Existem algumas coisas para tentar neste AskUbuntu Q & A intitulado: Como posso consertar drivers i915 quebrados para GPUs Intel? .
Em pesquisando essa questão , parece que a resposta é não, não há uma maneira de ativar i915 sem ACPI.
trecho
On Mon, Sep 09, 2013 at 04:42:20PM +0800, Aaron Lu wrote:
According to Matthew Garrett, "Windows 8 leaves backlight control up to individual graphics drivers rather than making ACPI calls itself. There's plenty of evidence to suggest that the Intel driver for Windows [8] doesn't use the ACPI interface, including the fact that it's broken on a bunch of machines when the OS claims to support Windows 8. The simplest thing to do appears to be to disable the ACPI backlight interface on these systems".
There's a problem with that approach, however, because simply avoiding to register the ACPI backlight interface if the firmware calls _OSI for Windows 8 may not work in the following situations: (1) The ACPI backlight interface actually works on the given system and the i915 driver is not loaded (e.g. another graphics driver is used). (2) The ACPI backlight interface doesn't work on the given system, but there is a vendor platform driver that will register its own, equally broken, backlight interface if not prevented from doing so by the ACPI subsystem. Therefore we need to allow the ACPI backlight interface to be registered until the i915 driver is loaded which then will unregister it if the firmware has called _OSI for Windows 8 (or will register the ACPI video driver without backlight support if not already present).
Então, parece que os dois estão ligados.