On Tue, Mar 26, 2013 at 04:13:13PM +0100, Daniel Vetter wrote:
On Tue, Mar 26, 2013 at 12:48:45PM +0100, Danny Baumann wrote:
When controlling backlight devices via sysfs interface, user space generally assumes the minimum level (0) still providing a brightness that is usable by the user (probably due to the most commonly used backlight device, acpi_videoX, behaving exactly like that). This doesn't match the current behaviour of the intel_backlight control, though, as the value 0 means 'backlight off'.
In order to make intel_backlight consistent to other backlight devices, introduce a module parameter that allows shifting the 0 level of the intel_backlight device. It's expressed in percentages of the maximum level. The default is 5, which provides a backlight level that is barely readable. Setting it to 0 restores the old behaviour.
Signed-off-by: Danny Baumann dannybaumann@web.de
Thus far our assumption always was that the acpi backlight works better than the intel native backlight. So everything only uses the intel backlight if there's no other backlight driver by default.
There are machines, such as the pnv netbook on my desk, on which intel_backlight does nothing and the only control is through acpi_backlight0. Generalising expected behaviour based on one firmware implementation is fraught with danger. -Chris