CI: kernel: build only changed targets

Detect changes in commit and build only changed targets.
If a change is related to the generic target, build test each target.

The matrix json is split. For target check patch only the first
subtarget is selected, for build test each target subtarget is built.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

.github/workflows/kernel.yml

@@ -16,7 +16,7 @@ on:
       - '.github/workflows/kernel.yml'
       - 'include/kernel*'
       - 'package/kernel/**'
-      - 'target/linux/generic/**'
+      - 'target/linux/**'
 
 permissions:
   contents: read
@@ -26,33 +26,66 @@ jobs:
     name: Set targets
     runs-on: ubuntu-latest
     outputs:
-      target: ${{ steps.find_targets.outputs.target }}
+      targets_subtargets: ${{ steps.find_targets.outputs.targets_subtargets }}
+      targets: ${{ steps.find_targets.outputs.targets }}
 
     steps:
       - name: Checkout
         uses: actions/checkout@v3
+        with:
+          fetch-depth: 2
+
+      - name: Get changed files
+        id: changed-files
+        uses: tj-actions/changed-files@v35
+        with:
+          since_last_remote_commit: true
 
       - name: Set targets
         id: find_targets
         run: |
+          export TARGETS_SUBTARGETS="$(perl ./scripts/dump-target-info.pl targets 2>/dev/null \
+            | sort -u -t '/' -k1 \
+            | awk '{ print $1 }')"
+
           export TARGETS="$(perl ./scripts/dump-target-info.pl targets 2>/dev/null \
             | sort -u -t '/' -k1,1 \
             | awk '{ print $1 }')"
 
-          JSON='['
+          JSON_TARGETS_SUBTARGETS='['
+          FIRST=1
+          for TARGET in $TARGETS_SUBTARGETS; do
+            if echo ${{ steps.changed-files.outputs.all_changed_files }} | grep -q target/linux/generic ||
+              echo ${{ steps.changed-files.outputs.all_changed_files }} | grep -q $(echo $TARGET | cut -d "/" -f 1); then
+              [[ $FIRST -ne 1 ]] && JSON_TARGETS_SUBTARGETS="$JSON_TARGETS_SUBTARGETS"','
+              JSON_TARGETS_SUBTARGETS="$JSON_TARGETS_SUBTARGETS"'"'"${TARGET}"'"'
+              FIRST=0
+            fi
+          done
+          JSON_TARGETS_SUBTARGETS="$JSON_TARGETS_SUBTARGETS"']'
+
+          JSON_TARGETS='['
           FIRST=1
           for TARGET in $TARGETS; do
-            [[ $FIRST -ne 1 ]] && JSON="$JSON"','
-            JSON="$JSON"'"'"${TARGET}"'"'
-            FIRST=0
+            if echo ${{ steps.changed-files.outputs.all_changed_files }} | grep -q target/linux/generic ||
+              echo ${{ steps.changed-files.outputs.all_changed_files }} | grep -q $(echo $TARGET | cut -d "/" -f 1); then
+              [[ $FIRST -ne 1 ]] && JSON_TARGETS="$JSON_TARGETS"','
+              JSON_TARGETS="$JSON_TARGETS"'"'"${TARGET}"'"'
+              FIRST=0
+            fi
           done
-          JSON="$JSON"']'
+          JSON_TARGETS="$JSON_TARGETS"']'
 
-           echo -e "\n---- targets ----\n"
-           echo "$JSON"
-           echo -e "\n---- targets ----\n"
+          echo -e "\n---- targets to build ----\n"
+          echo "$JSON_TARGETS_SUBTARGETS"
+          echo -e "\n---- targets to build ----\n"
 
-           echo "target=$JSON" >> $GITHUB_OUTPUT
+          echo -e "\n---- targets to check patch ----\n"
+          echo "$JSON_TARGETS"
+          echo -e "\n---- targets to check patch ----\n"
+
+          echo "targets_subtargets=$JSON_TARGETS_SUBTARGETS" >> $GITHUB_OUTPUT
+          echo "targets=$JSON_TARGETS" >> $GITHUB_OUTPUT
 
   build:
     name: Build Kernel with external toolchain
@@ -63,7 +96,7 @@ jobs:
     strategy:
        fail-fast: False
        matrix:
-         target: ${{fromJson(needs.determine_targets.outputs.target)}}
+         target: ${{fromJson(needs.determine_targets.outputs.targets_subtargets)}}
     uses: ./.github/workflows/build.yml
     with:
       target: ${{ matrix.target }}
@@ -79,7 +112,7 @@ jobs:
     strategy:
        fail-fast: False
        matrix:
-         target: ${{fromJson(needs.determine_targets.outputs.target)}}
+         target: ${{fromJson(needs.determine_targets.outputs.targets)}}
     uses: ./.github/workflows/check-kernel-patches.yml
     with:
       target: ${{ matrix.target }}