[linux] Controlling a USB power supply (on/off) with Linux

The reason why folks post questions such as this is due to the dreaded- indeed "EVIL"- USB Auto-Suspend "feature".

Auto suspend winds-down the power to an "idle" USB device and unless the device's driver supports this feature correctly, the device can become uncontactable. So powering a USB port on/off is a symptom of the problem, not the problem in itself.

I'll show you how to GLOBALLY disable auto-suspend, negating the need to manually toggle the USB ports on & off:

Short Answer:

You do NOT need to edit "autosuspend_delay_ms" individually: USB autosuspend can be disabled globally and PERSISTENTLY using the following commands:

sed -i 's/GRUB_CMDLINE_LINUX_DEFAULT="/&usbcore.autosuspend=-1 /' /etc/default/grub

update-grub

systemctl reboot

An Ubuntu 18.04 screen-grab follows at the end of the "Long Answer" illustrating how my results were achieved.

Long Answer:

It's true that the USB Power Management Kernel Documentation states autosuspend is to be deprecated and in in its' place "autosuspend_delay_ms" used to disable USB autosuspend:

"In 2.6.38 the "autosuspend" file will be deprecated
and replaced by the "autosuspend_delay_ms" file."

HOWEVER my testing reveals that setting usbcore.autosuspend=-1 in /etc/default/grub as below can be used as a GLOBAL toggle for USB autosuspend functionality- you do NOT need to edit individual "autosuspend_delay_ms" files.

The same document linked above states a value of "0" is ENABLED and a negative value is DISABLED:

power/autosuspend_delay_ms

    <snip> 0 means to autosuspend
    as soon as the device becomes idle, and negative
    values mean never to autosuspend.  You can write a
    number to the file to change the autosuspend
    idle-delay time.

In the annotated Ubuntu 18.04 screen-grab below illustrating how my results were achieved (and reproducible), please remark the default is "0" (enabled) in autosuspend_delay_ms.

Then note that after ONLY setting usbcore.autosuspend=-1 in Grub, these values are now negative (disabled) after reboot. This will save me the bother of editing individual values and can now script disabling USB autosuspend.

screengrab: autosuspend values Before and after globally editing

Hope this makes disabling USB autosuspend a little easier and more scriptable-