[systemd-devel] DisplayPort display non-persistent device naming

[Marcin Kocur]

Hello,

this is the output of turning off and on my display (using power button):


[mk at linux ~]$ udevadm  monitor
monitor will print the received events for:
UDEV - the event which udev sends out after rule processing
KERNEL - the kernel uevent

KERNEL[79.909185] change 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0 (drm)
KERNEL[79.909318] remove 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/i2c-3/i2c-dev/i2c-3 (i2c-dev)
KERNEL[79.909385] remove 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/i2c-3 (i2c)
KERNEL[79.909564] remove 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-2/drm_dp_aux1 
(drm_dp_aux_dev)
KERNEL[79.909599] remove 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-2 (drm)
KERNEL[79.909733] remove 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-3/drm_dp_aux2 
(drm_dp_aux_dev)
KERNEL[79.909756] remove 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-3 (drm)
KERNEL[79.909882] change 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0 (drm)
UDEV  [79.912218] remove 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/i2c-3/i2c-dev/i2c-3 (i2c-dev)
UDEV  [79.912301] change 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0 (drm)
UDEV  [79.912708] remove 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/i2c-3 (i2c)
UDEV  [79.913400] remove 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-2/drm_dp_aux1 
(drm_dp_aux_dev)
UDEV  [79.913832] remove 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-3/drm_dp_aux2 
(drm_dp_aux_dev)
UDEV  [79.913875] remove 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-2 (drm)
UDEV  [79.914230] remove 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-3 (drm)
UDEV  [79.914814] change 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0 (drm)
KERNEL[85.337964] add 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/i2c-3/i2c-dev/i2c-3 (i2c-dev)
KERNEL[85.337996] add 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/i2c-3 (i2c)
UDEV  [85.340976] add 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/i2c-3/i2c-dev/i2c-3 (i2c-dev)
UDEV  [85.342384] add 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/i2c-3 (i2c)
KERNEL[85.482056] add 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-3 (drm)
KERNEL[85.482116] add 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-3/drm_dp_aux1 
(drm_dp_aux_dev)
KERNEL[85.482215] change 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0 (drm)
KERNEL[85.482231] add 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-4 (drm)
KERNEL[85.482308] add 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-4/drm_dp_aux2 
(drm_dp_aux_dev)
KERNEL[85.482386] change 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0 (drm)
KERNEL[85.482415] change 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0 (drm)
UDEV  [85.483698] add 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-3 (drm)
UDEV  [85.485053] add 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-3/drm_dp_aux1 
(drm_dp_aux_dev)
UDEV  [85.486553] change 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0 (drm)
UDEV  [85.487973] add 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-4 (drm)
UDEV  [85.489186] add 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0/card0-DP-4/drm_dp_aux2 
(drm_dp_aux_dev)
UDEV  [85.490094] change 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0 (drm)
UDEV  [85.491090] change 
/devices/pci0000:00/0000:00:08.1/0000:08:00.0/drm/card0 (drm)


The monitor was visible in xrandr as DP-2, after power off and on it's 
visible as DP-3 (DP-2 is still there "disconnected").

It's troublesome for:

- GUI display configurators

- scripting

- for Xorg configuration which stops to work:

Section "Monitor"
     Identifier  "DP-2"
     Option      "Primary" "true"
EndSection

Is this a bug or a feature?

-- 
Pozdrawiam / Greetings
Marcin Kocur █