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

[Janek Kozicki]

Hi,

thank you very much for your reply.

I will explain my use case in more detail. First thing is to note that
it worked with nvidia (apart from this annoying system freeze which
happened roughly every three months).


> First off, you're not using the nouveau ddx, you're using the
> modesetting ddx. This isn't a problem in itself, but if you're going
> to report bugs, you should file them against the proper component.

oh, wow. I don't know what is ddx or modesetting ddx. Google tells me
that it is related to intel drivers? But I have nvidia card. And
Xorg.0.log refers to nouveau and nv.

Please provide me some links where I can learn about the difference
between nouveau and ddx.


> Secondly, I'm a bit unclear as to what your setup is. A single X
> server takes over a whole GPU. Recently "leasing" has been introduced
> which enables a drm master to "lease" certain outputs to another
> process, but I haven't played much with it.

I press Ctrl-Alt-F2 to switch to text virtual terminal, there I log
in as user 'research' and type

$ startx -- -nolisten tcp -dpi 100

Thus I start an xserver (owned by user research) which uses three LCD
screens 6480x3840 in multihead configuration. All LCD screens are
part of the same desktop and part of the same xserver.

Then I press Ctrl-Alt-F4 to switch to another text virtual terminal,
there I log in as user 'yade' and type

$ startx -- -nolisten tcp -dpi 100

On nvidia drivers it works and it starts yet another xserver (owned
by user yade) which uses three LCD screens 6480x3840 in multihead
configuration.

The only way to work as former user 'research' is to press Ctrl-Alt-F2
to switch to its xserver.

Then I press Ctrl-Alt-F11 to another text virtual console, there I
log in as another user and start third xserver with the same command:

$ startx -- -nolisten tcp -dpi 100

I am attaching Xorg.0.log from succesfull startup and a (second)
failed startup.

I hope that I explained my use case in an understandable manner?

> If you want different X
> servers for each (or groups of) outputs of a single GPU, then you need
> to get leasing going.

It's not like this. At single time all GPU outputs go to single
xserver. I just switch between xservers by switching virtual
terminals (pressing Ctrl-Alt-F2, then Ctrl-Alt-F4).


> I'm not sure as to your precise use-case, but perhaps another option
> is to have a single X server with multiple X screens. This can be done
> by enabling ZaphodHeads. This was a common way to get a mega-screen
> across multiple GPUs prior to output slaving being introduced, there's
> a guide here https://nouveau.freedesktop.org/wiki/MultiMonitorDesktop/

I am sure that single X server will not work here. Each xserver is
owned by different user. I organized it in this way so that command
"slay yade" will not interfere with my other working X sessions.

I have only one graphics card in my computer, it has three
DisplayPort outputs, and they are connected to my three LCD screens.


> Lastly, note that no matter how many physical outputs there might be,
> Kepler+ only supports 4 CRTC's and earlier gens had 2. That puts a
> hw-imposed upper limit on the number of images that can be produced
> for these outputs.


My graphics card is GeForce GTX 1060 SC 6GB GDDR5 (192 Bit) DVI-D, 3xDP, HDMI

Does it mean that with nouveau driver my use-case will work with only
2 screens or with 4 screens?

Please note that my use-case works perfectly (except the occasional
system freeze roughly every three months) when I use nvidia drivers.


04:00.0 VGA compatible controller: NVIDIA Corporation GP106 [GeForce GTX 1060 6GB] (rev a1) (prog-if 00 [VGA controller])
	Subsystem: eVga.com. Corp. GP106 [GeForce GTX 1060 6GB]
	Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
	Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
	Latency: 0, Cache Line Size: 64 bytes
	Interrupt: pin A routed to IRQ 11
	NUMA node: 0
	Region 0: Memory at de000000 (32-bit, non-prefetchable)
	Region 1: Memory at c0000000 (64-bit, prefetchable)
	Region 3: Memory at d0000000 (64-bit, prefetchable)
	Region 5: I/O ports at 7000
	Expansion ROM at df000000 [disabled]
	Capabilities: <access denied>
	Kernel driver in use: nouveau
	Kernel modules: nouveau



thanks a lot for your help!
Janek Kozicki
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