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Ghost device connected to Z32 built-in USB hub causing automatic wake from suspend in Linux

HP Recommended
Z32
Linux

When my HP Z32 monitor is connected to my HP EliteBook 820 G4 using the USB-C/USB-C cable provided with the monitor, the Linux kernel running on the laptop sees a "ghost" device connected to the monitor's internal USB hub. This happens even if there is no devices connected to the external downstream USB ports on the monitor.

 

The Linux kernel spends about 15 seconds attempting to enable the device after power-on or resume from suspend, while it logs the following:

 

10:15:14 kernel: usb usb2-port3: Cannot enable. Maybe the USB cable is bad?
10:15:18 kernel: usb usb2-port3: Cannot enable. Maybe the USB cable is bad?
10:15:22 kernel: usb usb2-port3: Cannot enable. Maybe the USB cable is bad?
10:15:22 kernel: usb usb2-port3: attempt power cycle
10:15:26 kernel: usb usb2-port3: Cannot enable. Maybe the USB cable is bad?
10:15:31 kernel: usb usb2-port3: Cannot enable. Maybe the USB cable is bad?
10:15:31 kernel: usb usb2-port3: unable to enumerate USB device

 

At this point, it gives up. Apart from this, the USB hub appears to function correctly - I can plug in peripherals etc. into the monitor's downstream ports and they are all available to the laptop.

 

However, this issue appears to cause the laptop to automatically wake up from suspend. That is, if I suspend it while it is connected to the monitor, it will ostensibly to go to sleep as expected, but wake back up again within a second or two. (The Wake on USB setting in the BIOS setup makes no difference.)

 

In order to make the suspend operation "stick", I need to suspend it again within 15 seconds of the automatic wake-up, i.e., before the unable to enumerate USB device message appears in the logs.

 

If on the other hand the laptop is suspended after it has spent more than 15 seconds awake, i.e., after the unable to enumerate USB device message has appeared, it will not stay suspended.

 

If I instead connect the monitor's upstream USB-C port to a USB-A port on the laptop, using the USB-A/USB-C cable included with the monitor, the log message do not appear and the laptop can be reliably suspended. For now, that is an acceptable workaround for me.

 

However, as I do plan on investing in a new laptop in order to use display output and charging via USB-C, I am worried that this bug will render me unable to reliably suspend.

 

For the record, both the monitor and the laptop are fully up to date with regards to firmware versions and so forth.

 

Anyone else seeing the same issue?

 

For what it is worth, I also wrote a blog post about this issue.

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