Firmware blobs root directory

configname: CONFIG_EXTRA_FIRMWARE_DIR

Linux Kernel Configuration
└─>Device Drivers
└─>Generic Driver Options
└─>Firmware loader
└─>Firmware blobs root directory
In linux kernel since version 2.6.27 (release Date: 2008-10-09)  
This option controls the directory in which the kernel build system
looks for the firmware files listed in the EXTRA_FIRMWARE option.