On Thu, 2009-01-08 at 11:32 +0800, Matthew Garrett wrote: > On Thu, Jan 08, 2009 at 10:58:16AM +0800, Zhang Rui wrote: > > > Some users used to control the backlight via the platform interface. > > But commit c3d6de698c84efdbdd3781b7058bcc339ab43da8 disables the platform > > backlight control if ACPI video backlight control is available. > > > > This breaks the laptops with buggy _BCL/_BCM/_BQC methods. i.e. only ACPI > > backlight I/F are available on these laptops but they don't work. > > > > With this patch applied, the ACPI backlight control are disabled instead > > on these laptops. > > Why? These all seem to behave consistently, so I can't see any problem > with us simply adding support for this varient. the problem is that the ACPI backlight I/F and the platform I/F coexists before commit c3d6de698c84efdbdd3781b7058bcc339ab43da8 applied, and the platform I/F is preferred. > Disabling the ACPI > control when we have no idea whether there's a platform driver available > for the machine doesn't seem like the right fix. > But once we enable the ACPI backlight control, the platform backlight control is not available any more. In these bugs, the _BCL/_BCM/_BQC method is really not well implemented. in bug 12249 and 12037, 1. the first two elements in _BCL are NOT the backlight levels when the platform is on AC or battery. 2. _BQC returns the index of the current brightness in _BCL package rather than the value, which surely breaks the ACPI video driver. in bug 12302 1. the first two elements in _BCL are NOT the backlight levels when the platform is on AC or battery. 2. every elements in the _BCL package is not a percentage of the maximum brightness, which is also a violation of ACPI spec. yes, we can make the ACPI backlight control work by using customized DSDT. But that's not the fix neither. I don't have any better ideas than disable them. thanks, rui -- 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
