[openwrt/openwrt] CI: kernel: use ccache to speedup workflow

[LEDE Commits]

ansuel pushed a commit to openwrt/openwrt.git, branch openwrt-21.02:
https://git.openwrt.org/9718dffd27ea9c15d30958eafef593aab929b7e8

commit 9718dffd27ea9c15d30958eafef593aab929b7e8
Author: Christian Marangi <ansuelsmth at gmail.com>
AuthorDate: Tue Oct 4 18:43:38 2022 +0200

    CI: kernel: use ccache to speedup workflow
    
    Use ccache to speedup kernel compilation.
    Ccache dir is cached across each build test. To refresh ccache directory
    we generate an hash of the kernel include files, that includes the
    kernel versions of every kernel supported and the kernel compile
    includes.
    
    Signed-off-by: Christian Marangi <ansuelsmth at gmail.com>
    (cherry picked from commit 137ba15e6ef31534a2002a02e69b774232f0b040)
---
 .github/workflows/kernel.yml | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/.github/workflows/kernel.yml b/.github/workflows/kernel.yml
index 6c8ad68438..0ba8c27e2e 100644
--- a/.github/workflows/kernel.yml
+++ b/.github/workflows/kernel.yml
@@ -18,6 +18,7 @@ jobs:
     outputs:
       target: ${{ steps.find_targets.outputs.target }}
       owner_lc: ${{ steps.lower_owner.outputs.owner_lc }}
+      ccache_hash: ${{ steps.ccache_hash.outputs.ccache_hash }}
 
     steps:
       - name: Checkout
@@ -30,6 +31,13 @@ jobs:
             | tr '[:upper:]' '[:lower:]')
           echo "::set-output name=owner_lc::$OWNER_LC"
 
+      - name: Generate ccache hash
+        id: ccache_hash
+        run: |
+          CCACHE_HASH=$(md5sum include/kernel-* | awk '{ print $1 }' \
+           | md5sum | awk '{ print $1 }')
+          echo "::set-output name=ccache_hash::$CCACHE_HASH"
+
       - name: Set targets
         id: find_targets
         run: |
@@ -133,6 +141,14 @@ jobs:
           path: openwrt/${{ env.TOOLCHAIN_FILE }}
           key: ${{ env.TOOLCHAIN_FILE }}-${{ env.TOOLCHAIN_SHA256 }}
 
+      - name: Cache ccache
+        uses: actions/cache at v3
+        with:
+          path: openwrt/.ccache
+          key: ccache-kernel-${{ env.TARGET }}/${{ env.SUBTARGET }}-${{ needs.determine_targets.outputs.ccache_hash }}
+          restore-keys: |
+            ccache-kernel-${{ env.TARGET }}/${{ env.SUBTARGET }}-
+
       - name: Download external toolchain
         if: ${{ steps.cache-external-toolchain.outputs.cache-hit != 'true' }}
         shell: su buildbot -c "sh -e {0}"
@@ -153,6 +169,7 @@ jobs:
           echo CONFIG_ALL_KMODS=y >> .config
           echo CONFIG_DEVEL=y >> .config
           echo CONFIG_AUTOREMOVE=y >> .config
+          echo CONFIG_CCACHE=y >> .config
 
           ./scripts/ext-toolchain.sh \
             --toolchain ${{ env.TOOLCHAIN_FILE }}/toolchain-* \