Testing and Troubleshooting: Linux Source Device
$ sudo apt-get install read-edid
...
$ sudo get-edid | parse-edid On Linux you can use xrandr to see if the display is correctly detected.
In the below example the LVDS1 is the internal screen.
The HDMI2USB is connected to DisplayPort port on a X220 Laptop via a [DisplayPort to HDMI adapter]. As this device has a DP++ port, this configuration appears as HDMI1 rather than DP1. (In this configuration the [DisplayPort to HDMI adapter] is a passive device and the conversion is happening in your computer!)
# xrandr
LVDS1 connected primary 1366x768+0+0 (normal left inverted right x axis y axis) 277mm x 156mm
1366x768 60.0*+
1360x768 59.8 60.0
1024x768 60.0
800x600 60.3 56.2
640x480 59.9
VGA1 disconnected (normal left inverted right x axis y axis)
HDMI1 connected 1024x768+1366+0 (normal left inverted right x axis y axis) 0mm x 0mm
1024x768 60.0*+
DP1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
HDMI3 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
DP3 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)
# The Raspberry Pi is a little complicated as the display isn't renegotiated properly.
You need to boot the Pi while connected to the HDMI2USB so it detects the correct resolution.
You can force the Raspberry Pi into the right resolution otherwise with XXXXX boot options. FIXME: Add more information here.
pi@raspberrypi ~ $ DISPLAY=:0.0 xrandr
xrandr: Failed to get size of gamma for output default
Screen 0: minimum 1024 x 768, current 1024 x 768, maximum 1024 x 768
default connected 1024x768+0+0 0mm x 0mm
1024x768 0.0*
pi@raspberrypi ~ $
