diff --git a/consensus/clique/clique.go b/consensus/clique/clique.go
index 4db2a27bcb..1b693f75b3 100644
--- a/consensus/clique/clique.go
+++ b/consensus/clique/clique.go
@@ -661,6 +661,7 @@ func (c *Clique) CalcDifficulty(chain consensus.ChainReader, time uint64, parent
 	return CalcDifficulty(snap, c.signer)
 }
 
+// CalcDifficulty returns block difficulty according to local signer is the inturn signer or not.
 func CalcDifficulty(snap *Snapshot, signer common.Address) *big.Int {
 	if snap.inturn(snap.Number+1, signer) {
 		return new(big.Int).Set(diffInTurn)
diff --git a/consensus/ethash/consensus.go b/consensus/ethash/consensus.go
index eef6fb0df2..34f73d1f42 100644
--- a/consensus/ethash/consensus.go
+++ b/consensus/ethash/consensus.go
@@ -291,6 +291,7 @@ func (ethash *Ethash) CalcDifficulty(chain consensus.ChainReader, time uint64, p
 	return CalcDifficulty(chain.Config(), time, parent)
 }
 
+// CalcDifficulty returns block difficulty according to the parent block's time and difficulty.
 func CalcDifficulty(config *params.ChainConfig, time uint64, parent *types.Header) *big.Int {
 	next := new(big.Int).Add(parent.Number, big1)
 	switch {