Linux: How to find the device driver used for a device?

Just use /sys.

Example. I want to find the driver for my Ethernet card:

$ sudo lspci
...
02:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168B PCI Express Gigabit Ethernet controller (rev 01)
$ find /sys | grep drivers.*02:00
/sys/bus/pci/drivers/r8169/0000:02:00.0

That is r8169.

First I need to find coordinates of the device using lspci; then I find driver that is used for the devices with these coordinates.

Here's a little script I wrote:

#!/bin/bash
for f in /sys/class/net/*; do
    dev=$(basename $f)
    driver=$(readlink $f/device/driver/module)
    if [ $driver ]; then
        driver=$(basename $driver)
    fi
    addr=$(cat $f/address)
    operstate=$(cat $f/operstate)
    printf "%10s [%s]: %10s (%s)\n" "$dev" "$addr" "$driver" "$operstate"
done

Sample output:

$ ~/what_eth_drivers.sh 
      eth0 [52:54:00:aa:bb:cc]: virtio_net (up)
      eth1 [52:54:00:dd:ee:ff]: virtio_net (up)
      eth2 [52:54:00:99:88:77]: virtio_net (up)
        lo [00:00:00:00:00:00]:            (unknown)

sudo lspci -v will show it. like this:

$ sudo lspci -v
00:01.0 VGA compatible controller: Advanced Micro  Devices, Inc......
...
Kernel driver in use: radeon
Kernel modules: radeon

You can also combine it with grep like this:

$ sudo lspci -v | grep -A 20 VGA