I am running Debian Jessie on my Thinkpad X220. Yesterday, after flashing a new BIOS on the laptop, the brightness keys stopped working on Debian. I can change the brightness during the BIOS bootup though.
Sounds kinda strange to me. Any ideas?
It looks like the brightness controls are disabled by default. Here is the relevant output from
[ 2.016833] systemd: Set hostname to <thinkpad-x220>. [ 2.192092] thinkpad_acpi: ThinkPad ACPI Extras v0.25 [ 2.192171] thinkpad_acpi: http://ibm-acpi.sf.net/ [ 2.192258] thinkpad_acpi: ThinkPad BIOS 8DET69WW (1.39 ), EC unknown [ 2.192331] thinkpad_acpi: Lenovo ThinkPad X220, model 4291Y3H [ 2.193207] thinkpad_acpi: detected a 16-level brightness capable ThinkPad [ 2.200276] thinkpad_acpi: radio switch found; radios are enabled [ 2.200401] thinkpad_acpi: possible tablet mode switch found; ThinkPad in laptop mode [ 2.200496] thinkpad_acpi: This ThinkPad has standard ACPI backlight brightness control, supported by the ACPI video driver [ 2.200496] thinkpad_acpi: Disabling thinkpad-acpi brightness events by default... [ 2.202578] thinkpad_acpi: rfkill switch tpacpi_bluetooth_sw: radio is unblocked [ 2.203332] thinkpad_acpi: Standard ACPI backlight interface available, not loading native one [ 2.203637] thinkpad_acpi: Console audio control enabled, mode: monitor (read only) [ 2.205397] input: ThinkPad Extra Buttons as /devices/platform/thinkpad_acpi/input/input5 [ 2.305667] thinkpad_ec: thinkpad_ec 0.41 loaded.