle, if it is too big. So, handle it per input file
+                if new_f != f and content:
+                    self.do_parse(content, node)
+                    content = ViewList()
+
+                f = new_f
+
+                # sphinx counts lines from 0
+                ln = int(match.group(2)) - 1
+            else:
+                content.append(line, f, ln)
+
+        kernellog.info(self.state.document.settings.env.app, "%s: parsed %i lines" % (fname, n))
+
+        if content:
+            self.do_parse(content, node)
+
+        return node.children
+
+    def do_parse(self, content, node):
+        if Use_SSI:
+            with switch_source_input(self.state, content):
+                self.state.nested_parse(content, 0, node, match_titles=1)
+        else:
+            buf  = self.state.memo.title_styles, self.state.memo.section_level, self.state.memo.reporter
+
+            self.state.memo.title_styles  = []
+            self.state.memo.section_level = 0
+            self.state.memo.reporter      = AutodocReporter(content, self.state.memo.reporter)
+            try:
+                self.state.nested_parse(content, 0, node, match_titles=1)
+            finally:
+                self.state.memo.title_styles, self.state.memo.section_level, self.state.memo.reporter = buf