Question: Device not recognized when connected without a hub. Why?

Hi

I stumbled over a behaviour when connecting a USB device which I couldn't find any explanation for. So, I'm trying here.
Why connecting a USB device (USB-TTL converter) direct and via an USB hub makes a difference? When I connect it directly all I see in /var/log/syslog are errors, when connectedd via a USB-hub it works as expected.
See logs below.
hp8300 is HP Compaq Elite 8300 SFF (QV996AV), kernel: 4.15.0-50-generic #54-Ubuntu

lshw reports:
*-usb:0
description: USB controller
product: 7 Series/C210 Series Chipset Family USB xHCI Host Controller
vendor: Intel Corporation
*-usb:1
description: USB controller
product: 7 Series/C216 Chipset Family USB Enhanced Host Controller #2
vendor: Intel Corporation

BTW, it does work as expected on a Lenovo x220 (same OS). Let me know if I should provide any more information.

Thanks in advance for any hint.

Regards,
Chris

Connected directly:

Jun  4 23:26:44 hp8300 kernel: [218215.233450] usb 1-1.1: new full-speed USB device number 34 using ehci-pci
Jun  4 23:26:44 hp8300 kernel: [218215.313423] usb 1-1.1: device descriptor read/64, error -32
Jun  4 23:26:44 hp8300 kernel: [218215.501445] usb 1-1.1: device descriptor read/64, error -32
Jun  4 23:26:44 hp8300 kernel: [218215.689444] usb 1-1.1: new full-speed USB device number 35 using ehci-pci
Jun  4 23:26:44 hp8300 kernel: [218215.769443] usb 1-1.1: device descriptor read/64, error -32
Jun  4 23:26:44 hp8300 kernel: [218215.957429] usb 1-1.1: device descriptor read/64, error -32
Jun  4 23:26:44 hp8300 kernel: [218216.065626] usb 1-1-port1: attempt power cycle
Jun  4 23:26:45 hp8300 kernel: [218216.669420] usb 1-1.1: new full-speed USB device number 36 using ehci-pci
Jun  4 23:26:45 hp8300 kernel: [218217.085412] usb 1-1.1: device not accepting address 36, error -32
Jun  4 23:26:45 hp8300 kernel: [218217.165414] usb 1-1.1: new full-speed USB device number 37 using ehci-pci
Jun  4 23:26:46 hp8300 kernel: [218217.581413] usb 1-1.1: device not accepting address 37, error -32
Jun  4 23:26:46 hp8300 kernel: [218217.581574] usb 1-1-port1: unable to enumerate USB device

Connected via a simple USB hub:

Jun  4 23:28:08 hp8300 kernel: [218300.044754] usb 1-1.1: new full-speed USB device number 38 using ehci-pci
Jun  4 23:28:08 hp8300 kernel: [218300.161948] usb 1-1.1: New USB device found, idVendor=058f, idProduct=9254
Jun  4 23:28:08 hp8300 kernel: [218300.161950] usb 1-1.1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
Jun  4 23:28:08 hp8300 kernel: [218300.161951] usb 1-1.1: Product: Generic USB Hub
Jun  4 23:28:08 hp8300 kernel: [218300.161952] usb 1-1.1: Manufacturer: ALCOR
Jun  4 23:28:08 hp8300 kernel: [218300.162269] hub 1-1.1:1.0: USB hub found
Jun  4 23:28:08 hp8300 kernel: [218300.162936] hub 1-1.1:1.0: 4 ports detected
Jun  4 23:28:08 hp8300 upowerd[2750]: unhandled action 'bind' on /sys/devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.1/1-1.1:1.0
Jun  4 23:28:08 hp8300 upowerd[2750]: unhandled action 'bind' on /sys/devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.1
Jun  4 23:28:09 hp8300 kernel: [218300.448772] usb 1-1.1.1: new full-speed USB device number 39 using ehci-pci
Jun  4 23:28:09 hp8300 kernel: [218300.557969] usb 1-1.1.1: New USB device found, idVendor=1a86, idProduct=7523
Jun  4 23:28:09 hp8300 kernel: [218300.557973] usb 1-1.1.1: New USB device strings: Mfr=0, Product=2, SerialNumber=0
Jun  4 23:28:09 hp8300 kernel: [218300.557975] usb 1-1.1.1: Product: USB2.0-Serial
Jun  4 23:28:09 hp8300 mtp-probe: checking bus 1, device 39: "/sys/devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.1/1-1.1.1"
Jun  4 23:28:09 hp8300 mtp-probe: bus: 1, device: 39 was not an MTP device
Jun  4 23:28:09 hp8300 kernel: [218300.590591] usbcore: registered new interface driver ch341
Jun  4 23:28:09 hp8300 kernel: [218300.590602] usbserial: USB Serial support registered for ch341-uart
Jun  4 23:28:09 hp8300 kernel: [218300.590614] ch341 1-1.1.1:1.0: ch341-uart converter detected
Jun  4 23:28:09 hp8300 kernel: [218300.591377] usb 1-1.1.1: ch341-uart converter now attached to ttyUSB0

No idea. It sounds like some sort of low-level electrical incompatibility.

Alan Stern