Some H6 board using RGB port to connect display. from one board I have ,it using RGB port (PD0-PD21) connect Ti DLP3435 , so to support that board ,it need mainline support RGB Display output , then use i2c send some command to dlp3435.(Vendor kernel using opt3435 driver to do that but I can't find source code, only firmware provided)
But now mainline currectly not support RGB output . although it support ,it will also encounter a conflict problem. rgmii phy(RTL8211) share the same pins with RGB port (PD0-PD21).
Anyway , I guess support this type board Display need a long way to go .