However, the screen brightness controls did not work. Some online research suggested adding
acpi_osi=Linux to the kernel boot parameters and I also found a tip in the thinkpad-acpi driver documentation for how to force-enable it (over the native Linux ACPI driver).
First, edit your
/etc/default/grub file to add
acpi_backlight=vendor arguments to
GRUB_CMDLINE_LINUX_DEFAULT. It should look something like this:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi=Linux acpi_backlight=vendor"
sudo update-grub to enable the new arguments. After a reboot, my brightness controls were working.
The other thing I noted was a strange error on boot: “failed to get i915 symbols”. I found a solution for that, too:
sudo -s echo "i915" >> /etc/initramfs-tools/modules update-initramfs -k all -u reboot
For more general information about Linux on the Thinkpad X201, see ThinkWiki.