Over the years, none of the Replicant contributors have been able to find the time to add support for this chip,and at the time of writing this chip is still not supported by Replicant despite being relatively easy to add support for it compared with the Broadcom GPS chips that are present in the other supported devices.
Over time, contributions from other people and projects made it easier to add support for the GSD4t chip.
There is now some documentation of that protocol in the form of some Perl source that can probably decode the protocol, and there has also been some people doing research on it.
In addition it's also easier to do some tests on GNU/Linux: there is now some support in upstream Linux for the Galaxy SII (GT-I9100) thanks to the postmarketOS contributor(s) who worked on that. The nonfree bootloader of the Galaxy SII (GT-I9100) might requires some patches on top of that, but we also maintain patches for the Galaxy SIII (GT-I9300 and GT-I9305) bootloaders in our kernel_replicant_linux repository that might also work on the Galaxy SII (GT-I9100).
The Replicant developers are mostly available on the Replicant mailing and on IRC (#replicant on the hackint, libera.chat and OFTC networks). See the CommunityAndContacts wiki page for more details.
As for how to integrate the work, we already have an example of GPS library that was used in Replicant 4.2 for the GTA04.
As postmarketOS is also interested in making this chip work with free software, it might be a good strategy to also consult them to see how that work could also benefit GNU/Linux distributions.
edit1: removed duplicated title.
License: CC-BY-SA 3.0 Unported