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Old 12-12-2007, 11:57 PM
Sam Varshavchik
 
Default Ambient light sensor configuration?

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. With the room
lights reduced, the LCD's backlight gradually steps down to half power, and
goes back to full power when the lights come back up. I can force this to
happen by manually covering up the sensor.


Nothing ACPI-related appears to be logged, when I play with the sensor. I
find nothing interesting in /proc. Nothing interesting in the laptop's BIOS
setup either.


I don't care for the light sensor. I want the LCD backlight to always run at
full power. To hell with global warming, I want to burn as much juice as I
can, but I can't find a way to disable it. Nothing in Gnome Power Management
has any effect, and this ambient light sensor seems to operate completely
independent on any power setting. So, how do I disable this thing? By
disable I don't mean to cover it up with black tape, and keep the LCD
backlight at half power, all the time. Quite the opposite.



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Old 12-13-2007, 12:55 AM
Frank Cox
 
Default Ambient light sensor configuration?

On Wed, 12 Dec 2007 19:57:55 -0500
Sam Varshavchik <mrsam@courier-mta.com> 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.

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Old 12-13-2007, 01:25 AM
Tony Nelson
 
Default Ambient light sensor configuration?

At 7:57 PM -0500 12/12/07, Sam Varshavchik 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. With the room
>lights reduced, the LCD's backlight gradually steps down to half power, and
>goes back to full power when the lights come back up. I can force this to
>happen by manually covering up the sensor.
>
>Nothing ACPI-related appears to be logged, when I play with the sensor. I
>find nothing interesting in /proc. Nothing interesting in the laptop's BIOS
>setup either.
>
>I don't care for the light sensor. I want the LCD backlight to always run at
>full power. To hell with global warming, I want to burn as much juice as I
>can, but I can't find a way to disable it. Nothing in Gnome Power Management
>has any effect, and this ambient light sensor seems to operate completely
>independent on any power setting. So, how do I disable this thing? By
>disable I don't mean to cover it up with black tape, and keep the LCD
>backlight at half power, all the time. Quite the opposite.

Mirror? Reflect light from the display back to the sensor in a positive
feedback loop.

Small LED? Shine it on the sensor.

Disable power management? Might have no effect.

Disable ACPI? Might have no effect.

LKML? They should know where the code is.
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Old 12-13-2007, 07:22 AM
Tomasz Torcz
 
Default Ambient light sensor configuration?

Dnia 12-12-2007, śro o godzinie 19:57 -0500, Sam Varshavchik pisze:
> I don't care for the light sensor. I want the LCD backlight to always run at
> full power. To hell with global warming, I want to burn as much juice as I
> can, but I can't find a way to disable it. Nothing in Gnome Power Management
> has any effect, and this ambient light sensor seems to operate completely
> independent on any power setting. So, how do I disable this thing? By
> disable I don't mean to cover it up with black tape, and keep the LCD
> backlight at half power, all the time. Quite the opposite.

/apps/gnome-panel-manager/ambient

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Old 12-13-2007, 11:12 AM
Sam Varshavchik
 
Default Ambient light sensor configuration?

Tomasz Torcz writes:



Dnia 12-12-2007, śro o godzinie 19:57 -0500, Sam Varshavchik pisze:
I don't care for the light sensor. I want the LCD backlight to always run at
full power. To hell with global warming, I want to burn as much juice as I
can, but I can't find a way to disable it. Nothing in Gnome Power Management
has any effect, and this ambient light sensor seems to operate completely
independent on any power setting. So, how do I disable this thing? By
disable I don't mean to cover it up with black tape, and keep the LCD
backlight at half power, all the time. Quite the opposite.


/apps/gnome-panel-manager/ambient


The only applet I see is the "Brightness" applet, I don't have any "Ambient"
applet. Is that in a separate package? yum shows nothing obvious.


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Old 12-13-2007, 12:01 PM
Tomasz Torcz
 
Default Ambient light sensor configuration?

Dnia 13-12-2007, czw o godzinie 07:12 -0500, Sam Varshavchik pisze:
> > /apps/gnome-panel-manager/ambient
>
> The only applet I see is the "Brightness" applet, I don't have any "Ambient"
> applet. Is that in a separate package? yum shows nothing obvious.

Sorry, I've mistyped that GConf key. It's under gnome-power-manager.


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Old 12-13-2007, 11:40 PM
Sam Varshavchik
 
Default Ambient light sensor configuration?

Tomasz Torcz writes:



Dnia 13-12-2007, czw o godzinie 07:12 -0500, Sam Varshavchik pisze:

> /apps/gnome-panel-manager/ambient

The only applet I see is the "Brightness" applet, I don't have any "Ambient"
applet. Is that in a separate package? yum shows nothing obvious.


Sorry, I've mistyped that GConf key. It's under gnome-power-manager.


I didn't even realize you were referring to a gconf key -- I was looking for
an applet.


Anyway, I see this setting now, but disabling it made no difference, even
after I reboot. Even if I reboot to run level 1, the LCD backlight reacts to
the ambient light sensor. Further experimentation showed that:


1) No dimming when I'm on the GRUB boot menu. The ambient light sensor has
no effect.


2) The ambient light sensor begins effecting the LCD backlight as soon as
the kernel boots, even before initscripts have all the filesystems mounted.


So, there may be some Gnome support for ambient light sensors, but in my
case I see no other explanation but this is something that's directly
handled in the kernel. I see nothing that immediately stands out in 'lsmod'.


Grepping through the various kernel modules, the only culprit I can find is
a "tsl2550.ko' -- a "TSL2550 ambient light sensor driver", but I don't have
this module loaded at all


Strange mystery.

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Old 12-13-2007, 11:41 PM
Sam Varshavchik
 
Default Ambient light sensor configuration?

Frank Cox writes:


On Wed, 12 Dec 2007 19:57:55 -0500
Sam Varshavchik <mrsam@courier-mta.com> 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.


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Old 12-14-2007, 12:33 AM
Rick Stevens
 
Default Ambient light sensor configuration?

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@courier-mta.com> 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?

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- LOOK OUT!!! BEHIND YOU!!! -
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Old 12-14-2007, 01:52 AM
Sam Varshavchik
 
Default Ambient light sensor configuration?

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@courier-mta.com> 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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