github: Add a GitHub action to run checkpatch upon pull request

Add a new GitHub Actions workflow, checkpatch_pull.yml, which runs
checkpatch.pl for each commit in a pull request targeting the master
branch.

This change ensures proper checkpatch validation for both push
and pull request events.

.github/workflows/checkpatch_pull.yml

@@ -0,0 +1,47 @@
+name: Checkpatch upon pull
+
+on:
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  checkpatch:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+        with:
+          ref: ${{github.event.pull_request.head.sha}}
+          fetch-depth: 0
+
+      - name: Download checkpatch.pl
+        run: |
+          curl https://raw.githubusercontent.com/torvalds/linux/master/scripts/checkpatch.pl -o checkpatch.pl
+          curl https://raw.githubusercontent.com/torvalds/linux/master/scripts/spelling.txt -o spelling.txt
+          curl https://raw.githubusercontent.com/torvalds/linux/master/scripts/const_structs.checkpatch -o const_structs.checkpatch
+          chmod +x checkpatch.pl
+
+      - name: Run checkpatch.pl
+        run: |
+          ignore=(
+            MISSING_SIGN_OFF
+            EMAIL_SUBJECT
+            UNKNOWN_COMMIT_ID
+            NO_AUTHOR_SIGN_OFF
+            FILE_PATH_CHANGES
+            SPDX_LICENSE_TAG
+            LINUX_VERSION_CODE
+            CONSTANT_COMPARISON
+            SPACING
+          )
+          ignore_str=${ignore[*]}
+
+          base_commit=${{github.event.pull_request.base.sha}}
+          commits=$(git log --pretty=format:"%h" $base_commit..HEAD)
+
+          for commit in $commits; do
+            echo "Running checkpatch.pl for commit $commit"
+            git format-patch -1 --stdout $commit | ./checkpatch.pl --no-tree --show-types --ignore="${ignore_str// /,}" -
+            echo
+          done