PowerTOP and USB Autosuspend

Some of this was touched on at Fedora on Macbook.

PowerTOP is a useful tool to get more battery life out of a laptop. It makes the difference of several hours of battery life, so it's a useful thing to install.

PowerTOP

Install and enable it:

sudo dnf install powertop
sudo systemctl enable powertop.service
sudo systemctl start powertop.service

The service runs powertop --auto-tune which automatically sets most tunables to their "Good" state, for maximum battery life.

But sometimes it doesn't work well, especially with USB mice.

USB Autosuspend

It perplexed me for a while why my USB mouse on a laptop would deactivate itself randomly (its LED turns off, and the mouse doesn't work until you click one of the buttons, and then it will power itself off again after a couple minutes...). Unplugging the USB mouse and plugging it back in would fix the problem and it would no longer auto-suspend itself. I was checking /var/log/messages and all the usual suspects until I realized it was PowerTOP that was the problem.

When powertop --auto-tune gets run, every USB device attached at the time gets the auto power management profile set, meaning they deactivate themselves to save power. On a keyboard or most other devices that's probably fine, but a mouse isn't. My workarounds have been to either not connect my USB devices until after my laptop boots into my desktop environment, or to unplug and replug the USB mouse after the fact.

I can't find a good "official" way to work around the problem. Google suggests editing things in /etc/laptop-mode but that isn't a thing in Fedora, and others have suggested setting up udev rules for your USB device, but that doesn't work either. I even found this Power Management Guide for Fedora 19 which pointed me to powertop2tuned to override powertop rules, but that didn't help me either.

My hacky work-around: make a shell script that starts on user log-in, that undoes PowerTOP's change to the USB device.

1. Run sudo powertop and go to the Tunables tab.
2. Find the entry like "Autosuspend for USB device Microsoft 3-Button Mouse with IntelliEye(TM) [Microsoft]", and toggle it into a "Bad" state (meaning it doesn't auto-suspend now).

3. When toggling it, PowerTOP shows a message of what it did to toggle it, which looks like:

   echo 'on' > '/sys/bus/usb/devices/2-3.2.3.1/power/control'

4. Create a shell script that does that job. I made mine at ~/bin/powertop-fix:

#!/bin/sh

# Disable USB auto-suspend for my mouse on startup
sleep 5;
MOUSE="/sys/bus/usb/devices/2-3.2.3.1/power/control";
if [ -f "$MOUSE" ]; then
	echo 'on' > $MOUSE;
fi

1. Edit your sudoers file to allow running that script with no password:

kirsle  ALL=(ALL) NOPASSWD: /home/kirsle/bin/powertop-fix

1. Make sudo /home/kirsle/bin/powertop-fix start automatically using your desktop's session management settings (e.g. Xfce Sessions and Startup -> Application Autostart).