On 04/01/2013 09:03 PM, Seth Forshee wrote: > On Mon, Apr 01, 2013 at 09:53:36AM +0800, Aaron Lu wrote: >> On 02/12/2013 12:21 AM, Seth Forshee wrote: >>> The AML implementation for brightness control on several ThinkPads >>> contains a workaround to meet a Windows 8 requirement of 101 brightness >>> levels [1]. The implementation is flawed, as only 16 of the brighness >>> values reported by _BCL affect a change in brightness. _BCM silently >>> discards the rest of the values. Disabling Windows 8 compatibility on >>> these machines reverts them to the old behavior, making _BCL only report >>> the 16 brightness levels which actually work. Add a quirk to do this >>> along with a dmi callback to disable Win8 compatibility. >> >> If we disable the _BQC(i.e. set cap._BQC=0) for these systems, will the >> problem go away? If so, I think perhaps we can put these systems into a >> _BQC quirk table and set cap._BQC=0 for them. > > That helps a little, but we're still left with only 16 of the 101 > brightness levels causing any change in brightness. The firmware isn't > rounding the "bad" values or anything like that; it just silently > ignores them. OK, and if GUI tool like g-s-d decides to go some more steps when adjusting backlight level, it may always choose the non-functional values. Hmm, doesn't seem to be an usable way then. I really wondered, how Windows handled this, it should have the same problem, unless they are not using the acpi video interface? > > I submitted a second set of patches [1] which writes all intermediate > values between the old and new brightness values and disables _BQC for > these machines (empirically rather than using a quirk table), though no > one seems to be interested in reviewing them. Suppose we are at level 100, and the user sets the target level to be 20, then we will need to call _BCM 80 times? Thanks, Aaron -- 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
