On Tue, Mar 26, 2013 at 06:10:30PM +0100, Danny Baumann wrote:
Am 26.03.2013 18:02, schrieb Matthew Garrett:
I'm not quite clear what you mean here. The behaviour of "0" isn't well defined for the ACPI backlight driver - it's perfectly reasonable for it to turn the backlight off entirely. Anything assuming that "0" is still visible is broken.
Well, the ACPI spec says this (section B.5.2):
" The OEM may define the number 0 as "Zero brightness" that can mean to turn off the lighting (e.g. LCD panel backlight) in the device. This may be useful in the case of an output device that can still be viewed using only ambient light, for example, a transflective LCD. "
My interpretation of this is that the value 0 is supposed to still be visible. I'm pretty sure I saw a statement that 0 is supposed to mean "barely visible" somewhere, but can't find it at the moment. I'll search for the source of it.
I think that's a stretch - "This may be useful" isn't normative language, "The OEM may define" is. But even if we do assert it for the ACPI backlight, it's not true for other interfaces - zero backlight intensity is supposed to be screen off on Apple hardware, for instance.