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lainlover

Member

Registered: 2024-04-01

Posts: 19

How to monitor USB-C power delivery

I have a Dell powered USB-C dock which I use to charge my T14, and am looking to use this same dock with my desktop's USB-C ports, for ethernet/kb/mouse. I have tested the connection and it works for my purposes, yet I'm worried the dock could be trying to charge the desktop through the port, inadvertently frying the connection. I have read that in theory this doesn't happen as PD is negotiated between devices but I just can't trust it without some confirmation.
Is there some CLI utility available for monitoring power delivery statistics for USB-C ports? This could be a generic solution for all USB ports more broadly. Particularly, direction of power flow and voltage / current would be very helpful.

impossibleveins23

Member

From: Israel

Registered: 2022-06-18

Posts: 171

Re: How to monitor USB-C power delivery

I'm not sure if it can happen (this mean the motherboard accepts multiple power sources and the USB port need to support PD which in most desktop unnecessary).
You can run udevadm monitor and connect the dock, to check whether it has any effect on power supply.

Even in hypothetical situation where a PC accepts multiple PD, it's up to the host to manage it as anything you'll try to do kernel/userspace may be far too late...

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lainlover

Member

Registered: 2024-04-01

Posts: 19

Re: How to monitor USB-C power delivery

I ran udevadm monitor and diff-ed the logs between using USB-A (via adapter, obviously this doesn't have PD) and USB-C. No visible difference apart from the port identifier in the logs.
No mention of power in either of the logs, so I wonder where that puts me... Is there some kind of protocol analyser utility like wireshark but for USB packets? Since PD has to be negotiated, it should be visible at some point in such an exchange.
Ring any bells?

Last edited by lainlover (2024-05-22 12:06:14)

impossibleveins23

Member

From: Israel

Registered: 2022-06-18

Posts: 171

Re: How to monitor USB-C power delivery

USB PD is implemented on the hardware level. This is why you can charge when your device is powered off for instance.
The manufacturer can expose some interfaces to control the charging.
In your case, the desktop USB probably does not have this capability enabled.

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