>> Hmm. My MST-foo is admittedly weak so I'm not sure. A quick trawl through >> the spec didn't provide any solid explanations either :( However eg. >> "Figure 2-83: Example Multi-function MST Branch-Sink Device Enumeration" >> in the DP 1.4 spec does appear to show kind of virtual DPCD thing behind >> a logical port. But I'm not really sure what than means. > > Good point, I'm gonna dig more into that. It sounds like we should be > able to access that with the relative addressing as defined by the spec > (2.11.5). I'll have to see why that's currently getting nacked though. > It looks like DPCD reads on logical ports work on some devices, and not others... I swapped my MST display out with a different one, and it read just fine. More specifically - in a daisy chain setup with 2 MST displays - with the one that works at the end: # auxrw.py read /dev/drm_dp_aux4_mst\:0-1-8 0x30-0x3f -> ACK # auxrw.py read /dev/drm_dp_aux6_mst\:0-1 0x30-0x3f -> ACK (The GUIDs returned are identical) With the one that doesn't at the end: # auxrw.py read /dev/drm_dp_aux4_mst\:0-1-8 0x30-0x3f -> *NAK* # auxrw.py read /dev/drm_dp_aux6_mst\:0-1 0x30-0x3f -> ACK So it seems there's some device dependent behavior here. I'm not sure if there's a better way of handling this besides exposing all the downstream ports: If it works, great. If not, just don't use it? Leo _______________________________________________ amd-gfx mailing list amd-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/amd-gfx
