Tried on both 5.17 and 5.20, Debian and Ubuntu with legacy kernel. Debian has systemd 215, Ubuntu has 225 iirc.
If I plug an iphone usbmuxd is started by systemd-udevd as directed by udev rule (stock one) and gets shut down when I unplug it, again how it's supposed to be. The problem is, it does not start if I plug any Apple device again. Restarting systemd-udevd service does not help at all, and when I reboot the board usbmuxd gets started when I plug iphone but again only once.
1st plug in/plug off in syslog:
Sep 19 09:26:57 localhost kernel: [ 90.005422] ehci_irq: port change detect Sep 19 09:26:57 localhost kernel: [ 90.279798] usb 2-1: new high-speed USB device number 2 using sw-ehci Sep 19 09:26:57 localhost systemd[1]: Started Socket daemon for the usbmux protocol used by Apple devices. Sep 19 09:26:57 localhost usbmuxd[1070]: [09:26:57.922][3] usbmuxd v1.1.0 starting up Sep 19 09:26:57 localhost usbmuxd[1070]: [09:26:57.928][3] Successfully dropped privileges to 'usbmux' Sep 19 09:26:57 localhost usbmuxd[1070]: [09:26:57.945][3] Could not get old configuration descriptor for device 2-2: -5 Sep 19 09:26:57 localhost usbmuxd[1070]: [09:26:57.949][3] Connecting to new device on location 0x20002 as ID 1 Sep 19 09:26:57 localhost usbmuxd[1070]: [09:26:57.950][3] Initialization complete Sep 19 09:26:57 localhost usbmuxd[1070]: [09:26:57.950][3] Enabled exit on SIGUSR1 if no devices are attached. Start a new instance with "--exit" to trigger. Sep 19 09:26:57 localhost usbmuxd[1070]: [09:26:57.950][3] Connected to v2.0 device 1 on location 0x20002 with serial number 4d97a270aba9ba766a13989d9a90caa806d31b6b Sep 19 09:26:58 localhost kernel: [ 90.768031] ipheth 2-1:4.2: Apple iPhone USB Ethernet device attached Sep 19 09:26:58 localhost kernel: [ 90.775448] usbcore: registered new interface driver ipheth
Sep 19 09:28:27 localhost kernel: [ 180.016143] ehci_irq: port change detect Sep 19 09:28:27 localhost kernel: [ 180.020243] usb 2-1: USB disconnect, device number 2 Sep 19 09:28:27 localhost usbmuxd[1070]: [09:28:27.212][3] Removed device 1 on location 0x20002 Sep 19 09:28:27 localhost kernel: [ 180.077995] ipheth 2-1:4.2: Apple iPhone USB Ethernet now disconnected Sep 19 09:28:27 localhost usbmuxd[1070]: [09:28:27.275][3] usbmuxd shutting down Sep 19 09:28:27 localhost usbmuxd[1070]: [09:28:27.376][3] Shutdown complete
Then the same device plugged in:
Sep 19 09:29:31 localhost kernel: [ 244.610407] ehci_irq: port change detect Sep 19 09:29:32 localhost kernel: [ 244.878100] usb 2-1: new high-speed USB device number 3 using sw-ehci
And that's all.
This works on amd64 Ubuntu 16.04 as expected.
EDIT: usbmuxd is properly started by systemd-udevd on Jessie vanilla, so this seems related to kernel.
EDIT2: board is Banana Pro.