I have just bought a new thinkpad r61 laptop, and I have installed gentoo on it. When I load the module "thinkpad_acpi", I get the following in dmesg.
thinkpad_acpi: ThinkPad ACPI Extras v0.19
thinkpad_acpi: ThinkPad BIOS 7LETB6WW (2.16 ), EC 7KHT24WW-1.08
thinkpad_acpi: Lenovo ThinkPad R61
thinkpad_acpi: radio switch found; radios are enabled
thinkpad_acpi: standard ACPI backlight interface available, not loading native one...
input: ThinkPad Extra Buttons as /class/input/input7
But even though it claims to have detected that the standard acpi backlight interface is available, but for some reason the device isn't being created in /proc/acpi/ibm