PTP Hardware Clock (PHC)

configname: CONFIG_IGB_PTP

Linux Kernel Configuration
└─>Device Drivers
└─>Network device support
└─>Ethernet driver support
└─>PTP Hardware Clock (PHC)
In linux kernel since version 3.5 (release Date: 2012-07-21)  
Say Y here if you want to use PTP Hardware Clock (PHC) in the
driver. Only the basic clock operations have been implemented.

Every timestamp and clock read operations must consult the
overflow counter to form a correct time value.