The Kernel command line option kgdbwait makes kgdb wait for a debugger connection during booting of a kernel. You can only use this option you compiled a kgdb I/O driver into the kernel and you specified the I/O driver configuration as a kernel command line option. The kgdbwait parameter should always follow the configuration parameter for the kgdb I/O driver in the kernel command line else the I/O driver will not be configured prior to asking the kernel to use it to wait.

The kernel will stop and wait as early as the I/O driver and architecture allows when you use this option. If you build the kgdb I/O driver as a loadable kernel module kgdbwait will not do anything.