Lucie / minute1d ago

hell yeah, got displayport alt mode over usb-c working on rk3588 pocket reform with mainboard 2.0!

in the end it was a DP lane polarity issue: USB3 allows lane polarity swap for better PCB routing, but DP doesn't. tricky when you need to reuse the same lanes for both.

Show threadLucie / minute1d ago
but wait... does that mean MNT Pocket Reform can have 3 displays now (1 DP, 1 HDMI, 1 internal)? yes, yes it can!
Show threadIgnas Kiela1d ago
@mntmn no DP MST support?
Show threadLucie / minute1d ago
@ignaloidas no, but i also don't have a display that can do that
Show threadWolf480pl
@mntmn
USB-C hubs with multiple display outputs usually use MST, maybe one of those would be easier to get than an MST-supporting display?
@ignaloidas
Apr 9 at 10:26amWeb
Show threadIgnas Kiela1d ago
@wolf480pl @mntmn yeah, my thoughts on usage are the same

Though it seems like rk3588 can't support MST, while the (lower-end) RK3576 can https://lwn.net/Articles/1031560/
Add support for RK3588 DisplayPort Controller

LWN.net
Show threadLucie / minute1d ago
@ignaloidas @wolf480pl yeah i also remember this as a newer feature. also not sure how useful it would be for 2 lanes
Show threadIgnas Kiela1d ago
@mntmn @wolf480pl how high can they clock? You could drive two 1080p monitors with that if it can go to HBR2
Show threadWolf480pl1d ago

@mntmn
If I'm reading the table here
https://en.wikipedia.org/wiki/DisplayPort#Refresh_frequency_limits_for_common_resolutions
correctly ( it's for 4 lanes so divide fps by 2, then by 60 to see how many monitors fit)

with 2 lanes and HBR3 one should be able to get 2x 1440p60Hz, right?

@ignaloidas

DisplayPort - Wikipedia

Show threadIgnas Kiela1d ago
@wolf480pl @mntmn yeah, and it seems like rk3588 does support HBR3 so it should be able to do it, and that's certainly useful

Also supports DSC if we want to go that route as well