How will "USB 3.1 TYPE-C TO VGA ADAPTER" device be recognized by the linux pc?


#1

Hello, my question is that
will your “USB 3.1 TYPE-C TO VGA ADAPTER” add new port to my existing video device:

├─/sys/devices/pci0000:00/0000:00:02.0/drm/card0
│ [MASTER] drm:card0
│ ├─/sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-DP-1
│ │ [MASTER] drm:card0-DP-1
│ ├─/sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-HDMI-A-1
│ │ [MASTER] drm:card0-HDMI-A-1
│ ├─/sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-HDMI-A-2
│ │ [MASTER] drm:card0-HDMI-A-2
│ ├─/sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-HDMI-A-3
│ │ [MASTER] drm:card0-HDMI-A-3
│ └─/sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-VGA-1
│ [MASTER] drm:card0-VGA-1

or it’ll be presented as additional video device, like your UD-160-A docking station does:

├─/sys/devices/pci0000:00/0000:00:1c.4/0000:03:00.0/usb3/3-2/3-2.1/3-2.1:1.0/drm/card1
│ [MASTER] drm:card1
│ └─/sys/devices/pci00…000:00:1c.4/0000:03:00.0/usb3/3-2/3-2.1/3-2.1:1.0/drm/card1/card1-DVI-I-1
│ [MASTER] drm:card1-DVI-I-1
├─/sys/devices/pci0000:00/0000:00:1c.4/0000:03:00.0/usb3/3-2/3-2.1/3-2.1:1.0/graphics/fb1
│ [MASTER] graphics:fb1 “udldrmfb”

??

It isn’t clear how “DisplayPort Alternate Mode” will work, maybe it’s time to buy one of the compatible motherboards, few USBC-VGA adapters and usb type-c hubs and make new much faster multi-seat configuration capable of using gpu acceleration?

I’m steel using UD-160-A.
Not so long ago it started to work slightly better in terms of displaying 1920x1080 video - many thanks to whoever responsible for this.

I’m looking forward to your products, they are much more fun to play with than all that over-expensive gadgets from modern day IT corporation.


#2

Hi Sergey,

Thank you for asking! USB-C Alternate Mode graphics adapters will look like an additional output on your main GPU. So more like your first tree of devices, not the second.

This is because at a physical level, DisplayPort lanes of the GPU must be physically routed out over your motherboard PCB to the USB-C port to support Alternate Mode – and then the USB-C cable carries that DisplayPort signal out of the wire on dedicated lines (as part of Alternate Mode negotiation, 1-4 of the superspeed data pairs in the USB-C cable are dedicated for use by the Alternate Mode).

That means Alternate Mode adapters can achieve better performance (performance should be equal to the GPU-attached screens), *however* only one or perhaps two USB-C alternate mode displays can be attached to a system, up to the maximum number of displays supported by that GPU chip.

Whereas, with virtual USB devices like those based on DisplayLink chips, additional outputs are added at the *software* level and routed over USB bulk packets over the common USB data lines, allowing many additional displays to be added.

So DisplayLink-based docks and graphics adapters will continue to be the only way to get to 4+ displays (without MST) or a multi-seat configuration on Linux.

Hope that background helps, thanks for asking!
Bernie Thompson
Founder, Plugable Technologies


#3