The TP-Link TD-W8980 is an ADSL Annex A and VDSL router. Beside the wifi hardware, the router is very similar to the TD-W8970. The OEM source code is available at: GPL_TD-W8980.tar.gz.
The 5GHz WAVE300 chipset is not yet supported by OpenWrt. Everything else should work.
Do not upgrade to the 12.10.2013 (or newer) TP-Link firmware if you intend to switch to OpenWrt via the TP-Link webinterface. Starting with 12.10.2013 the TP-Link webinterface accepts only RSA signed firmware images with the v3 header.
The RSA Signature is not enforced/validated by u-boot. Therefore, flashing over serial & bootloader still works.
If the device is running firmware version lower than 12.10.2013, OpenWrt can just be installed via the firmware update mechanism in the web interface. Otherwise, you can explore web interface shell injection, as mentioned in TP-Link TD-W9980.
As mentioned there, you need to split image sysupgrade into two, flashing the first part into mtdblock1 and the other one into mtdblock2.
Temporarily connect the left side of R225 to GND (confirmed working; the image above has the wrong pad circled – use the pad immediately to the left of the circle in the image), to get into UART mode. You should see a message similar to this: