[Bug 99103] Same output (DisplayPort) is used in multi-head configuration for different Devices/Displays

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=99103

--- Comment #6 from Alex Deucher <alexdeucher at gmail.com> ---
(In reply to Stefan.LAUTERWASSER from comment #5)
> (In reply to Michel Dänzer from comment #4)
> > In short, this configuration (Zaphod style, with 4 screens per GPU) isn't
> > supported. The radeon driver only supports 2 screens per GPU in Zaphod mode.
> Sorry, I saw the restriction of 6 monitors per GPU and didn't saw any
> restriction of 2 screens per GPU - I may overlooked.

X screens (e.g., :0.0, :0.1) not monitors.  Depending on the asics the hardware
supports up to 6 monitors per GPU.  You can have multiple monitors per X
screen.

> 
> Is the limit simulated or by design? I have an idea of the differences
> supporting one or two, but didn't understand the differences in supporting
> two or six screens - the idea of fragmentation exists already.
> You don't need to explain in details, but if you are able to refer to some
> background information - I am just a bit stupid and nosy.

Zaphod mode is a legacy feature and as Michel said, it only supports two X
screens per GPU.

> 
> > Unless you really need multiple X11 protocol screens and/or static
> > configuration in xorg.conf, I'd suggest trying without xorg.conf and letting
> > the desktop environment manage the display configuration via RandR 1.4. Note
> > that in this case I highly recommend using at least the xf86-video-ati 7.8.0
> > release, possibly even current Git master, and ideally a newer version of
> > Xorg as well.
> We use only X server with openbox - not that rich desktop environment.
> I tried to configure with xrandr command but I have no idea how to create
> displays without xorg.conf and I don't know how to bind a output to a
> display.
> I am able to create displays and output binding with xorg.conf only, can you
> show me a different way/command?
> But if the driver doesn't support more than 2 screens how can xrandr help?
> 

The driver supports up to 6 monitors, but only 2 independent X screens.  With
randr, you have one X screen with up to 6 monitors.

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