https://bugs.freedesktop.org/show_bug.cgi?id=41265
--- Comment #37 from gyhor@gmx.de 2012-08-16 10:08:23 UTC --- I am not sure. In function radeon_atpx_pci_probe_handle() do get the DEVICE_ACPI_HANDLE:
dhandle = DEVICE_ACPI_HANDLE(&pdev->dev);
It fails with status = acpi_get_handle(dhandle, "ATPX", &atpx_handle);
btw it is kernel 3.5RC7