KB: Using bus powered USB peripherals with the pinephone keyboard mounted

[docsunset]

From megi: https://xnux.eu/pinephone-keyboard/faq.html#safety

Can I plug something to the phone's Type-C port?

No! When the keyboard is connected to the phone, it powers the phone by internally supplying 5V to the VBUS of the phone's Type-C port. So if you connect another USB power supply to the phone's Type-C port, it's like connecting two chargers to the phone by cutting and splicing their cables. (Likely not a good thing, or something you'd consider doing if it was presented to you that way.) If you connect some USB peripheral there that only consumes power from the port (like mouse, unpowered dock, etc.), it may work (in theory), but only if you make *absolutely sure* the phone will not enable its power output to the USB device! No distros ensure that at the moment. When you plug USB periperal it's the same as plugging in two chargers into the same port, without additional software support that doesn't exist, yet.

I'm wondering if anyone knows, or has advice where to ask around, about how to "make *absolutely sure* the phone will not enable its power output to the USB device." Is this something that can be achieved through sysfs? Or a udev rule? Or would it require hacking on the kernel? Has it already been done in any distros?

I've just installed Arch ARM (https://github.com/dreemurrs-embedded/Pine64-Arch) and am hoping to use the pinephone with a teensy 4.1 microcontroller attached via USB along with the keyboard, but I would like to avoid frying either the pinephone, teensy, or keyboard.