Use sysfs to restart failed PCI devices (WiFi cards, sound cards, etc.)

This article describes one method of restarting PCI devices. It demonstrates restarting a wireless device. But the concept should work on any device whose device driver has adequate hotplug support.^[1]

Computers typically consist of several interconnected devices. Some devices can be physically disconnected and reconnected with ease (for example, most USB devices). Others might require a specific interaction with the operating system or specific software. And others will require a full reboot.

Built-in laptop wireless cards are PCI devices that could fail at runtime but might not be easy to physically disconnect and reconnect without a full reboot. In many cases these devices can be restarted through Linux’s sysfs interface without having to do a full reboot of the computer.

This article will specifically demo how to restart an Atheros wireless card which has locked up.

How to restart PCI devices

Depending on your particular desktop environment and hardware, it may be possible to switch the PCI card off and back on using a GUI or hardware switch or button. But if none of those options exist or work, the following CLI method of restarting the PCI card might prove useful.

To restart a wireless card you will need its PCI domain, bus, device and function address. Run the lspci command, as shown below, and search its output to find your wireless card’s PCI address.

$ lspci
<snip>
3d:00.0 Network controller: Qualcomm Atheros QCA6174 802.11ac Wireless Network Adapter (rev 32)

In the above example, the PCI address of the Atheros card is 3d:00.0. If the address shown does not include a domain part (that is, the number at the start of the line contains only one colon character), then the computer has only one PCI domain and it is 0000.

The following commands, with the capital letters substituted with the device’s PCI address, can be used to restart a PCI device on a running system.^[2]

# echo "1" > /sys/bus/pci/devices/DDDD\:BB\:DD.F/remove  
# sleep 1  
# echo "1" > /sys/bus/pci/rescan

In the above example, the placeholders DDDD, BB, DD, and F are for the PCI device domain, bus, device, and function respectively.

Substituting the values from the example output of the lspci command shown above gives the command that would need to be run to restart the Atheros wireless card on this example system.

$ sudo /bin/sh -c "echo '1' > /sys/bus/pci/devices/0000\:3d\:00.0/remove"
$ sleep 1
$ sudo /bin/sh -c "echo '1' > /sys/bus/pci/rescan"

If required, the above commands could be automated by putting them in a script.

$ nano restart-wireless-card.sh
#!/bin/bash
echo "1" > /sys/bus/pci/devices/0000\:3d\:00.0/remove  
sleep 1  
echo "1" > /sys/bus/pci/rescan

Enable executable permissions with, for example, chmod +x restart-wireless-card.sh and run sudo ./restart-wireless-card.sh whenever you need to restart your PCI device.

Final notes

Not all PCI devices can be restarted using this method. But the real-life example demonstrated above does work to get the WiFi card running again without requiring a full reboot of the PC.

References

1. stackexchange.com: Does PCIe hotplug actually work in practice?
2. stackexchange.com: How to Reset/Cycle Power to a PCIe Device?