Bug 35894 - Displaying across 3 monitors with max resolution causes one monitor to enter power-saving mode (HD6870)
Summary: Displaying across 3 monitors with max resolution causes one monitor to enter ...
Status: RESOLVED MOVED
Alias: None
Product: DRI
Classification: Unclassified
Component: DRM/Radeon (show other bugs)
Version: unspecified
Hardware: x86-64 (AMD64) Linux (All)
: medium normal
Assignee: Default DRI bug account
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Reported: 2011-04-01 20:12 UTC by woogie
Modified: 2019-11-19 08:18 UTC (History)
3 users (show)

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Description woogie 2011-04-01 20:12:00 UTC 
Using arandr, or KDE's RandR manager, I'm trying to adjust my display to stretch across 3 monitors. One of the monitors enters power-saving mode when I try this. Monitors are, from left to right:

DVI-1 (1680x1050 LCD)
DisplayPort-1 (1920x1080 LCD)
DVI-0 (1680x1050 LCD)

Configuring a desktop with all monitors set to their maximum resolution causes one of the two DVI-connected monitors to enter power-saving mode. The mouse cursor will still "disappear" into this monitor as if it were enabled. No error messages appear in either X.org.log or dmesg. It is non-deterministic as to which monitor turns off of the two DVI-connected monitors.

I can configure a desktop with, for example, 1280x1024, 1920x1080, 1280x1024 for resolutions (left to right) and all three monitors will function properly. I cannot use 1680x1050, 1280x1024, 1680x1050, as one of the DVI monitors will enter power saving mode. 

I have tested, and this hardware configuration will function with the proprietary fglrx driver, and under Windows, so the card/monitors do not appear at fault.

I have tried the 2.6.38 release candidate kernels, and this feature has never functioned correctly, so I don't think it's a regression.

HARDWARE:
PowerColor HD6870
AMD 1075T
12Gb RAM
Asus M4A89/GTD-PRO USB3
DVI-1: LG Flatron W2242TQ
DisplayPort-1: Dell UV22H
DVI-0: ASUS (unknown)

OS:
ArchLinux, 64-bit with:
Kernel26, 2.6.38.2-1
xf86-video-ati 6.14.1-1
xorg-server 1.10.0.901-1
libdrm 2.4.24-1
ati-dri 7.10.1-1

Please let me know if I can provide any additional details. I am willing to apply patches to the kernel or other packages as needed to test.
Comment 1 woogie 2011-04-03 09:04:24 UTC 
I've experimented further with RandR, and I've found some additional information:

A configuration of 1680x1050,inactive,1680x1050 does function correctly.

At boot, with KMS enabled, two of my three displays are active when the radeon module loads: DisplayPort-1 and one of the two DVI displays.

If I use ctrl+alt+f1 to switch back to a console when I have my display configured to use DVI-1 and DVI-0, one of the DVI displays will enter power saving mode and DisplayPort-1 will turn back on. If I then use ctrl+alt+f7 to re-enter my desktop, DisplayPort-1 turns off leaving only one of the two DVI displays enabled.

I'm also having trouble coming up with consistent use cases, as behaviour is not consistent. For example, I have tried configuring 1280x1024,1280x1024,1280x1024 for my displays, and have received inconsistent results; sometimes all displays function, other times I have had one of the three displays (including DisplayPort-1) enter power-saving mode.

UPDATE:

DisplayPort-1 is actually a U2211H, not UV22H
Comment 2 woogie 2011-04-24 08:11:47 UTC 
Results are still repeatable, using updated software stack as follows:

ati-dri 7.10.99.git20110412
xf86-video-ati 6.14.1
xorg-server 1.10.1
kernel 2.6.39-rc3
Comment 3 Martin Peres 2019-11-19 08:18:50 UTC 
-- GitLab Migration Automatic Message --

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