Kyösti Mälkki has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/31450 )
Change subject: lenovo/g505s: Add the discrete VGA support for AMD Lenovo G505S laptop ......................................................................
Patch Set 4:
Patch Set 3:
Patch Set 3:
GPIO59 can be used to detect presence of DGPU.
Sorry but G505 and G505S are different laptops, here is a correct datasheet for G505S - LA-A091P motherboard - http://www.s-manuals.com/pdf/motherboard/compal/compal_la-a091p_r1.0_schemat... . I don't know how to find a correct GPIO there... but it is not necessary anymore: see comment above, it turned out we could set BottomIO to 0xD0 for all G505S
Page 36 middle-right BRDID and it's 4-state analog input Vab on KB9012 embedded controller. Maybe something you can find from ACPI / EC commands.
OT: Have you poked on EC_TX and EC_RX signals? I *think* you would need some 10k or so pull-up, see comment on page 30.