Re: "Windows 2012" OSI causes backlight problems on current ThinkPad firmware

[joeyli <jlee@suse.com>]

於 一，2012-12-24 於 16:32 -0500，Ben Jencks 提到：
> The addition of "Windows 2012" to the OSI strings in the 3.7 cycle has
> caused backlight brightness adjustment to break on my ThinkPad T530.
> 
> Without "Windows 2012" _BCL returns the actual 16 brightness levels:
> 
> 5, 10, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 90, 100
> 
> When "Windows 2012" is present, it returns 101 levels 0-100, but _BCM
> rounds any value up to one of the real values above.
> 
> This interacts badly with gnome-settings-daemon, which attempts to
> change brightness in increments of 5 (1/20 of 100). If brightness is
> currently 100, it attempts to decrement it to 95, but it gets rounded
> back up to 100, so it's impossible to decrease the brightness.
> 
> Booting with acpi_osi="!Windows 2012" fixes the problem, though I'm
> not
> sure if it introduces others; I see several other things depend on
> WIN8
> in DSDT.
> 
> Perhaps this should be fixed in gnome-settings-daemon, but since it
> appears on the surface to be a kernel regression (3.6 works, 3.7
> broken)
> I thought I'd report it here first. 

Yes, this is g-s-d's problem, g-s-d should adapt to more levels of
brightness:

plugins/power/gsd-power-manager.c

/* on ACPI machines we have 4-16 levels, on others it's ~150 */
#define BRIGHTNESS_STEP_AMOUNT(max) ((max) < 20 ? 1 : (max) / 20)



Thanks a lot!
Joey Lee

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