I'm playing with a gg11.
The SDK can be downloaded via Simplicity Studio.
udev rules can be found from SEGGER JLink or Simplicity Studio.
Linux binaries can be found from SEGGER's JLink.
$ /usr/bin/JLinkExe
J-Link> connect
Device> EFM32GG11B820F2048
TIF> SWD
Speed> 12000
J-Link> loadbin foobar.bin, 0
Press the physical reset button and marvel.
The following reads printfs and such from VCOM on my linux computer. I haven't tried writing yet.
$cat /dev/ttyACM0
EFM32 Giant Gecko 11 USART4 example
Virtual COM port enabled.