buildroot: Add support for applying local patches

LoongArch support is only available as an in-review patch on the mailing
list. Add scaffolding to make it easy to apply patches on top of the
Buildroot tarball.

To make it easy to add and remove patches while ensuring they get
applied properly, keep the downloaded tarball instead of removing it
after extraction, so that the source can be cleanly recreated each run.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>

buildroot/rebuild.py

@@ -72,16 +72,17 @@ def build_image(architecture, edit_config):
 
 
 def download_and_extract_buildroot():
+    if SRC_FOLDER.exists():
+        shutil.rmtree(SRC_FOLDER)
     SRC_FOLDER.mkdir(parents=True)
 
     tarball = Path(ROOT_FOLDER, f"buildroot-{BUILDROOT_VERSION}.tar.gz")
-    tarball.unlink(missing_ok=True)
-
-    curl_cmd = [
-        'curl', '-LSs', '-o', tarball,
-        f"https://buildroot.org/downloads/{tarball.name}"
-    ]
-    subprocess.run(curl_cmd, check=True)
+    if not tarball.exists():
+        curl_cmd = [
+            'curl', '-LSs', '-o', tarball,
+            f"https://buildroot.org/downloads/{tarball.name}"
+        ]
+        subprocess.run(curl_cmd, check=True)
 
     sha256_cmd = ['sha256sum', '--quiet', '-c', f"{tarball.name}.sha256"]
     subprocess.run(sha256_cmd, check=True, cwd=ROOT_FOLDER)
@@ -91,27 +92,18 @@ def download_and_extract_buildroot():
     ]
     subprocess.run(tar_cmd, check=True)
 
-    tarball.unlink(missing_ok=True)
-
-
-def download_buildroot_if_necessary():
-    if SRC_FOLDER.exists():
-        # Make support/scripts/setlocalversion do nothing because we are in a
-        # git repository so it will return information about this repo, not
-        # Buildroot
-        setlocalversion = Path(SRC_FOLDER, 'support/scripts/setlocalversion')
-        setlocalversion.write_text('', encoding='utf-8')
-
-        installed_version = subprocess.run(['make', 'print-version'],
-                                           capture_output=True,
-                                           check=True,
-                                           cwd=SRC_FOLDER,
-                                           text=True).stdout.strip()
-        if installed_version != BUILDROOT_VERSION:
-            shutil.rmtree(SRC_FOLDER)
-            download_and_extract_buildroot()
-    else:
-        download_and_extract_buildroot()
+    if (patches := list(ROOT_FOLDER.glob('*.patch'))):
+        for patch in patches:
+            patch_cmd = [
+                'patch', '--directory', SRC_FOLDER, '--input', patch,
+                '--strip', '1'
+            ]
+            try:
+                subprocess.run(patch_cmd, check=True)
+            except subprocess.CalledProcessError as err:
+                raise RuntimeError(
+                    f"{patch} did not apply to Buildroot {BUILDROOT_VERSION}, does it need to be updated?"
+                ) from err
 
 
 def release_images():
@@ -161,7 +153,7 @@ def parse_arguments():
 
     architectures = SUPPORTED_ARCHES if 'all' in args.architectures else args.architectures
 
-    download_buildroot_if_necessary()
+    download_and_extract_buildroot()
     for arch in architectures:
         build_image(arch, args.edit_config)