KMS does not allow the user to pre-select a resolution

Bug #530216 reported by Andy Whitcroft on 2010-03-01
This bug affects 2 people
Affects Status Importance Assigned to Milestone
linux (Ubuntu)
Andy Whitcroft

Bug Description

There are times when KMS has incomplete or incorrect resolution data. This includes when it has no EDID data or faked EDID data as often occurs with KVM switches. In these circumstances there is apparently no way to override the resolution selection in the kernel to correct any issues.

It seems likely we would need a kernel command line option or module parameter or similar to fix this early enough.

Andy Whitcroft (apw) on 2010-03-01
Changed in ubuntu:
milestone: none → ubuntu-10.04-beta-1
affects: ubuntu → linux (Ubuntu)
Andy Whitcroft (apw) on 2010-03-08
Changed in linux (Ubuntu):
milestone: ubuntu-10.04-beta-1 → ubuntu-10.04-beta-2
tags: added: kernel-series-unknown
Steve Conklin (sconklin) on 2010-03-25
Changed in linux (Ubuntu):
assignee: nobody → Steve Conklin (sconklin)
Steve Conklin (sconklin) on 2010-03-25
Changed in linux (Ubuntu):
importance: Undecided → High
Andy Whitcroft (apw) wrote :

Seems there is a mechanism. The frambuffer mode selection interface applies to the DRM connectors. This means that you can sepecify a mode per output as below on the kernel command line:


Where output its the name of the output as per xrandr, say VGA1 or LVDS, and the mode is say 1024x768. The mode may be pretty complex:


Changed in linux (Ubuntu):
assignee: Steve Conklin (sconklin) → Andy Whitcroft (apw)
status: New → Invalid
status: Invalid → Fix Released
status: Fix Released → Invalid
Andy Whitcroft (apw) wrote :

Correction not the names from xrandr, but per the outputs listed in sysfs under /sys/class/drm. in my case I have these files, the connector names are 'VGA-1' etc:

    card0 card0-DisplayPort-2 card0-LVDS-1 controlD64
    card0-DisplayPort-1 card0-HDMI Type A-1 card0-VGA-1 version

Rune K. Svendsen (runeks) wrote :

Hi Andy,
Where did you find the above information?
I'm trying to get it working on my computer, so it'd be nice if there was a place that explained it a bit more in detail.

Rune K. Svendsen (runeks) wrote :

I'll just add what I've learned for now.
The kernel video-parameter seems to work for me if I leave out the output from the line (this is also the experience of at least one other guy I read about on the #radeonhd IRC channel).
So adding the following line to grub's default kernel parameters (GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub), makes my virtual terminals display at the specified resolution:
(the refresh rate ("@85") was optional for me).
Neither the output names listed by xrandr or in /sys/class/drm worked.

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