scripts: gen_handles: output dependency graph

Output the final dependency graph as a `.dot` file, which when rendered
by graphviz can be easier to comprehend than the text descriptions.

This output is optional in that it will not be generated if `graphviz`
is not installed.

Signed-off-by: Jordan Yates <jordan.yates@data61.csiro.au>

CMakeLists.txt

@@ -872,6 +872,7 @@ if(CONFIG_HAS_DTS)
     ${PYTHON_EXECUTABLE}
     ${ZEPHYR_BASE}/scripts/build/gen_handles.py
     --output-source dev_handles.c
+    --output-graphviz dev_graph.dot
     --num-dynamic-devices ${number_of_dynamic_devices}
     --kernel $<TARGET_FILE:${ZEPHYR_LINK_STAGE_EXECUTABLE}>
     --zephyr-base ${ZEPHYR_BASE}

scripts/build/elf_parser.py

@@ -254,3 +254,25 @@ class ZephyrElf:
 
         # Link injected devices to each other
         self._link_injected(devices_by_ord)
+
+    def device_dependency_graph(self, title, comment):
+        """
+        Construct a graphviz Digraph of the relationships between devices.
+        """
+        import graphviz
+        dot = graphviz.Digraph(title, comment=comment)
+        # Split iteration so nodes and edges are grouped in source
+        for dev in self.devices:
+            if dev.ordinal == DeviceOrdinals.DEVICE_HANDLE_NULL:
+                text = '{:s}\\nHandle: {:d}'.format(dev.sym.name, dev.handle)
+            else:
+                n = self.edt.dep_ord2node[dev.ordinal]
+                label = n.labels[0] if n.labels else n.label
+                text = '{:s}\\nOrdinal: {:d} | Handle: {:d}\\n{:s}'.format(
+                    label, dev.ordinal, dev.handle, n.path
+                )
+            dot.node(str(dev.ordinal), text)
+        for dev in self.devices:
+            for sup in dev.devs_supports:
+                dot.edge(str(dev.ordinal), str(sup.ordinal))
+        return dot

scripts/build/gen_handles.py

@@ -51,6 +51,8 @@ def parse_args():
                         type=int, help="Input number of dynamic devices allowed")
     parser.add_argument("-o", "--output-source", required=True,
                         help="Output source file")
+    parser.add_argument("-g", "--output-graphviz",
+                        help="Output file for graphviz dependency graph")
     parser.add_argument("-z", "--zephyr-base",
                         help="Path to current Zephyr base. If this argument \
                         is not provided the environment will be checked for \
@@ -116,6 +118,15 @@ def main():
 
     parsed_elf = ZephyrElf(args.kernel, edt, args.start_symbol)
 
+    if args.output_graphviz:
+        # Try and output the dependency tree
+        try:
+            dot = parsed_elf.device_dependency_graph('Device dependency graph', args.kernel)
+            with open(args.output_graphviz, 'w') as f:
+                f.write(dot.source)
+        except ImportError:
+            pass
+
     with open(args.output_source, "w") as fp:
         fp.write('#include <zephyr/device.h>\n')
         fp.write('#include <zephyr/toolchain.h>\n')

scripts/requirements-extras.txt

@@ -26,3 +26,6 @@ grpcio-tools
 
 # used by scripts/release/bug_bash.py for generating top ten bug squashers
 PyGithub
+
+# used to generate devicetree dependency graphs
+graphviz