Channel correlation calculation based on CSI (PMI) or to SRS Uplink?

Hello All.

I am reading 5G Huawei documentation and I am getting confused by this phrase:

“Channel correlation is calculated based on uplink feedback and can be considered as channel similarity”.

Does it refers to CSI (PMI) or to SRS uplink? Anyone having a clue?

It should be SRS as it talks about calculation.