Can't use third monitor, Radeon HD 8830M
Alex Deucher
alexdeucher at gmail.com
Tue Sep 11 17:48:58 UTC 2018
On Tue, Sep 11, 2018 at 12:24 PM Eino Virtanen <eino.vir at gmail.com> wrote:
>
> Hello everyone,
>
> I have three monitors. Each connected with DVI cables to a Radeon HD
> 8830M. Two of them are connected with a DVI-DP adapter. The problem is
> that I can only enable two of the monitors simultaneously, otherwise I
> get this error message: "xrandr: Configure crtc 0 failed"
Are you using active or passive DVI->DP adapters? Are all of the
displays on a single GPU? Your GPU only has two PLLs for non-DP
displays, so it can only drive two independent sets if display timing.
If you want to use more than 2 non-DP monitors, you need to use the
exact same modeline on at least two of them. All of the modes you are
trying to set have different timings, so it's not possible:
1680x1050 (0x81) 146.250MHz -HSync +VSync +preferred
h: width 1680 start 1784 end 1960 total 2240 skew 0 clock 65.29KHz
v: height 1050 start 1053 end 1059 total 1089 clock 59.95Hz
1920x1200 (0x8c) 154.000MHz +HSync -VSync *current +preferred
h: width 1920 start 1968 end 2000 total 2080 skew 0 clock 74.04KHz
v: height 1200 start 1203 end 1209 total 1235 clock 59.95Hz
1680x1050 (0x8f) 119.000MHz +HSync -VSync *current +preferred
h: width 1680 start 1728 end 1760 total 1840 skew 0 clock 64.67KHz
v: height 1050 start 1053 end 1059 total 1080 clock 59.88Hz
Try either selecting a modeline that is common across at least two of
the displays, or use randr to add one of the 1680x1050 modelines to
the other connector and hope that the monitor will support it.
Alex
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