doc-rst: generic way to build only sphinx sub-folders

Add a generic way to build only a reST sub-folder with or
without a individual *build-theme*.

* control *sub-folders* by environment SPHINXDIRS
* control *build-theme* by environment SPHINX_CONF

Folders with a conf.py file, matching $(srctree)/Documentation/*/conf.py
can be build and distributed *stand-alone*. E.g. to compile only the
html of 'media' and 'gpu' folder use::

  make SPHINXDIRS="media gpu" htmldocs

To use an additional sphinx-build configuration (*build-theme*) set the
name of the configuration file to SPHINX_CONF. E.g. to compile only the
html of 'media' with the *nit-picking* build use::

  make SPHINXDIRS=media SPHINX_CONF=conf_nitpick.py htmldocs

With this, the Documentation/conf.py is read first and updated with the
configuration values from the Documentation/media/conf_nitpick.py.

Signed-off-by: Markus Heiser <markus.heiser@darmarIT.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 7 insertions, 0 deletions

diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile
index 64460a897f56..a91c96522379 100644
--- a/Documentation/DocBook/Makefile
+++ b/Documentation/DocBook/Makefile
@@ -22,9 +22,15 @@ ifeq ($(DOCBOOKS),)
 # Skip DocBook build if the user explicitly requested no DOCBOOKS.
 .DEFAULT:
 	@echo "  SKIP    DocBook $@ target (DOCBOOKS=\"\" specified)."
+else
+ifneq ($(SPHINXDIRS),)
 
+# Skip DocBook build if the user explicitly requested a sphinx dir
+.DEFAULT:
+	@echo "  SKIP    DocBook $@ target (SPHINXDIRS specified)."
 else
 
+
 ###
 # The build process is as follows (targets):
 #              (xmldocs) [by docproc]
@@ -221,6 +227,7 @@ silent_gen_xml = :
 	   echo "</programlisting>")  > $@
 
 endif # DOCBOOKS=""
+endif # SPHINDIR=...
 
 ###
 # Help targets as used by the top-level makefile