I know it's supported. 
Moreover I was trying to enable the internal GMAC to the Broadcom CPU (probably the only consumer device to have 3 gmac) to get VDSL working (https://forum.openwrt.org/t/ipq806x-lede-support-for-tp-link-archer-vr2600v/326/25).
I tried to change some code accordingly to the TP-Link sources, but didn't work. I hope that switching to this gmac implementation can solve the problem. 