Which external GPS logger for a Panasonic Lumix G9?

Which external GPS logger can I connect to the Panasonic Lumix G9 for real time geotagging without a smartphone?

With external GPS logger, I mean devices like

• Qstarz GPS BT-Q1000XT
• TSI GL-770
• …

Currently I use a Garmin GPSMap to track the position and tag the photos offline while post processing the exif tags with Digikam and similar tools on Linux.

Is there a specific protocol which the GPS logger needs to support?