USB GPU bugs

Hans de Goede hdegoede at
Wed Oct 9 07:59:29 UTC 2019

Hi Pekka,

On 09-10-2019 09:47, Pekka Paalanen wrote:
> On Tue, 8 Oct 2019 22:19:45 +0200
> Hans de Goede <hdegoede at> wrote:
>> My main reason for suggesting either one is that I personally am aware
>> of at least 2 issues (both related to secondary USB GPUs handling) which
>> are only present in master and not in the 1.20 branch and which I really
>> would like to see fixed before a new release. I have taking a look at
>> these on my to do list, but not at the top of it (yet).
> Hi Hans,
> it so happens that I am, too, looking at some secondary DRM device
> hotplug issues. I think I've seen three different things: not enough
> RandR events to make Mutter take a hotplugged device & output into use,
> Xorg crash on DRM device hotplug, and failure to start with Xorg USB
> DRM device plugged in.
> Do you have any public records of the issues you have on your plate?

No I've not filed issues yet, since I was planning on debugging them
myself, but if are both seeing these issues then having gitlab
issues to track them might be a good idea.

I am using a gm12u320 based mini projector (Acer C120) for most of
my tests, but I believe that this will reproduce with an udl (USB 2 version)
device too. If necessary I can try to reproduce with an udl device too.

Thinking more about it I'm seeing 3 things:

1. USB GPU is not seen (not shown in xrandr --list-providers, not usable)
    when present before Xorg is started.

2. Hot plugging the USB GPU sometimes causes things to crash shortly

3. Hot unplugging the USB GPU always causes a crash shortly

My test environment is xserver master + mutter/gnome-shell 3.34 on
top of Xorg. Last time I tried downgrading the xserver to 1.20 made all
3 issues go away (*)

I think I might also be seeing some variant of your "not enough hotplug
events" bug. With the gm12u320 projector when hotplugged it is listed
as "unknown" in gnome's display-settings until I change the settings
once and then it becomes "Acer" as it should be. I believe that this
issue is actually also present in the 1.20 branch.



*) Which is why I've not given these bugs a high priority so far

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