On Wed, 15 Jul 2009, Zhang Rui wrote: > Only one ACPI video bus device for a VGA controller. > > Some buggy BIOS exports multiple ACPI video bus devices for the same > VGA controller, and multiple backlight control methods as well. > This messes up the ACPI video backlight control. > http://bugzilla.kernel.org/show_bug.cgi?id=13577 > > With this patch applied, only the first ACPI video bus device > under a PCI device node is bind to ACPI video driver. > > The questions is that, we never notice this kind of devices before, > thus I'm not sure this won't break any laptops. Laptops often have more than one video bus device, and you _have_ to choose the one that is _active_ (which might not be the first one you find). This is done on laptops that can have either discrete or in-chipset graphics, for example. I have seen it in several thinkpad models. There is also the new class of laptops that have *both* discrete and in-chipset GPUs and can switch them at runtime (well, Linux can't cope with it yet and ends up requiring the switch to be done in BIOS setup screen, AFAIK, but I hope that changes someday). I never looked at the DSDT of one of these to know how it looks like, but it would make sense that the ACPI video driver would have to be able to bind to more than one display device, and drive them separately, and do the right thing when the device is hotplugged/hotunplugged (or activated/deactivated)... -- "One disk to rule them all, One disk to find them. One disk to bring them all and in the darkness grind them. In the Land of Redmond where the shadows lie." -- The Silicon Valley Tarot Henrique Holschuh -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
