What do you mean by PDSCH layers?
Data layers that are sent to UE.
2 PDSCH layers is one beam.
2 PDSCH Layer per beam for 2x2 MIMO.
For 4x4 MIMO it will be 4 PDSCH layers per beam.
Correct?
No, one beam can handle max 2 data layers +45 and -45 degrees polarization.
Do you mean for MU MIMO?
I will have to check. Pretty sure 4x4 Mimo per beam is possible. But you could be right.
For both MU-MIMO and SU-MIMO: one beam means maximum 2 data layers.
Yes always 2 only for SSB beams.
But 1 SSB beams = 4 csi-rs beams which again 8 layers with 1 SSB beam.
Yes, true, for 4 csi-rs beams can be 8 layers.
This is what I also said: each beam has maximum 2 layers of data.
In my opinion no network using csi-rs beams as of now.
Anyone seen such network? Please share experience.
You can read this article.
It will help you understand type of beams:
Nice one! 
What you need to understand that it is important the CSI-RS ports.
For example if we have 8 csi-rs ports than signal, same signal, will be transmitted from each of the csi-rs ports with phase shift so it will sum up at one rx antenna and it will not sum-up at the rest of all rx antenna.
But now there are vendors that have even 32 csi-rs ports in 5G which is huge that creates very sharp beams with very high SINR.
Excellent article.
Csi-rs beams and port not to mix as UE used port as per no of csi-rs RE to be used for CSI calculation.
So have one question like as you mentioned ‘in good RF conditions SRS based weights are used and in weak RF conditions PMI based weights are used’. Then on good RF condition which is desirable 2nd beam based ssb/csi-rs or 1st beam based on SRS weighs?
SRS based as of now not used in NR for assigning weight to Antenna elements.
As of now fixed weight used as per CSI reported using GoB concept.
SRS based seen with LTE for massive MIMO.
For NR SRS based under development or trial.
By weight it mean long term and short term weights.
Ok got you, thanks.
So we have only 2nd option now beam based on ssb/csi-rs.
Yes, exactly.
SRS based weights can be used and switched with PMI depending on the radio conditions as you mentioned, but this applies for PDSCH beams where dynamic weight is used, while broadcast and common control channels are using predefined static weight and this is the implementation of Huawei as far as I know.
Yes usually SRS based is in good RF while PMI based is in bad RF.
This is decided based on UL SINR.
You can see a plot here:
Live Draw - online drawing board - Draw, Share, Collaborate! how beamforming is made .
But it is better explained on Sharetechnote here:
The picture above is most important to understand beamforming precoding and everything!
Also one need to understand that it all depends on multipaths and air interface matrix.
Otherwise there would be MIMO 4x4 everywhere.
But it is the air interface matrix that limits the rank.