Hi Matthias, could you open a ticket at gitlab, providing a dmesg as described at https://gitlab.freedesktop.org/drm/intel/-/wikis/How-to-file-i915-bugs Thanks, Imre On Sun, Feb 20, 2022 at 03:33:56PM +0100, Matthias Walther wrote: > Hm, no ideas on this? > > > Am 28.01.22 um 20:50 schrieb Matthias Walther: > > Hello, > > > > there are a lot of quite similar, low cost USB-C docks with multiple > > display output (usually 2x HDMI + 1x VGA) available on the big online > > platforms such as Amazon, Ebay, and Aliexpress. > > > > Internally the display outputs are connected via DisplayPort. If you > > connect a monitor to one of the ports, it's detected as display port > > connection in xrandr. Always the same dpX in xrandr, independently of > > which physical port in use. This suggests that all physical outputs are > > connected to the same DisplayPort output. > > > > On Microsoft's Windows these docks support multi headed output, like a > > different image on all displays (called expand mode in Windows). However > > the vendor advertises, that on MacOS the adapter can only display the > > same image on all ports of the adapter. This might be a hint, that the > > adapter internally uses DisplayPort's Multi-Stream Transport (MST) > > technology for the second and third display output (2nd HDMI, VGA), as > > Apple does not support MST while Microsoft does. Linux behaves just like > > MacOS here and only mirrors the image. > > > > Linux is supposed to support MST since like around 2014. There are > > parameters to enable it for i915, e. g. i915.enable_dp_mst={1,2}. > > > > However unfortunately those USB-C docks do not support multi-headed > > output on Linux. The second monitor is not detected, there is just a > > mirrored image of the first monitor on monitor two and three. > > > > Does Linux support MST over Thunderbolt 3/4? Is there maybe a hidden > > command that the Windows driver uses to switch MST on in the dock's > > chipset? > > > > Any hints on how to debug this would be highly appreciated! Those > > adapters become more and more popular, they are affordable and it would > > be awesome to make them fully work with Linux. > > > > Best, > > Matthias > > >
