Bug 3483 - xset dpms force off does not turn off LCD backlight
Summary: xset dpms force off does not turn off LCD backlight
Alias: None
Product: xorg
Classification: Unclassified
Component: Driver/Radeon (show other bugs)
Version: 6.8.2
Hardware: x86 (IA32) Linux (All)
: high normal
Assignee: Xorg Project Team
QA Contact: Xorg Project Team
Depends on:
Reported: 2005-06-06 18:23 UTC by Xiaotian Sun
Modified: 2007-08-31 07:11 UTC (History)
3 users (show)

See Also:
i915 platform:
i915 features:

My Radeon X600 xorg.conf file. (2.68 KB, text/plain)
2006-06-22 15:07 UTC, James Ralston
no flags Details
My Radeon X600 xorg.conf file. (2.68 KB, text/plain)
2006-06-22 15:10 UTC, James Ralston
no flags Details
My Radeon X600 Xorg.0.log file. (136.09 KB, text/plain)
2006-06-22 15:12 UTC, James Ralston
no flags Details

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Description Xiaotian Sun 2005-06-06 18:23:53 UTC
"xset dpms force off" blank the screen, but the LCD backlight is still on, and
the monitor is not in standby mode (green light on my Dell 2001FP, instead of

Tested with Radeon 9100 IGP, DVI-D connection, Dell 2001FP LCD.
Comment 1 T. Hood 2005-09-29 04:30:24 UTC
Possibly related to #1666.
Comment 2 Peter Galiovsky 2005-11-19 21:44:31 UTC
Similar behaviour here. On a ThinkPad T30, "xset dpms force off" just blanks the
screen, but doesn't turn off the backlight. This is particulary annoying when
trying to use suspend-to-RAM as the screen remains still on after suspending.
Even closing the lid doesn't help.

Radeontool (http://fdd.com/software/radeon/) (probably) did the trick. I can't
really tell whether it shuts off the whole monitor or just turns the backlight
off. (Or is it essentially the same?)

Maybe it would be possible to incorporate this functionality into the radeon driver?
Comment 3 James Ralston 2006-06-22 15:05:43 UTC
I have the exact same problem, with a Radeon X600 connected to a Dell 1901FP LCD
monitor via the DVI connector.

From a Linux framebuffer, if I enable DPMS:

$ setterm -powersave powerdown -powerdown 1

...and then wait for DPMS to kick in, the LCD backlight turns off, and the power
light changes from solid green (full on) to solid yellow (off), which is correct

This is under Fedora Core 5, using:

$ rpm -q xorg-x11-server-Xorg

(I also have FC5 running on my laptop (a Dell Latitude D610 with a Radeon
Mobility card) with the same version of Xorg, and I do *not* experience this
problem there.  I've only experienced this problem with the Radeon X600 paired
with the Dell 1901FP LCD monitor.)
Comment 4 James Ralston 2006-06-22 15:07:59 UTC
Created attachment 6023 [details]
My Radeon X600 xorg.conf file.
Comment 5 James Ralston 2006-06-22 15:10:30 UTC
Created attachment 6024 [details]
My Radeon X600 xorg.conf file.
Comment 6 James Ralston 2006-06-22 15:12:03 UTC
Created attachment 6025 [details]
My Radeon X600 Xorg.0.log file.

Please ignore the obsoleted xorg.conf file; that was from the wrong machine.
Comment 7 Michel Dänzer 2006-06-23 00:26:48 UTC
(In reply to comment #3)
> From a Linux framebuffer, if I enable DPMS: [...]

If that's with radeonfb, have you tried Option "UseFBDev" with X?
Comment 8 James Ralston 2006-07-06 09:16:13 UTC
I wasn't using radeonfb; I was just using the plain old Linux console (e.g., tty1).
Comment 9 James Ralston 2006-07-06 09:27:30 UTC
Another data point: just out of curiosity, I temporarily switched from the DVI
cable (digital display input) to the VGA cable (analog display input), and DPMS
worked properly.

So, at least for my Radeon X600 and Dell 1901FP LCD monitor, DPMS fails to
function only when using digital display input.
Comment 10 Xiaotian Sun 2006-07-09 19:31:59 UTC
I second the previous comment.  D-Sub connection doesn't have this problem. 
Tested with Radeon 9100 IGP and Dell 2001FP LCD.
Comment 11 Daniel Stone 2007-02-27 01:26:58 UTC
Sorry about the phenomenal bug spam, guys.  Adding xorg-team@ to the QA contact so bugs don't get lost in future.
Comment 12 Dag Bakke 2007-06-06 02:24:37 UTC
I can confirm this for my Dell Inspiron 8200 with "Radeon R250 [Mobility FireGL 9000]".

I think DPMS suspend -> off drops powerconsumption approximately 1 watt.
Switching off the backlight with radeontool drops the power consumption an additional 4(!) watts. That's a lot for a dinky laptop battery.

This is current released bits + current randr 1.2 branch of the radeon driver.
Comment 13 Dag Bakke 2007-06-06 02:50:30 UTC
I did some closer observations. The drop in power consumption between suspend and off may have been wishful thinking.

Numbers taken from powertop:
fully lit, panel on = 26 watts
blank = 20-21 watts
suspend = 20-21 watts
standby = 20-21 watts
off = 20+ watts (not significantly less than suspend/standby, I think)
radeontool light off = 16 watts

The driver will happily restore light when I press a key, so it looks like the driver plays with the (some of) same registers as radeontool.

I also notice that the Fn-brighter/Fn-darker keycombos doesn't work from within X. They do work in the virtual console, though. Should I open a separate bug for this?
Comment 14 Dag Bakke 2007-06-06 06:51:19 UTC
One more observation. backlight is *not* restored whe hitting a key in the virtual console. Thus I think it is reasonable to conclude that it is the driver which restores the backlight, and not the BIOS.
Comment 15 Alex Deucher 2007-06-12 20:58:09 UTC
fixed for LVDS in master and randr-1.2
Comment 16 Dag Bakke 2007-06-13 00:33:53 UTC
Tested. works for me. James, do you care to test as well, being the original reporter and all...

Otherwise, I'd say the bug is ripe for closing.

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