BIOSアップデート後の明るさ制御が機能しない

私はThinkpad X220でDebian Jessieを実行しています。昨日、私のラップトップで新しいBIOSを更新した後、Debianの明るさキーが機能しなくなりました。ただし、BIOSの起動中に明るさを変更できます。

私は少し奇妙に聞こえます。どんなアイデアがありますか？

修正する

デフォルトでは、明るさ調整が無効になっているようです。関連出力は次のとおりです。dmesg

[    2.016833] systemd[1]: 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.