Question about hotplugging

[Mark van Rossum]

On my laptop I use Xorg with the intel driver on Debian.

When I hotplug my 2560x1600 monitor, the desktop switches to that monitor.
When I hotplug my 2560x1440 monitor, the desktop gets extended.


Logs:
Xorg (==) intel(0): Display hotplug detection enabled
....
/usr/lib/gdm3/gdm-x-session: (II) intel(0): resizing framebuffer to 
2560x1600
/usr/lib/gdm3/gdm-x-session[2975]: (II) intel(0): switch to mode 
2560x1600 at 59.9 on DP1 using pipe 0, position (0, 0), rotation normal, 
reflection none

However, when I plug in a 2560x1440:
gdm-x-session[1788]: (II) intel(0): resizing framebuffer to 4480x1440
gdm-x-session[1788]: (II) intel(0): switch to mode 2560x1440 at 60.0 on DP1 
using pipe 1, position (1920, 0), rotation normal, reflection none

This latter behaviour is not desired as it leads to occasional crashed.


Question:
- who does the mode-switching? (Xorg, driver, xinerama, gdm?)

- how can I change the behaviour, so that when I hotplug the 2560x1440 
monitor, the framebuffer becomes 2560x1440 and not 4480x1440

Thanks,



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