Commit 89ab851f authored by imirkin's avatar imirkin Committed by nouveau
Browse files

add note about phantom VGA port on some laptop dGPU's (from yaMatt on IRC)

parent 7561494b
......@@ -166,3 +166,43 @@ Try using a re-parenting compositor. Those compositors usually provide 3D effect
Right now, Nouveau does not support reclocking and other power management feature. This cripples the performance of the GPU a lot along with increasing the power consumption compared to the proprietary driver.
Using Prime with Nouveau may not result in any performance gain right now, but it should in a not-so-distant future.
#### Discrete card will not switch off
Some secondary GPUs report that they have the VGA port enabled. This has been seen on the GeForce GT 520M.
Symptoms include higher drain on the battery, fans constantly running, Xorg attempting to treat the discrete card as a secondary monitor.
This issue can be detected by opening a console and typing `xrandr`:
[root@localhost ~]# xrandr
Screen 0: minimum 8 x 8, current 2390 x 768, maximum 32767 x 32767
LVDS1 connected primary 1366x768+0+0 (normal left inverted right x axis y axis) 293mm x 164mm
1366x768 60.02*+
1024x768 60.00
800x600 60.32 56.25
640x480 59.94
DP1 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
VGA1 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)
VGA-1-2 connected 1024x768+1366+0 (normal left inverted right x axis y axis) 0mm x 0mm
1024x768 60.00*
800x600 60.32 56.25
848x480 60.00
640x480 59.94
1024x768 (0x63) 65.000MHz
h: width 1024 start 1048 end 1184 total 1344 skew 0 clock 48.36KHz
v: height 768 start 771 end 777 total 806 clock 60.00Hz
800x600 (0x64) 40.000MHz
h: width 800 start 840 end 968 total 1056 skew 0 clock 37.88KHz
v: height 600 start 601 end 605 total 628 clock 60.32Hz
800x600 (0x65) 36.000MHz
h: width 800 start 824 end 896 total 1024 skew 0 clock 35.16KHz
v: height 600 start 601 end 603 total 625 clock 56.25Hz
In this instance you can see there is an LVDS1 connector which is the panel connected to the iGPU. We also have a VGA1 which is the VGA port on the laptop, and VGA-1-2. This is the VGA port that the discrete GPU claims it has, but in reality doesn't.
To get your machine working to its optimum we need to disable that VGA-1-2 port. This has to be accomplished by adding `video=VGA-2:d` to the kernel command line. (Note the -2 corresponds to the last -2 in the connector name reported by xrandr.)
Be aware that in some instances this could mean your external VGA port may no-longer work. This is because it is possible that the discrete GPU really is connected directly to the VGA port on your laptop.
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