Linux support

[haimgel]

Some preliminary Linux support

Things that seem to be working

The app detected USB changes and changed display inputs based on that. I tested this on Raspberry Pi 3, don't have a normal Linux desktop.

Things that do not work / missing

• "Wake up display before switching" functionality is not implemented.
• Documentation: DDC on Linux seems to be more finicky, I had to add my user to the i2c group for the app to work.
• Config file location does not make much sense, should also check in /etc/
• Log file location does not make sense either, should just log to syslog.
• Should package this as .deb or .rpm and include a Systemd wrapper ideally.

Ref: #22

[universal]

trying this out under ubuntu 20.04/popos, and for now:

• needs libudev-dev package on linux
  • need to create `~/.config/display-switch.ini
  • no i2c group on ubuntu 20.04/popos -> sudo chown `whoami` /dev/i2c-10 (for me, used ddcontrol -p to figure out i2c device)

switching usb device away and back to this machine:

11:23:26 [INFO] Display '22794' #0 is currently set to 0xf
11:23:35 [DEBUG] (1) display_switch::app: Detected device change. Removed device: "0bda:0411"
11:23:35 [DEBUG] (1) display_switch::app: Detected device change. Removed device: "045e:082a"
11:23:35 [DEBUG] (1) display_switch::app: Detected device change. Removed device: "046d:0891"
11:23:36 [DEBUG] (1) display_switch::app: Detected device change. Removed device: "046d:c33c"
11:23:36 [DEBUG] (1) display_switch::app: Detected device change. Removed device: "0bda:5411"
11:23:43 [DEBUG] (1) display_switch::app: Detected device change. Added device: "0bda:5411"
11:23:44 [DEBUG] (1) display_switch::app: Detected device change. Added device: "0bda:0411"
11:23:45 [DEBUG] (1) display_switch::app: Detected device change. Added device: "045e:082a"
11:23:45 [DEBUG] (1) display_switch::app: Detected device change. Added device: "046d:0891"
11:23:45 [DEBUG] (1) display_switch::app: Detected device change. Added device: "046d:c33c"
11:23:45 [INFO] Detected device we're looking for "046d:c33c"
11:23:45 [DEBUG] (1) display_switch::platform::display_control_ddc_hi: Setting display ''22794' #0' to 0xf
11:23:45 [INFO] Display '22794' #0 set to 0xf

looks good and works for me just fine, as I've only one display directly connected and the other is daisy-chained via displayport :-)

[haimgel]

@universal thanks for testing! Did you happen to notice the permissions / ownership of /dev/i2c-* before you changed it?

We'll need a more permanent solution as this chown is not going to survive a reboot.

[universal]

yep, should be root:root . there are guides for creating udev rules and adding a new usergroup that would provide a more permanent solution. I have been busy with other stuff, but I will crosscheck if it stays across a reboot. I suspect kernel-updates potentially also change the device, but will check that as well.

[universal]

so I just checked:

• owner is root:root
• changing owner does not persist (as predicted/expected)
• ubuntu/popos don't appear to have a dedicated i2c group by default
• https://lexruee.ch/setting-i2c-permissions-for-non-root-users.html -- this appears to be a straightforward guide to adding such a group
• otherwise: the startup script might take care of the chown, not sure about the sudo powers required/possibility of limiting access... but might be fine for a local, single user install :-)

[haimgel]

@universal thanks for checking, makes sense!

I think going forward, the best approach would be building a deb / rpm package to install the app system-wide, with the config in /etc, logging to system logs normally and running under root with systemd. This would sidestep the whole permissions issue completely.

I created #26, #27, #28, that all together should make Linux support more decent, but this PR seems to work good enough for now, will merge it.

[tdryer]

ubuntu/popos don't appear to have a dedicated i2c group by default

You can get an i2c group on Ubuntu by installing the i2c-tools package, which comes with a udev rule.

Then you just need to add your user to the group, and log out for it to take effect:

sudo usermod $USER -aG i2c