diff --git a/Doxyfile.codec.in b/Doxyfile.codec.in
index 037ef7a..307e3e1 100644
--- a/Doxyfile.codec.in
+++ b/Doxyfile.codec.in
@@ -1485,7 +1485,7 @@
 # If a tag file is not located in the directory in which doxygen
 # is run, you must also specify the path to the tagfile here.
 
-TAGFILES               = doc/libosmocore.tag=../../core/html
+TAGFILES = doc/libosmocore.tag=../../core/html doc/libosmogsm.tag=../../gsm/html doc/libosmovty.tag=../../vty/html doc/libosmocoding.tag=../../coding/html doc/libosmoctrl.tag=../../ctrl/html doc/libosmogb.tag=../../gb/html
 
 # When a file name is specified after GENERATE_TAGFILE, doxygen will create
 # a tag file that is based on the input files it reads.
diff --git a/Doxyfile.coding.in b/Doxyfile.coding.in
index 43c4f82..d0e9942 100644
--- a/Doxyfile.coding.in
+++ b/Doxyfile.coding.in
@@ -1485,7 +1485,7 @@
 # If a tag file is not located in the directory in which doxygen
 # is run, you must also specify the path to the tagfile here.
 
-TAGFILES               = doc/libosmocore.tag=../../core/html
+TAGFILES = doc/libosmocore.tag=../../core/html doc/libosmogsm.tag=../../gsm/html doc/libosmovty.tag=../../vty/html doc/libosmocodec.tag=../../codec/html doc/libosmoctrl.tag=../../ctrl/html doc/libosmogb.tag=../../gb/html
 
 # When a file name is specified after GENERATE_TAGFILE, doxygen will create
 # a tag file that is based on the input files it reads.
diff --git a/Doxyfile.core.in b/Doxyfile.core.in
index 7a3cce5..f83205a 100644
--- a/Doxyfile.core.in
+++ b/Doxyfile.core.in
@@ -1485,7 +1485,7 @@
 # If a tag file is not located in the directory in which doxygen
 # is run, you must also specify the path to the tagfile here.
 
-TAGFILES               =
+TAGFILES = doc/libosmogsm.tag=../../gsm/html doc/libosmovty.tag=../../vty/html doc/libosmocodec.tag=../../codec/html doc/libosmocoding.tag=../../coding/html doc/libosmoctrl.tag=../../ctrl/html doc/libosmogb.tag=../../gb/html
 
 # When a file name is specified after GENERATE_TAGFILE, doxygen will create
 # a tag file that is based on the input files it reads.
diff --git a/Doxyfile.ctrl.in b/Doxyfile.ctrl.in
index eb363bb..5612a74 100644
--- a/Doxyfile.ctrl.in
+++ b/Doxyfile.ctrl.in
@@ -1485,7 +1485,7 @@
 # If a tag file is not located in the directory in which doxygen
 # is run, you must also specify the path to the tagfile here.
 
-TAGFILES               = doc/libosmocore.tag=../../core/html
+TAGFILES = doc/libosmocore.tag=../../core/html doc/libosmogsm.tag=../../gsm/html doc/libosmovty.tag=../../vty/html doc/libosmocodec.tag=../../codec/html doc/libosmocoding.tag=../../coding/html doc/libosmogb.tag=../../gb/html
 
 # When a file name is specified after GENERATE_TAGFILE, doxygen will create
 # a tag file that is based on the input files it reads.
diff --git a/Doxyfile.gb.in b/Doxyfile.gb.in
index e6b7826..b3b2128 100644
--- a/Doxyfile.gb.in
+++ b/Doxyfile.gb.in
@@ -1485,7 +1485,7 @@
 # If a tag file is not located in the directory in which doxygen
 # is run, you must also specify the path to the tagfile here.
 
-TAGFILES               = doc/libosmocore.tag=../../core/html
+TAGFILES = doc/libosmocore.tag=../../core/html doc/libosmogsm.tag=../../gsm/html doc/libosmovty.tag=../../vty/html doc/libosmocodec.tag=../../codec/html doc/libosmocoding.tag=../../coding/html doc/libosmoctrl.tag=../../ctrl/html
 
 # When a file name is specified after GENERATE_TAGFILE, doxygen will create
 # a tag file that is based on the input files it reads.
diff --git a/Doxyfile.gsm.in b/Doxyfile.gsm.in
index 27d14cc..aae0e89 100644
--- a/Doxyfile.gsm.in
+++ b/Doxyfile.gsm.in
@@ -1485,7 +1485,7 @@
 # If a tag file is not located in the directory in which doxygen
 # is run, you must also specify the path to the tagfile here.
 
-TAGFILES               = doc/libosmocore.tag=../../core/html
+TAGFILES = doc/libosmocore.tag=../../core/html doc/libosmovty.tag=../../vty/html doc/libosmocodec.tag=../../codec/html doc/libosmocoding.tag=../../coding/html doc/libosmoctrl.tag=../../ctrl/html doc/libosmogb.tag=../../gb/html
 
 # When a file name is specified after GENERATE_TAGFILE, doxygen will create
 # a tag file that is based on the input files it reads.
diff --git a/Doxyfile.vty.in b/Doxyfile.vty.in
index 0e138ee..fb1cabf 100644
--- a/Doxyfile.vty.in
+++ b/Doxyfile.vty.in
@@ -1485,7 +1485,7 @@
 # If a tag file is not located in the directory in which doxygen
 # is run, you must also specify the path to the tagfile here.
 
-TAGFILES               = doc/libosmocore.tag=../../core/html
+TAGFILES = doc/libosmocore.tag=../../core/html doc/libosmogsm.tag=../../gsm/html doc/libosmocodec.tag=../../codec/html doc/libosmocoding.tag=../../coding/html doc/libosmoctrl.tag=../../ctrl/html doc/libosmogb.tag=../../gb/html
 
 # When a file name is specified after GENERATE_TAGFILE, doxygen will create
 # a tag file that is based on the input files it reads.
diff --git a/Makefile.am b/Makefile.am
index de5eb35..9e0888f 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -39,38 +39,140 @@
 		  $(top_builddir)/doc/gb/html/index.html
 	cd $(top_builddir)/doc && tar cf html.tar */html
 
-$(top_builddir)/doc/core/html/index.html: $(SOURCES) Doxyfile.core
-	@rm -rf doc/core
-	mkdir -p doc/core
+# Support doxygen cross references from each library to each other library:
+# First generate the docs to make sure all .tag files are in place.
+# In a second run, generate the content with proper referencing.
+# For example, libosmocore references tags from libosmovty and vice versa,
+# so both need to generate tag files first, and then do another run.
+#
+# Generate each docs tree, and touch a libosmofoo.tag.prep file when done.
+# It means that a libosmofoo.tag file is up-to-date.
+# Touch a separate "*.prep" target: libosmofoo.tag as target would create
+# circular dependency: we would rebuild all every time 'make' is invoked.
+# The .prep file also depends on all the source files for that library.
+
+$(top_builddir)/doc/libosmocore.tag.prep: $(top_builddir)/Doxyfile.core
+	rm -rf $(top_builddir)/doc/core; mkdir -p $(top_builddir)/doc/core
+	rm -rf $(top_builddir)/doc/libosmocore.map
+	-$(DOXYGEN) $(top_builddir)/Doxyfile.core
+	touch "$@"
+
+$(top_builddir)/doc/libosmogsm.tag.prep: $(top_builddir)/Doxyfile.gsm
+	rm -rf $(top_builddir)/doc/gsm; mkdir -p $(top_builddir)/doc/gsm
+	rm -rf $(top_builddir)/doc/libosmogsm.map
+	-$(DOXYGEN) $(top_builddir)/Doxyfile.gsm
+	touch "$@"
+
+$(top_builddir)/doc/libosmovty.tag.prep: $(top_builddir)/Doxyfile.vty
+	rm -rf $(top_builddir)/doc/vty; mkdir -p $(top_builddir)/doc/vty
+	rm -rf $(top_builddir)/doc/libosmovty.map
+	-$(DOXYGEN) $(top_builddir)/Doxyfile.vty
+	touch "$@"
+
+$(top_builddir)/doc/libosmocodec.tag.prep: $(top_builddir)/Doxyfile.codec
+	rm -rf $(top_builddir)/doc/codec; mkdir -p $(top_builddir)/doc/codec
+	rm -rf $(top_builddir)/doc/libosmocodec.map
+	-$(DOXYGEN) $(top_builddir)/Doxyfile.codec
+	touch "$@"
+
+$(top_builddir)/doc/libosmocoding.tag.prep: $(top_builddir)/Doxyfile.coding
+	rm -rf $(top_builddir)/doc/coding; mkdir -p $(top_builddir)/doc/coding
+	rm -rf $(top_builddir)/doc/libosmocoding.map
+	-$(DOXYGEN) $(top_builddir)/Doxyfile.coding
+	touch "$@"
+
+$(top_builddir)/doc/libosmoctrl.tag.prep: $(top_builddir)/Doxyfile.ctrl
+	rm -rf $(top_builddir)/doc/ctrl; mkdir -p $(top_builddir)/doc/ctrl
+	rm -rf $(top_builddir)/doc/libosmoctrl.map
+	-$(DOXYGEN) $(top_builddir)/Doxyfile.ctrl
+	touch "$@"
+
+$(top_builddir)/doc/libosmogb.tag.prep: $(top_builddir)/Doxyfile.gb
+	rm -rf $(top_builddir)/doc/gb; mkdir -p $(top_builddir)/doc/gb
+	rm -rf $(top_builddir)/doc/libosmogb.map
+	-$(DOXYGEN) $(top_builddir)/Doxyfile.gb
+	touch "$@"
+
+# Build for real once all depending .tag files are in place.
+# Depend on the own .tag.prep file to avoid concurrent builds of the same doc
+# tree, and to also depend on all the source files listed above.
+#
+# Each library should depend on all the tag.prep files of which it lists .tag
+# files in Doxyfile under TAGFILES.
+#
+# In turn, include all .tag files in TAGFILES of libraries to which "\ref"
+# references point.
+#
+# Easiest is to just depend on all tag.prep files all across everywhere.
+
+$(top_builddir)/doc/core/html/index.html: $(top_builddir)/doc/libosmocore.tag.prep \
+		$(top_builddir)/doc/libosmogsm.tag.prep \
+		$(top_builddir)/doc/libosmovty.tag.prep \
+		$(top_builddir)/doc/libosmocodec.tag.prep \
+		$(top_builddir)/doc/libosmocoding.tag.prep \
+		$(top_builddir)/doc/libosmoctrl.tag.prep \
+		$(top_builddir)/doc/libosmogb.tag.prep
+	rm -rf $(top_builddir)/doc/core; mkdir -p $(top_builddir)/doc/core
 	$(DOXYGEN) Doxyfile.core
 
-$(top_builddir)/doc/gsm/html/index.html: $(SOURCES) Doxyfile.gsm
-	@rm -rf doc/gsm
-	mkdir -p doc/gsm
+$(top_builddir)/doc/gsm/html/index.html: $(top_builddir)/doc/libosmogsm.tag.prep \
+		$(top_builddir)/doc/libosmocore.tag.prep \
+		$(top_builddir)/doc/libosmovty.tag.prep \
+		$(top_builddir)/doc/libosmocodec.tag.prep \
+		$(top_builddir)/doc/libosmocoding.tag.prep \
+		$(top_builddir)/doc/libosmoctrl.tag.prep \
+		$(top_builddir)/doc/libosmogb.tag.prep
+	rm -rf $(top_builddir)/doc/gsm; mkdir -p $(top_builddir)/doc/gsm
 	$(DOXYGEN) Doxyfile.gsm
 
-$(top_builddir)/doc/vty/html/index.html: $(SOURCES) Doxyfile.vty
-	@rm -rf doc/vty/{html,latex}
+$(top_builddir)/doc/vty/html/index.html: $(top_builddir)/doc/libosmovty.tag.prep \
+		$(top_builddir)/doc/libosmocore.tag.prep \
+		$(top_builddir)/doc/libosmogsm.tag.prep \
+		$(top_builddir)/doc/libosmocodec.tag.prep \
+		$(top_builddir)/doc/libosmocoding.tag.prep \
+		$(top_builddir)/doc/libosmoctrl.tag.prep \
+		$(top_builddir)/doc/libosmogb.tag.prep
+	rm -rf $(top_builddir)/doc/vty; mkdir -p $(top_builddir)/doc/vty
 	$(DOXYGEN) Doxyfile.vty
 
-$(top_builddir)/doc/codec/html/index.html: $(SOURCES) Doxyfile.codec
-	@rm -rf doc/codec
-	mkdir -p doc/codec
+$(top_builddir)/doc/codec/html/index.html: $(top_builddir)/doc/libosmocodec.tag.prep \
+		$(top_builddir)/doc/libosmocore.tag.prep \
+		$(top_builddir)/doc/libosmogsm.tag.prep \
+		$(top_builddir)/doc/libosmovty.tag.prep \
+		$(top_builddir)/doc/libosmocoding.tag.prep \
+		$(top_builddir)/doc/libosmoctrl.tag.prep \
+		$(top_builddir)/doc/libosmogb.tag.prep
+	rm -rf $(top_builddir)/doc/codec; mkdir -p $(top_builddir)/doc/codec
 	$(DOXYGEN) Doxyfile.codec
 
-$(top_builddir)/doc/coding/html/index.html: Doxyfile.coding
-	@rm -rf doc/coding
-	mkdir -p doc/coding
+$(top_builddir)/doc/coding/html/index.html: $(top_builddir)/doc/libosmocoding.tag.prep \
+		$(top_builddir)/doc/libosmocore.tag.prep \
+		$(top_builddir)/doc/libosmogsm.tag.prep \
+		$(top_builddir)/doc/libosmovty.tag.prep \
+		$(top_builddir)/doc/libosmocodec.tag.prep \
+		$(top_builddir)/doc/libosmoctrl.tag.prep \
+		$(top_builddir)/doc/libosmogb.tag.prep
+	rm -rf $(top_builddir)/doc/coding; mkdir -p $(top_builddir)/doc/coding
 	$(DOXYGEN) Doxyfile.coding
 
-$(top_builddir)/doc/ctrl/html/index.html: $(SOURCES) Doxyfile.ctrl
-	@rm -rf doc/ctrl
-	mkdir -p doc/ctrl
+$(top_builddir)/doc/ctrl/html/index.html: $(top_builddir)/doc/libosmoctrl.tag.prep \
+		$(top_builddir)/doc/libosmocore.tag.prep \
+		$(top_builddir)/doc/libosmogsm.tag.prep \
+		$(top_builddir)/doc/libosmovty.tag.prep \
+		$(top_builddir)/doc/libosmocodec.tag.prep \
+		$(top_builddir)/doc/libosmocoding.tag.prep \
+		$(top_builddir)/doc/libosmogb.tag.prep
+	rm -rf $(top_builddir)/doc/ctrl; mkdir -p $(top_builddir)/doc/ctrl
 	$(DOXYGEN) Doxyfile.ctrl
 
-$(top_builddir)/doc/gb/html/index.html: $(SOURCES) Doxyfile.gb
-	@rm -rf doc/gb
-	mkdir -p doc/gb
+$(top_builddir)/doc/gb/html/index.html: $(top_builddir)/doc/libosmogb.tag.prep \
+		$(top_builddir)/doc/libosmocore.tag.prep \
+		$(top_builddir)/doc/libosmogsm.tag.prep \
+		$(top_builddir)/doc/libosmovty.tag.prep \
+		$(top_builddir)/doc/libosmocodec.tag.prep \
+		$(top_builddir)/doc/libosmocoding.tag.prep \
+		$(top_builddir)/doc/libosmoctrl.tag.prep
+	rm -rf $(top_builddir)/doc/gb; mkdir -p $(top_builddir)/doc/gb
 	$(DOXYGEN) Doxyfile.gb
 
 install-data-hook:
@@ -79,7 +181,7 @@
 uninstall-hook:
 	cd $(DESTDIR)$(htmldir) && rm -rf {core,gsm,vty,codec,coding,ctrl,gb}
 
-DX_CLEAN = doc/{core,gsm,vty,codec,coding,ctrl,gb}/html/search/* doc/{core,gsm,vty,codec,coding,ctrl,gb}/{html,latex}/* doc/html.tar doc/{core,gsm,vty,codec,coding,ctrl,gb}/doxygen_sqlite3.db doc/*.tag
+DX_CLEAN = doc/{core,gsm,vty,codec,coding,ctrl,gb}/html/search/* doc/{core,gsm,vty,codec,coding,ctrl,gb}/{html,latex}/* doc/html.tar doc/{core,gsm,vty,codec,coding,ctrl,gb}/doxygen_sqlite3.db doc/*.tag doc/*.tag.prep
 endif
 
 MOSTLYCLEANFILES = $(DX_CLEAN)