Rick Stevens writes:
On Thu, 2007-12-13 at 19:41 -0500, Sam Varshavchik wrote:Frank Cox writes: > On Wed, 12 Dec 2007 19:57:55 -0500 > Sam Varshavchik <mrsam@xxxxxxxxxxxxxxx> wrote:> >> My laptop seemingly has an ambient light sensor, of some kind, and the >> kernel apparently knows about it, but won't let me access it. > > Are you sure it's kernel-controlled? Perhaps it's 100% hardware. > > Try covering that sensor when you're looking at Grub and see if it brightens> or dims the screen then.Tried that. No response in Grub, the LCD backlight begins reacting to the ambient light sensor as soon as the kernel boots, even before initscripts mount all the filesystems.Can you disable it in the BIOS?
There are no BIOS settings, and it only begins working after the Linux kernel gets loaded. As I said: the sensor is not active when Grub's menu is shown, only after the kernel is loaded.
This is but a minor irritation, but I want to track it down just for the sheer mystery factor: here I have this hardware device that all evidence suggests is directly supported by the kernel. It does not get activated until the kernel boots, so it cannot be purely a BIOS-controlled function. It is not control by X.org, or Gnome, because I can get the light sensor to react even before initscripts mount their partition. Direct support in the kernel is the only choice left.
Yet, I find no apparent kernel module, and I find nothing in /proc or /sys that gives any hint of this sensor's existence. The only thing I can think of is that this is an ACPI function, but my knowledge of ACPI is rather scant.
This is an irritant because my normal light levels in the room happen to just hit that sweet spot where the ambient light sensor starts dimming the LCD backlight just slightly. The dim function is not absolute, it is gradual. The sensor can dim the backlight in small steps, between full and less-than-half regular brightness level.
So, with the ambient room light level right at the top of the sensor's threshold, for the longest time I thought that my eyes were playing tricks on me, because I could've sworn that the brightness of the laptop's display kept flickering back and forth.
Only some time later did I discover of the sensor's existence (because nothing in Gnome, or /var/log/message gave any hint of its presence), and figured out that the stupid thing was frobbing the LCD backlight's power a few notches back and forth, with the ambient light level right at the top of the sensor's threshold. It was driving me nuts, until I figured this out. Now, I just want to turn the blasted thing off, and leave the LCD backlight at full power, all the time.
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