1. For the 18 HPD_IRQ on the HPD signal and only 17 IRQ report on CC package. Could you please send the completely CC log of the negotiation (Power negotiation, Enter Alt Mode, DP config, DP status, Attention.) and then, we can working together to see whether the HPD information was reported or not.
2. For the DisplayPort Alt Mode over Type-C SPEC, there are two DisplayPort Status flags are defined to communicate HPD state:
HPD_State – Indicates whether HPD’s logical state is high or low (denoted as HPD_High or HPD_Low, respectively).
IRQ_HPD – Indicates an IRQ_HPD.
It is follow DisplayPort Alternative mode over Type-C SPEC.
3. The IRQ define on DisplayPort SPEC,
A Sink device, when issuing an IRQ (Interrupt ReQuest) to the Source device, must generate a low-going HPD pulse of 0.5ms through 1ms in duration. Upon detecting this “IRQ_HPD pulse”, the Source device must read the DPCD Link/Sink Device Status registers and take corrective action.