From which register, I can know the camera is online?

There is a state that no camera is existed and only csi clock and data is connected with Xavier.
I try to get the value of VI_CSIMUX_STAT_FRAME_0. I try the command ./reg 0x15c144a4 and ./reg 0x15c054a4, and kernel all crashed. (the reg is get from Accessing registers from Linux).How can I get the value of the reg VI_CSIMUX_STAT_FRAME_0?