[Bug 35577] New: dual/triplehead secondary monitor not detected

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Tue Mar 22 19:06:36 PDT 2011


           Summary: dual/triplehead secondary monitor not detected
           Product: xorg
           Version: git
          Platform: x86-64 (AMD64)
        OS/Version: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Driver/Radeon
        AssignedTo: xorg-driver-ati at lists.x.org
        ReportedBy: mkaar at cc.hut.fi
         QAContact: xorg-team at lists.x.org

Created an attachment (id=44743)
 --> (https://bugs.freedesktop.org/attachment.cgi?id=44743)

Using xf86-video-ati 6.14.1 + xinerama on

In my triplehead configuration one monitor stayed blank. According to log file
no monitors were detected for the second head - instead a default frame buffer
of 1024x768 was created and could be seen on whole desktop screenshots.

Managed to track the problem to drmmode_display.c and code block:

                        if (info->IsPrimary && (num != 0))
                                goto out_free_encoders;
                        else if (info->IsSecondary && (num != 1))
                                goto out_free_encoders;

Radeon HD4870 has three connectors: DVI-0, DIN, DVI-1 numbered 0,1,2

Primary screen is supposed to be connected to DVI-0 and secondary to DVI-1, but
due to the code block above DVI-1 (i.e. num=2) got skipped and the secondary
monitor was not detected.

Adding && (num !=  2) to the else if helped solve my problem for now. Not sure
about what this code is actually supposed to do so I'll just leave the actual
fixing part to someone else.

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