DisplayLink USB 2.0

Why this thread was started (Dec 2020):

Quote
bodhi

DisplayLink USB 2.0 display adapters driver (UDLFB driver) will be removed in future kernel.

https://lists.freedesktop.org/archives/dri-devel/2020-November/289574.html

Not sure when this will be in effect, but it will. UDL DRM driver is the replacement. But I guess a lot of old embedded systems still reply on UDLFB to drive a USB monitor.

Now (Dec 2024), please see this post below about UDL DRM.

-bodhi
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Edited 2 time(s). Last edit at 12/29/2024 01:47PM by bodhi.

thats gonna hurt a few people.....

Gravelrash Wrote:
-------------------------------------------------------
> thats gonna hurt a few people.....

I know! we have a similar situation with the HP T5325 and T5335z. The old Dove FB is no longer usabe in the new kernel (I attempted to bring it back but realized it is not worth it). So DRM or nothing. In a way, it is good for us to figure out how to use it on T5335z because it will be a valuable experience for furture hacks.

For the DisplayLink, people who try to use it in latest kernel will hopefully have a place where they can get helps.

-bodhi
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So, just went through this battle. I can say, the new DRM version of the driver works well, damage is supported, screen corruption seems minimal. Running Firefox remote to my GoFlex via direct tcp X11 (no SSH tunnel) I was able to do full screen video at 1280x720. Now, on the pain side for some reason the DRM driver seems REALLY dumb about picking outputs and screen modes vs the older FB version that would usually pick something at least usable if not a match to the monitor.

Now, theoretically my old SIS2VGA was depreciated with 6.2... it's still in kernel as of 6.12, still just as slow and undocumented but they haven't nuked it yet. (Note, most distros also blacklist it's modules by default.)

Kurlon,

> So, just went through this battle. I can say, the
> new DRM version of the driver works well, damage
> is supported, screen corruption seems minimal.
> Running Firefox remote to my GoFlex via direct tcp
> X11 (no SSH tunnel) I was able to do full screen
> video at 1280x720.

Cool! it would be great if you can post your kernel and xorg config.

I've not done anything for the Dove DRM on HP T5335z. But if I do in the future, nice to have something DRM to cross reference.

-bodhi
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My current setup I don't use an xorg conf, I let it auto-detect and it correctly identifies the card as 'modesetting'.

Once the box is booted, you may need to kick the displaylink device to get it out of 'presetup' mode acting like a mass storage device with an antique Windows installer on it an into video mode. I do this via udev rule:

/etc/udev/rules.d/60-displaylink.rules

ATTR{idVendor}=="17e9", ATTR{bConfigurationValue}=="2", RUN+="/usr/bin/dlconfig %p"

/usr/bin/dlconfig

#! /bin/bash
if [ -e /sys$1/bConfigurationValue ]; then
#    /sbin/modprobe udlfb console=1 fb_defio=1 shadow=0
    echo 1 > /sys$1/bConfigurationValue
fi;

The commented line is for getting the older FB driver up and going with a console, but aren't needed for the DRM driver. You can check if your system sees a display with the following:

root@gfn:~# for p in /sys/class/drm/*/status; do con=${p%/status}; echo -n "${con#*/card?-}: "; cat $p; done
VGA-1: connected

In my case the card is live, VGA output. Both of my docs, an HP and Kensington both only claim to have VGA output, even when using DVI-I only devices connected to them. If you get this far but don't have a working video signal, you can force the video mode by adding a kernel command line to uEnv.txt:

/boot/uEnv.txt

custom_params=video=VGA-1:1280x720@60

https://wiki.archlinux.org/title/Kernel_mode_setting has good docs for this, as this is a fully functioning KMS device now, all the tricks work with it. Kernel config attached, it has both the old and new Displaylink drivers added, along with my SIS2VGA.

Because the video device isn't active until later in boot, once udev is live and processing, the normal start routine for say lightdm fires off way too soon to see video, so at the moment I'm logging in via console and just kicking off startx manually. I'll have to chase this a bit later, though really with only 128MB RAM this box is at it's limits trying to be a proper workstation. Also, if you're going to forward X to this machine from remote without an SSH tunnel, you'll need to edit /etc/X11/xinit/xserverrc to change nolisten to listen, and be aware of the giant security hole doing so creates.

Kurlon,

Very nice!

There are countless numbers of USB DisplayLink users out there who will benefit from this.

I'll change the thread subject and make this a sticky thread.

-bodhi
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