[Nouveau] Cannot start a secondary Xserver with resolution 6480x3840

[Janek Kozicki]

Hi,

In my workflow I am using several separate xservers. One for work,
another for research and so on. Each of them has a separate user
account, and they all belong to the same (main) group called janek.

I've been using nvidia for years, but about 2 years ago some super
annoying bug appeared in nvidia, namely that switching between
virtual terminals sporadically causes nvidia_modeset to freeze all
virtual terminals. Then I can only ssh remotely to investigate the
problem. And rmmod nvidia would not work, or anything else
whatsovever. The only way to unlock virtual terminals is a reboot,
which I hate, because I often have calculations running for months.

So I am hoping that noveau will work now! Alas it is not. When I
configure xrandr to use all my LCD screens in  ~/.xsession using this
command line:

xrandr --output HDMI-1 --off --output DP-1 --mode 3840x2160 --pos 2160x0 --rotate left --output DVI-D-1 --off --output DP-2 --mode 3840x2160 --pos 0x0 --rotate left --output DP-3 --mode 3840x2160 --pos 4320x0 --rotate left

then only single Xserver can start up. Other Xservers have a segfault
upon startup. If I use only one LCD screen then I can start multiple
Xservers, but that is obvioulsy a waste of two screens! :)

The crash log is following:

[   963.513] (EE) 
[   963.513] (EE) Backtrace:
[   963.513] (EE) 0: /usr/lib/xorg/Xorg (xorg_backtrace+0x4a) [0x5566a8b8466a]
[   963.513] (EE) 1: /usr/lib/xorg/Xorg (0x5566a89cb000+0x1bd3f9) [0x5566a8b883f9]
[   963.513] (EE) 2: /lib/x86_64-linux-gnu/libpthread.so.0 (0x7fc673b06000+0x110c0) [0x7fc673b170c0]
[   963.513] (EE) 3: /lib/x86_64-linux-gnu/libc.so.6 (0x7fc673767000+0x83f74) [0x7fc6737eaf74]
[   963.513] (EE) 4: /usr/lib/xorg/modules/libshadow.so (shadowUpdatePacked+0x1da) [0x7fc6690dab7a]
[   963.513] (EE) 5: /usr/lib/xorg/modules/drivers/modesetting_drv.so (0x7fc66f454000+0x8ecb) [0x7fc66f45cecb]
[   963.513] (EE) 6: /usr/lib/xorg/modules/libshadow.so (0x7fc6690d8000+0x15a9) [0x7fc6690d95a9]
[   963.513] (EE) 7: /usr/lib/xorg/modules/libshadow.so (0x7fc6690d8000+0x1624) [0x7fc6690d9624]
[   963.513] (EE) 8: /usr/lib/xorg/modules/drivers/modesetting_drv.so (0x7fc66f454000+0xa113) [0x7fc66f45e113]
[   963.513] (EE) 9: /usr/lib/xorg/modules/drivers/modesetting_drv.so (0x7fc66f454000+0xa3aa) [0x7fc66f45e3aa]
[   963.513] (EE) 10: /usr/lib/xorg/Xorg (BlockHandler+0xb1) [0x5566a8a240d1]
[   963.513] (EE) 11: /usr/lib/xorg/Xorg (WaitForSomething+0x141) [0x5566a8b81f01]
[   963.513] (EE) 12: /usr/lib/xorg/Xorg (0x5566a89cb000+0x5445a) [0x5566a8a1f45a]
[   963.513] (EE) 13: /usr/lib/xorg/Xorg (0x5566a89cb000+0x586a8) [0x5566a8a236a8]
[   963.513] (EE) 14: /lib/x86_64-linux-gnu/libc.so.6 (__libc_start_main+0xf1) [0x7fc6737872e1]
[   963.513] (EE) 15: /usr/lib/xorg/Xorg (_start+0x2a) [0x5566a8a0d33a]
[   963.513] (EE) 
[   963.513] (EE) Bus error at address 0x7fc6548a4000

Note: I installed package xserver-xorg-video-nouveau-dbg 1:1.0.13-3,
but this did not help in making above errors more informative.

While in a working Xorg.0.log there is instead a message:

[    61.898] (II) modeset(0): Allocate new frame buffer 6480x3840 stride
[    62.021] (II) modeset(0): Disabling kernel dirty updates, not required.
[   224.753] (II) modeset(0): EDID vendor "DEL", prod id 53380
[   224.754] (II) modeset(0): Using EDID range info for horizontal sync
[   224.754] (II) modeset(0): Using EDID range info for vertical refresh
[   224.754] (II) modeset(0): Printing DDC gathered Modelines:
[   224.754] (II) modeset(0): Modeline "3840x2160"x0.0  533.25  3840 3888 3920 4000  2160 2163 2168 2222 +hsync -vsync (133.3 kHz eP)


So evidently nouveau cannot allocate another framebuffer with size 6480x3840 


I am using devuan ascii with latest linux kernel 4.20.3, which I have just compiled using these commands:

cd /home/deb/linux-image
unxz -c linux-4.20.3.tar.xz | gpg --verify linux-4.20.3.tar.sign -
unp ./linux-4.20.3.tar.xz
cd linux-4.20.3
cp /boot/config-`uname -r` ./.config
make menuconfig
time fakeroot make-kpkg --initrd --append-to-version=-absurd.2 kernel_image kernel_headers -j40


I will be happy to provide more information, just tell me what you need.

can you help me?
-- 
# Janek Kozicki