Hi Dave,
Thanks for your advice.
I tried to set 0x95[0~7] = 0xff, and found out the bit [6~7] works.
* BIT 7; DDC Controller Error Interrupt
* BIT 6; BKSV Flag Interrupt
HPD is high when setting the 0x95.
It looks like among all the bits of 0x95, only the ones related to CEC don't work. So I guess there might be certain setting not mentioned in datasheet, when enabling the CEC interrupt.
Phil