USB GPU bugs

Pekka Paalanen ppaalanen at
Fri Oct 11 10:13:42 UTC 2019

On Thu, 10 Oct 2019 09:40:30 +0200
Hans de Goede <hdegoede at> wrote:

> Hi,
> On 09-10-2019 12:23, Pekka Paalanen wrote:
> > On Wed, 9 Oct 2019 09:59:29 +0200
> > Hans de Goede <hdegoede at> wrote:  
> <snip>
> >> 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.  
> > 
> > In my case, I see an "add" and three HOTPLUG events via udev when I
> > hotplug the DisplayLink dock and it creates the DRM device node on the
> > spot. Mutter receives just one RandR event though, which it deems is
> > not a hotplug, and looking at the config timestamps I think the event
> > indeed is reflecting too old state. 'xrandr' will show everything about
> > the new connector just fine though, IIRC.  
> I just realized I should probably respond to this bit. You see that
> after "xrandr" everything looks ok, but the "xrandr" command causes
> a round trip to the kernel and even causes the kernel to re-poll all
> connectors. Have you tried "xrandr --current" ? That will return the
> current state stored inside the xserver without re-querying the kernel.
> Not sure of this helps, but I thought I should mention it.

Hi Hans,

that's a good hint. 'xrandr --current' reports the connector as
connected and with a good looking mode list, when Mutter does not
autoenable it.

Does 'xrandr' call into the kernel with drmModeGetConnectorCurrent(),
or does it really return only what Xorg had internally cached? If it
calls into kernel, then I'm not surprised it returns the good info,
since I believe that Xorg is somehow ignoring a udev hotplug event, or
not realizing that something did still change since the last time it
sent out RandR events.

I finally created an upstream issue for this one:

I'll continue staring at it next week.

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