[Bug 89420] New: DELL U2415 monitor detection issue

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89420

            Bug ID: 89420
           Summary: DELL U2415 monitor detection issue
           Product: xorg
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Driver/Radeon
          Assignee: xorg-driver-ati at lists.x.org
          Reporter: bugs.freedesktop at nexigon.net
        QA Contact: xorg-team at lists.x.org

As advised on launchpad.net I'm reporting this issue upstream:
https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/1412730

HW: HP Elitebook 8749w
video: Mobility Radeon HD 5870
OS:   Ubuntu 14.04.2
xorg: 1:7.7+1ubuntu8

My Laptop HP Elitebook 8740w has two external screens connected, 1 DELL U2412M
connected to vga connector, and 1 DELL U2415 connected to Displayport.

When booting up and with screens attached and active, the 2415 boots in
1024x768 resolution, the 2412 boots at the same moment in 1920x1200 as it
should. At the point where the login screen appears the 2415 goes in power save
mode, most of the time. After logging in, turning the 2415 off and on,
sometimes helps the get the screen active (out of power save). Also switching
VT7 to another and back helps.
When it gets active, the resolution is 1024x768, not 1920x1200.
In unity-control-center in display settings the 2415 is displayed as "Unknown
Display" and the maximum resolution I can select is 1024x768.

Tried windows 8.1, no issues with both screens.
Tried fglrx, not theses issues, but lag.

Current partial workaround:
Exported edid form U2415 and booting now with kernel commandline parameter
drm_kms_helper.edid_firmware=DP-1:edid/U2415.edid
With this workaround, only power save issue exists.

Please advise if you need more info

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