'disco' is no longer supported so let's drop that.
Next please run this command on the affected system so we can find out
more about it:
apport-collect 1873541
** Tags removed: disco
** Package changed: gdm3 (Ubuntu) => mutter (Ubuntu)
** Changed in: mutter (Ubuntu)
Status: New => Incomplete
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https://bugs.launchpad.net/bugs/1873541
Title:
black screen with cursor on dual nouveau + i915
Status in mutter package in Ubuntu:
Incomplete
Bug description:
This bug should be able to be reproduced on any computer with both an
nvidia (stock nouveau) and intel igpu (stock i915), booting to stock
gdm3 (wayland by default). My main example is a MacBookPro6,2 with the
infamous GT 330m on 20.04 with -proposed enabled and booting with the
following grub manipulations to set gmux to the integrated LVDS:
outb 0x710 2 - switch LVDS to intel
outb 0x728 1 - switch internal DDC to intel
outb 0x740 2 - switch displayport out to intel
I am not using outb 0x750 0, so that the 330m remains powered on. It
still works just fine-- the only thing broken is the LVDS connection
to the internal panel. I disable it with video=LVDS-2:d.
--> NOTE: This mod is only for the convenience of not having to deal
with a phantom second screen once booted (both GPU's have the LVDS and
edid of the internal screen hooked up). The computer boots fine and
the bug reproduces exactly the same with or without it.
I tested with all these modifications disabled, and this still
occurred - it's not specific to my configuration. A user booting stock
Ubuntu on this laptop, or as I discovered later, any nouveau + i915
hardware combination will run into this as well.
Anyways, I'm keeping the 330m enabled to use DRI_PRIME to run
applications on the 330m for good reason- it supports OpenGL 3.3 while
HD Graphics (arrandale aka Ironlake) is the only HD Graphics iGPU
stuck on OpenGL 2.1, thus otherwise vastly restricting the modern
graphics workloads of the system.
When explicitly booting with gdm3 WaylandEnable=false (login and
desktop both xorg), everything works as expected - single screen
driven by the i915's KMS, nouveau with DRI_PRIME working, returning
NVA5 stats and functional with OpenGL 3 apps as well.
On GDM3 wayland, however (the default-- which is why I think this bug
is rather important), gdm3 starts to a black screen with cursor. The
login screen and shell still seem to be running-- I can type my
password blindly and press enter and the cursor freezes briefly as it
does during a non-broken login. After a few seconds, I can press the
volume up/down keys and I hear the volume sound. Pressing the app grid
shortcut makes the cursor lag, just as it does when I disable the
nvidia at the pcie link level and rendering works on i915. Backlight
control also works on the login screen and once logged in. It's as if
everything except the actual rendering to the screen is working.
The minute I pass nouveau.modeset=0 in cmdline, or cut the power to
the 330m at the hardware level with outb 0x750, Wayland starts working
again. The issue has something to do with GDM3's handling of a KMS-
enabled nouveau GPU, whether it is headless or not (no difference with
video=LVDS-2:d or not).
To confirm my suspicions that it is not specific to the macbook pro
line, this exact same issue (Xorg works wayland doesn't) also occurred
on a desktop dual-gpu setup, with a GTX 760 (kepler) on nouveau tandem
with a Haswell HD Graphics G3258-- with any combination of displays,
all on the Intel, mixed on nvidia and intel, or all on nvidia, as long
as both cards were present and modesetting, a black screen with cursor
but blindly working gnome followed.
This bug has existed since at least 19.04, if not earlier-- I replaced
the nvidia gpu in that system with a Radeon 7870 when it ran that
release due to this bug, as a matter of fact.
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