This file is indexed.

/lib/firmware/atusb/ChangeLog is in linux-firmware 1.157.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

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ChangeLog:
	* 0.0  initial release
	* 0.1  addition of ATUSB_TEST
	* 0.2  First public release. Compatible with atusb driver in the
	  upcoming 4.2 kernel

To flash the firmware you need dfu-util on the host:
dfu-util -d 20b7:1540 -D atusb-0.2.dfu

The firmware is flashed into permanent storage and does not need to be provided
after power off. A new firmware version can be flashed the same way.

Firmware source code is GPLv2+ and can be found here:
http://projects.qi-hardware.com/index.php/p/ben-wpan/source/tree/master/atusb/fw