xrandr --auto should turn off disconnected displays to free crtcs

[Ketil Malde]

In most cases, 'xrandr --auto' does the Right Thing configuring the avilable displays. However, after I have used the VGA output of my laptop and return to use the HDMI output from my docking station, I get this message:

    % xrandr --auto
    xrandr: cannot find crtc for output HDMI3

The setup look like this:

    % xrandr
    Screen 0: minimum 320 x 200, current 1366 x 768, maximum 8192 x 8192
    LVDS1 connected 1366x768+0+0 (normal left inverted right x axis y axis) 277mm x 156mm
       1366x768 59.6*+
       1360x768 59.8 60.0
       1024x768 60.0
       800x600 60.3 56.2
       640x480 59.9
    VGA1 disconnected 1024x768+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
    HDMI1 disconnected (normal left inverted right x axis y axis)
    DP1 disconnected (normal left inverted right x axis y axis)
    HDMI2 disconnected (normal left inverted right x axis y axis)
    HDMI3 connected (normal left inverted right x axis y axis)
       1680x1050 59.9 +
       1280x1024 75.0 60.0
       1152x864 75.0
       1024x768 75.1 60.0
       800x600 75.0 60.3
       640x480 75.0 60.0
       720x400 70.1
    DP2 disconnected (normal left inverted right x axis y axis)
    DP3 disconnected (normal left inverted right x axis y axis)

Note that VGA1 is disconnected, but configured with 1024x768. Deconfiguring it works:

    % xrandr --output VGA1 --off
    % xrandr --auto

This isn't entirely obvious to figure out, and I think --auto should do this (i.e. turn off unused displays to free a crtc) automatically. If this is unacceptable for some reason, I suggest the error message should be changed to be more informative, e.g. something like:

    % xrandr --auto
    xrandr: cannot find crtc for output HDMI3. VGA1 is currently configured but disconnected, to free its crtc, use 'xrandr --output VGA1 --off'. To share a crtc, configure HDMI3 with the same mode as a configured display.

(This is on a Lenovo X220, with Oneiric, but I believe many systems have fewer crtcs than display connections)

[Timo Aaltonen (tjaalton)]

makes sense, might be a good idea to post this upstream on bugs.freedesktop.org.