device: Add device subsystem enumeration script

The device enumeration feature requires all devices
to place their API implementation in linker sections
by api type. This commit adds a script which uses
the tag __subsystem to identify all existing driver
API types and generate iterable sections for them.

The script is invoked from the top CMakeLists.txt

Signed-off-by: Bjarki Arge Andreasen <baa@trackunit.com>
Co-authored-by: Pieter De Gendt <pieter.degendt@basalte.be>
Signed-off-by: Pieter De Gendt <pieter.degendt@basalte.be>

CMakeLists.txt

@@ -88,6 +88,7 @@ set(SYSCALL_LIST_H_TARGET      syscall_list_h_target)
 set(DRIVER_VALIDATION_H_TARGET driver_validation_h_target)
 set(KOBJ_TYPES_H_TARGET        kobj_types_h_target)
 set(PARSE_SYSCALLS_TARGET      parse_syscalls_target)
+set(DEVICE_API_LD_TARGET       device_api_ld_target)
 
 define_property(GLOBAL PROPERTY PROPERTY_OUTPUT_FORMAT BRIEF_DOCS " " FULL_DOCS " ")
 set_property(   GLOBAL PROPERTY PROPERTY_OUTPUT_FORMAT elf32-little${ARCH}) # BFD format
@@ -882,6 +883,28 @@ add_custom_target(${DRIVER_VALIDATION_H_TARGET} DEPENDS ${DRV_VALIDATION})
 include(${ZEPHYR_BASE}/cmake/kobj.cmake)
 gen_kobj(KOBJ_INCLUDE_PATH)
 
+# Generate sections for kernel device subsystems
+set(
+  DEVICE_API_LD_SECTIONS
+  ${CMAKE_CURRENT_BINARY_DIR}/include/generated/device-api-sections.ld
+  )
+
+add_custom_command(
+  OUTPUT ${DEVICE_API_LD_SECTIONS}
+  COMMAND
+    ${PYTHON_EXECUTABLE}
+    ${ZEPHYR_BASE}/scripts/build/gen_iter_sections.py
+    --input ${struct_tags_json}
+    --tag __subsystem
+    --ld-output ${DEVICE_API_LD_SECTIONS}
+  DEPENDS
+    ${ZEPHYR_BASE}/scripts/build/gen_iter_sections.py
+    ${struct_tags_json}
+  WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+  )
+
+add_custom_target(${DEVICE_API_LD_TARGET} DEPENDS ${DEVICE_API_LD_SECTIONS})
+
 # Add a pseudo-target that is up-to-date when all generated headers
 # are up-to-date.
 
@@ -912,6 +935,7 @@ add_dependencies(zephyr_interface
   ${SYSCALL_LIST_H_TARGET}
   ${DRIVER_VALIDATION_H_TARGET}
   ${KOBJ_TYPES_H_TARGET}
+  ${DEVICE_API_LD_TARGET}
   )
 
 add_custom_command(

include/zephyr/linker/common-rom/common-rom-kernel-devices.ld

@@ -102,3 +102,5 @@
 #include <zephyr/linker/device-deps.ld>
 	} GROUP_ROM_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
 #endif /* !CONFIG_DEVICE_DEPS_DYNAMIC */
+
+#include <device-api-sections.ld>

scripts/build/gen_iter_sections.py

@@ -0,0 +1,48 @@
+#!/usr/bin/env python3
+#
+# Copyright (c) 2023 Bjarki Arge Andreasen
+#
+# SPDX-License-Identifier: Apache-2.0
+"""
+Script to generate iterable sections from JSON encoded dictionary containing lists of items.
+"""
+
+import argparse
+import json
+
+
+def get_tagged_items(filepath: str, tag: str) -> list:
+    with open(filepath) as fp:
+        return json.load(fp)[tag]
+
+
+def gen_ld(filepath: str, items: list):
+    with open(filepath, "w") as fp:
+        for item in items:
+            fp.write(f"ITERABLE_SECTION_ROM({item}, Z_LINK_ITERABLE_SUBALIGN)\n")
+
+
+def parse_args() -> argparse.Namespace:
+    parser = argparse.ArgumentParser(
+        description=__doc__,
+        formatter_class=argparse.RawDescriptionHelpFormatter,
+        allow_abbrev=False,
+    )
+
+    parser.add_argument("-i", "--input", required=True, help="Path to input list of tags")
+    parser.add_argument("-t", "--tag", required=True, help="Tag to generate iterable sections for")
+    parser.add_argument("-l", "--ld-output", required=True, help="Path to output linker file")
+
+    return parser.parse_args()
+
+
+def main():
+    args = parse_args()
+
+    items = get_tagged_items(args.input, args.tag)
+
+    gen_ld(args.ld_output, items)
+
+
+if __name__ == "__main__":
+    main()