CI: separate image for docker cache (#30413)

just registry cache

selfdrive/test/docker_build.sh

@@ -17,7 +17,15 @@ fi
 
 source $SCRIPT_DIR/docker_common.sh $1 "$TAG_SUFFIX"
 
-DOCKER_BUILDKIT=1 docker buildx build --platform $PLATFORM --load --cache-to type=inline --cache-from type=registry,ref=$REMOTE_TAG -t $REMOTE_TAG -t $LOCAL_TAG -f $OPENPILOT_DIR/$DOCKER_FILE $OPENPILOT_DIR
+if [ -n "$PUSH_IMAGE" ]; then
+  REG_CACHE="--cache-to type=registry,ref=$REMOTE_CACHE_TAG,mode=max"
+fi
+
+DOCKER_BUILDKIT=1 docker buildx build --platform $PLATFORM --load \
+  --cache-from type=registry,ref=$REMOTE_CACHE_TAG \
+  --cache-from type=registry,ref=$REMOTE_TAG \
+  $REG_CACHE \
+  -t $REMOTE_TAG -t $LOCAL_TAG -f $OPENPILOT_DIR/$DOCKER_FILE $OPENPILOT_DIR
 
 if [ -n "$PUSH_IMAGE" ]; then
   docker push $REMOTE_TAG

selfdrive/test/docker_common.sh

@@ -22,3 +22,4 @@ TAG_SUFFIX=$2
 LOCAL_TAG=$DOCKER_IMAGE$TAG_SUFFIX
 REMOTE_TAG=$DOCKER_REGISTRY/$LOCAL_TAG
 REMOTE_SHA_TAG=$DOCKER_REGISTRY/$LOCAL_TAG:$COMMIT_SHA
+REMOTE_CACHE_TAG=$DOCKER_REGISTRY/$LOCAL_TAG:cache