[Bug 31961] [drm:drm_crtc_helper_set_config] *ERROR* failed to set mode on [CRTC:6]

[bugzilla-daemon-CC+yJ3UmIYqDUpFQwHEjaQ@public.gmane.org]

https://bugs.freedesktop.org/show_bug.cgi?id=31961

--- Comment #12 from Salah Coronya <salah.coronya-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> 2012-06-02 00:45:57 PDT ---
Created attachment 62407
  --> https://bugs.freedesktop.org/attachment.cgi?id=62407
dmesg, kernel 3.4.0 drm.debug=0x06

Here's a better dmesg, however instead of being CTRC 5 and 6; they are 9 and 10
(and so the error is "*ERROR* failed to set mode on [CRTC:10]"). CRTC:9 is the
VGA output, and CRTC:10 is the TV output. However, this card (an NV4E - GeForce
6150 LE - integrated onto the motherboard) HAS no TV output (or a DVI output
either, which is also detected). So CRTC:10 is connected to a phantom output.
Curiously enough, the framebuffer has a physical resolution of CRTC:9 (the
VGA), but a virtual resolution of CRTC:10 (the phantom TV output) - so it only
fills part of the screen.

Adding "video=VGA-1:1280x1024 video=TV-1:d video=DVI-D-1:d" works around the
problem; xorg.conf needs a similar setup to disable the "phantom" output and
specific a sane default resolution for the real one, like this:

Section "Monitor"
    Identifier "TV-1"
    Option "Ignore" "True"
EndSection

Section "Monitor"
    Identifier "DVI-D-1"
    Option "Ignore" "True"
EndSection

Section "Monitor"
    Identifier "VGA-1"
    Option "PreferredMode" "1280x1024"
EndSection

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