Documentation: switch to pdflatex for pdf generation

Looks like rst2pdf is not robust enough, especially for large documents.

Use recursive make on the Sphinx generated makefile to convert latex to
pdf. The ugly detail is that pdf is generated into
Documentation/output/latex.

Unfortunately, the pdflatex build generates huge amounts of build log
noise, and also fails in the end. We'll fix that next.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Markus Heiser <markus.heiser@darmarit.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/Makefile.sphinx

@@ -25,8 +25,8 @@ else ifneq ($(DOCBOOKS),)
 
 else # HAVE_SPHINX
 
-# User-friendly check for rst2pdf
-HAVE_RST2PDF := $(shell if python -c "import rst2pdf" >/dev/null 2>&1; then echo 1; else echo 0; fi)
+# User-friendly check for pdflatex
+HAVE_PDFLATEX := $(shell if which pdflatex >/dev/null 2>&1; then echo 1; else echo 0; fi)
 
 # Internal variables.
 PAPEROPT_a4     = -D latex_paper_size=a4
@@ -44,12 +44,13 @@ htmldocs:
 	$(call cmd,sphinx,html)
 
 pdfdocs:
-ifeq ($(HAVE_RST2PDF),0)
-	$(warning The Python 'rst2pdf' module was not found. Make sure you have the module installed to produce PDF output.)
+ifeq ($(HAVE_PDFLATEX),0)
+	$(warning The 'pdflatex' command was not found. Make sure you have it installed and in PATH to produce PDF output.)
 	@echo "  SKIP    Sphinx $@ target."
-else # HAVE_RST2PDF
-	$(call cmd,sphinx,pdf)
-endif # HAVE_RST2PDF
+else # HAVE_PDFLATEX
+	$(call cmd,sphinx,latex)
+	$(Q)$(MAKE) -C $(BUILDDIR)/latex
+endif # HAVE_PDFLATEX
 
 epubdocs:
 	$(call cmd,sphinx,epub)