UDL device cannot get its own screen

[Ilia Mirkin]

On Tue, Nov 12, 2019 at 9:23 AM Böszörményi Zoltán <zboszor at pr.hu> wrote:
> But no, all GPU devices (now only one, the UDL device) have screen 0
> (a.k.a. DISPLAY=:0.0) set when AutoBindGPU is true:
>
> [  2444.576] xf86AutoConfigOutputDevices: xf86NumScreens 2 xf86NumGPUScreens 1
> [  2444.576] xf86AutoConfigOutputDevices: GPU #0 driver 'modesetting' 'modeset' scrnIndex
> 256 origIndex 257 pScreen->myNum 256 confScreen->screennum 0
> confScreen->device->identifier 'Intel0'
>   confScreen->device->screen 0 confScreen->device->myScreenSection->screennum 0
> confScreen->device->myScreenSection->device->screen 0
>
> Somehow, Option "Device" should ensure that the UDL device is actually
> treated as a framebuffer that can be rendered into (i.e. to be modeset(2)
> instead of modeset(Gn)) and it should be woken up automatically.
>
> This is what AutoBindGPU is supposed to do, isn't it?
>
> But instead of assigning to screen 0, it should be assigned to whatever
> screen number it is configured as.
>
> I know it's not a common use case nowadays, but I really want separate
> fullscreen apps on their independent screens, including a standalone UDL
> device, instead of having the latters as a Xinerama extension to some
> other device.

If you see a "G", that means it's being treated as a GPU device, which
is *not* what you want if you want separate screens. You need to try
to convince things to *not* set the devices up as GPU devices, but
instead put each device (and each one of its heads, via ZaphodHeads)
no a separate device, which in turn will have a separate screen.

  -ilia