Arch Linux

abc12345

Member

Registered: 2022-03-30

Posts: 57

Add USB VGA display after driver compiled

Hi. What must be done to attach a USB VGA monitor to the OS after the kernel driver is compiled? I compiled a FL2000 USB VGA dongle driver and my dmesg indicates the driver is loaded and is detecting when I plug in the monitor, but the monitor plugin event is ignored. So there's nothing in OS to work with an external USB VGA monitor. xrandr only shows the internal monitor. What am I missing? Thanks.
PS. I saw DisplayLink seems related but does it have to be a specific brand of a USB VGA dongle for that?

Last edited by abc12345 (2022-04-12 10:29:41)

Lone_Wolf

Administrator

From: Netherlands, Europe

Registered: 2005-10-04

Posts: 14,898

Re: Add USB VGA display after driver compiled

I compiled a FL2000 USB VGA dongle driver and my dmesg indicates the driver is loaded and is detecting when I plug in the monitor,

Which package did you use to build the driver ?

Show us the dmesg and the output of lsusb --tree --verbose with the monitor plugged in.

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abc12345

Member

Registered: 2022-03-30

Posts: 57

Re: Add USB VGA display after driver compiled

I returned the dongle. But for the sake of discussion, what would be the next steps anyway?
This is what I compiled: https://aur.archlinux.org/packages/fl2000-dkms
lsusb would show the adapter, dmesg would show monitor plugin event.

Lone_Wolf

Administrator

From: Netherlands, Europe

Registered: 2005-10-04

Posts: 14,898

Re: Add USB VGA display after driver compiled

Converters like these require several things to work :
A a protocol to allow dispay signals to be transported over an usb connection
B convert the signal from usb to a display standard usable by monitors.
C a videocard to generate the display signal

B can be done in the monitor, but is more often done by the converter

The fl2000 linux driver does A + B , but lacks C .

converters that do work under linux include a drm driver that acts as an extra videocard.
xrandr --listproviders should show the new videocard (no idea about wayland) .

DisplayLink over USB2 used an in-kernel driver, but their USB 3 driver is proprietary out-of-tree .
Both are opensource.
Not sure which dongles use DisplayLink tech, but if they do the dongle documentation should mention DisplayLink.

Fortunately things are improving.
There is an open standard that allows DisplayPort signals to be transferred over usb-c cables with 2 HW implementations which have opensource kernel drivers.

USB 3 :   Thunderbolt 3 & USB alt mode
Both are optional, thunderbolt tends to be present mostly on high end HW, while USB alt mode is more common

USB4 ports must support both Thunderbolt4 and USB alt mode.

Assuming your system has an USB-C port with DP support, you can connect any monitor with a DisplayPort connector.
DP to VGA/HDMI/DVI converters shouild also work with such ports.

For systems with thunderbolt 3 ports, thunderbolt docks are a good option.

Edit :
corrected displaylink part.
Thank you for clarifying, progandy.

Last edited by Lone_Wolf (2022-04-13 14:36:50)

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Disliking systemd intensely, but not satisfied with alternatives so focusing on taming systemd.

clean chroot building not flexible enough ?
Try clean chroot manager by graysky

progandy

Member

Registered: 2012-05-17

Posts: 5,307

Re: Add USB VGA display after driver compiled

DisplayLink over USB2 used an in-kernel opensource driver, but their USB 3 driver is proprietary.
I am not sure if DisplayLink shares their tech with other manufacturers, but the dongle documentation should make that clear.

The part that simulates a graphics output is open source (called evdi). It might be possible to write some glue code to send the data to the fl2000 driver, but that might not be trivial.
Some more discussion here  https://github.com/FrescoLogic/FL2000/issues/12

@abc12345: Do not expect amazing results with such devices. uncompressed 1920x1080@60Hz video is the maximum that can be done with pure USB3 without alt-mode. (If the dongle supports some sort of compression a bit more might be possible)

Thunderbolt / the USB alt-mode is much better, since it is a "real" display port directly connected to the graphics card without forcing the data through ram and cpu bottlenecks.

Last edited by progandy (2022-04-13 13:42:36)

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abc12345

Member

Registered: 2022-03-30

Posts: 57

Re: Add USB VGA display after driver compiled

Thank you all.
@progandy The whole idea was to use a monitor without using a graphics card. So there's definitely growth in this USB VGA direction, not necessarily to the liking of some.