fallback to SW cursor on GPU hotplug

[Aleksander Miera]

I guess the title is pretty much self-explanatory.
The issue has been discovered while connecting EVDI-backed device (https://github.com/DisplayLink/evdi) with a running Xorg session and led to filing of https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/1870512
However, fixing the issue with SW cursor is only a partial solution in that case, as sticking to SW cursor can potentially hinder performance.

I am aware of this (dix/dispatch.c):
    update_desktop_dimensions();

    /*
     * We cannot register the Screen PRIVATE_CURSOR key if cursors are already
     * created, because dix/privates.c does not have relocation code for
     * PRIVATE_CURSOR. Once this is fixed the if() can be removed and we can
     * register the Screen PRIVATE_CURSOR key unconditionally.
     */
    if (!dixPrivatesCreated(PRIVATE_CURSOR))
        dixRegisterScreenPrivateKey(&cursorScreenDevPriv, pScreen,
                                    PRIVATE_CURSOR, 0);

    return i;
}

as well as several other similar places in Xorg's code. Question is: how big effort would it be to actually fix this?
Should this be reported/consulted with the upstream directly maybe?

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: xserver-xorg-core 2:1.20.7-2ubuntu2
ProcVersionSignature: Ubuntu 5.4.0-21.25-generic 5.4.27
Uname: Linux 5.4.0-21-generic x86_64
ApportVersion: 2.20.11-0ubuntu21
Architecture: amd64
BootLog: Error: [Errno 13] Permission denied: '/var/log/boot.log'
CompositorRunning: None
CurrentDesktop: ubuntu:GNOME
Date: Fri Apr 3 12:45:07 2020
DistUpgraded: Fresh install
DistroCodename: focal
DistroVariant: ubuntu
ExtraDebuggingInterest: Yes, including running git bisection searches
GraphicsCard:
 Intel Corporation 4th Gen Core Processor Integrated Graphics Controller [8086:0416] (rev 06) (prog-if 00 [VGA controller])
   Subsystem: Dell 4th Gen Core Processor Integrated Graphics Controller [1028:060d]
   Subsystem: Dell GK107GLM [Quadro K1100M] [1028:060d]
InstallationDate: Installed on 2020-03-30 (4 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Alpha amd64 (20200329)
MachineType: Dell Inc. Dell Precision M3800
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.4.0-21-generic root=UUID=1b7a03b4-95ff-4d1b-9897-848a0dc6f8b9 ro quiet splash vt.handoff=7
SourcePackage: xorg-server
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 05/25/2018
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A12
dmi.board.name: Dell Precision M3800
dmi.board.vendor: Dell Inc.
dmi.board.version: A12
dmi.chassis.type: 8
dmi.chassis.vendor: Dell Inc.
dmi.chassis.version: Not Specified
dmi.modalias: dmi:bvnDellInc.:bvrA12:bd05/25/2018:svnDellInc.:pnDellPrecisionM3800:pvrA12:rvnDellInc.:rnDellPrecisionM3800:rvrA12:cvnDellInc.:ct8:cvrNotSpecified:
dmi.product.name: Dell Precision M3800
dmi.product.sku: Dell Precision M3800
dmi.product.version: A12
dmi.sys.vendor: Dell Inc.
version.compiz: compiz N/A
version.libdrm2: libdrm2 2.4.100-4
version.libgl1-mesa-dri: libgl1-mesa-dri 20.0.2-1ubuntu1
version.libgl1-mesa-glx: libgl1-mesa-glx N/A
version.xserver-xorg-core: xserver-xorg-core 2:1.20.7-2ubuntu2
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:19.1.0-1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20190815-1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.16-1

[Daniel van Vugt (vanvugt)]

Please report it upstream:

  https://gitlab.freedesktop.org/groups/xorg/-/issues

and then tell us the new bug ID.

[Aleksander Miera (amiera)]

Reported, issue ID 1008: https://gitlab.freedesktop.org/xorg/xserver/-/issues/1008