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i7-8665UE USB Speed Demotion; USB3_PSSEN Register


Hi Everyone,

We're seeing instability in USB 3.0 bus due to improperly routed superspeed lines. USB 2 is very reliable on this same phy.

Attempting to force this behaviour in software is so far unsuccessful.

The USB3_PSSEN register appears to be all 0's which should indicate super speed is disabled on this platform and attempting to set these values has no effect:

sudo setpci -H1 -d 8086:9ded d8.l
sudo setpci -H1 -d 8086:9ded d8.l=0xFFFF
sudo setpci -H1 -d 8086:9ded d8.l

I feel like this is a misread of the documentation here by me. I assumed that by setting USB3_PSSEN register to 0 in the xHCI PCI device I would disable super speed and run all usb ports in usb2 mode (high speed).

Any help would be appreciated to help me disable USB3 on the xHCI controller.

For various product reasons we cannot update the BIOS. We are running a 4.19 + PREEMPT_RT kernel on an Ubuntu16.04 LTS OS. 

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2 Replies

Hi @_actate 


Thanks for your additional information.

USB3 speed is set at BIOS/FW level; so it cannot be changed at OS level.


Best regards,


Jaime L.

Intel Customer Support Engineer

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Hi @Jaime_Lizarme ,

I'm wondering if it were possible to disable usb3 entirely at the OS level so that USB2 can take over - this port works just fine in USB2 mode (even when sysfs authorized field of the USB3 hub is set to 0) however it seems the moment any superspeed pins make contact the xhci driver insists on using USB3.

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