github actions: Add reusable workflow for validating kernel commits

Converts the upstream-commit-check workflow (from ciqlts9_2) to a
reusable workflow that can be referenced from branches. This allows
maintaining the workflow definition in one place while using it
across many branches.

The workflow uses workflow_call trigger and accepts all necessary
context from the calling workflow via github context variables.

We are renaming the workflow and some of the labels it uses to be
more general.  In the future, more kernel commit validation will
happen in this workflow besides just the upstream fixes check

Author: bmastbergen

.github/workflows/validate-kernel-commits.yml

@@ -0,0 +1,80 @@
+name: Validate Kernel Commits
+
+on:
+  workflow_call:
+    # No inputs needed - uses github context from caller
+
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  validate-kernel-commits:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout PR branch
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          ref: ${{ github.head_ref }}
+
+      - name: Checkout base branch
+        run: |
+          git fetch origin ${{ github.base_ref }}:${{ github.base_ref }}
+
+      - name: Download check_kernel_commits.py
+        run: |
+          curl -sL \
+            https://raw.githubusercontent.com/ctrliq/kernel-src-tree-tools/mainline/check_kernel_commits.py \
+            -o check_kernel_commits.py
+          chmod +x check_kernel_commits.py
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.x'
+
+      - name: Run upstream fixes check
+        id: check-kernel-commits
+        run: |
+          set +e  # Don't exit on error, we want to capture the output
+          python3 check_kernel_commits.py --repo . --pr_branch "${{ github.head_ref }}" --base_branch "${{ github.base_ref }}" --markdown | tee result.txt
+          EXIT_CODE=$?
+
+          # Check if the script failed
+          if [ $EXIT_CODE -ne 0 ]; then
+            echo "❌ Kernel commits check failed with exit code $EXIT_CODE"
+            exit $EXIT_CODE
+          fi
+
+          # Check for findings:
+          # 1. Verify the success message exists
+          # 2. If it exists, check if there are any OTHER lines (which would indicate issues)
+          # 3. If success message doesn't exist, that's also a finding
+          if grep -q "All referenced commits exist upstream and have no Fixes: tags." result.txt; then
+            # Success message found, check if there are any other lines
+            LINE_COUNT=$(wc -l < ../ckc_result.txt)
+            if [ "$LINE_COUNT" -gt 1 ]; then
+              echo "has_findings=true" >> $GITHUB_OUTPUT
+            else
+              echo "has_findings=false" >> $GITHUB_OUTPUT
+            fi
+          else
+            # Success message not found, there must be findings
+            echo "has_findings=true" >> $GITHUB_OUTPUT
+          fi
+
+          set -e  # Re-enable exit on error
+
+      - name: Comment on PR if issues found
+        if: steps.check-kernel-commits.outputs.has_findings == 'true'
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          if ! gh pr comment ${{ github.event.pull_request.number }} \
+            --body-file result.txt \
+            --repo ${{ github.repository }}; then
+            echo "❌ Failed to post check-kernel-commits comment to PR"
+            exit 1
+          fi