UDL device cannot get its own screen

[Ilia Mirkin]

On Wed, Nov 13, 2019 at 11:59 AM Böszörményi Zoltán <zboszor at pr.hu> wrote:
>
> 2019. 11. 12. 17:41 keltezéssel, Ilia Mirkin írta:
> > 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.
>
> I created a merge request that finally made it possible what I wanted.
>
> https://gitlab.freedesktop.org/xorg/xserver/merge_requests/334
>
> Now, no matter if I use the intel or modesetting drivers for the
> Device sections using the Intel heads, or AutoBindGPU set to true or
> false, the UDL device is correctly matched with its Option "kmsdev"
> setting to the plaform device's device path.
>
> This patch seems to be a slight layering violation, but since the
> modesetting driver is built into the Xorg server sources, the patch
> may get away with it.

Have you looked at setting AutoAddGPU to false? AutoBindGPU is too
late -- that's when you already have a GPU, whether to bind it to the
primary device (/screen/whatever). You need to not have a GPU in the
first place.

  -ilia