We should enhance docs here: https://docs.openshift.com/serverless/1.29/knative-serving/config-applications/pvcs-for-serving.html with the type of volumes that are supported.

• secret
• configmap
• projected (downwardAPI, ServiceAccountToken etc)
• emptydir
• pvc

We dont support directly volume sources like: hostpath, generic ephemeral, 

AWSElasticBlockStore, GCEPersistentDisk etc. Ceph support level should be also described.