screen of one monitor goes black when X Windows starts on dual monitor configuration on a single radeon card

[Bill_H]

Two HP 2311x 1920x1080 monitors on the two HDMI ports, that xrandr reports as DisplayPort-1 and HDMI-0, of a VisionTek Radeon HD 7750 3M 4K 2GB graphics card. FreeBSD 11.1-RELEASE-p9 with MATE 1.18.0.

Computer boots with both monitors mirroring the console. After startx is run to start MATE, one monitor goes black and the other monitor shows half the desktop. Windows that open in the black side of the desktop show in the workspace switcher and can be moved to the visible half of the desktop.

How do I make the other half of my desktop visible?

The graphics cards has a mini-DisplayPort that isn't used. The computer has an integrated graphics chip that isn't used.

pciconf shows:
vgapci0@pci0:4:0:0:    class=0x030000 card=0x77501545 chip=0x683f1002 rev=0x00 hdr=0x00
    vendor     = 'Advanced Micro Devices, Inc. [AMD/ATI]'
    device     = 'Cape Verde PRO [Radeon HD 7750/8740 / R7 250E]'
    class      = display
    subclass   = VGA
vgapci1@pci0:7:0:0:    class=0x030000 card=0x086d15d9 chip=0x20001a03 rev=0x30 hdr=0x00
    vendor     = 'ASPEED Technology, Inc.'
    device     = 'ASPEED Graphics Family'
    class      = display
    subclass   = VGA

xorg.conf was generated with Xorg -configure and modified:
To the Monitor0 section, I added:
> Option "Monitor-DisplayPort-1" "Monitor0"
To the Monitor1 section, I added:
> Option "Monitor-HDMI-0" "Monitor1"
To the Screen1 section, I changed:
< Device "Card1"
to
> Device "Card0"

Both ports have been used individually for a single head configuration without any problem. I have swapped HDMI cables on the ports and seen the visible half of the desktop switch monitors. I have used twm instead of MATE and seen the same issue.

I have tried to use the 'Monitor Preferences' gui to turn off the black screen hoping that turning it back on would do the trick. But turning it off grays and locks the visible screen and leaves the black half unchanged. At that point I'm unable to see a virtual terminal, but by typing the keystrokes blindly, I'm able to reboot the computer.

Thanks for any help,

Bill

Update:
The card has a mini DisplayPort on top and two HDMI ports below. The mini DisplayPort is seen as DisplayPort-0 and no monitor is cabled to it. The upper HDMI port is reported as HDMI-A-1/HDMI-0 (dmr/xrandr). This is the problem port. The lower HDMI port is reported as DP-2/DisplayPort-1. I've attached the relevant section of dmesg showing the drm messages.

Because I had run a single head configuration on either HDMI port, I didn't think it mattered whether the driver thought it was an HDMI port or a DisplayPort port.

BTW, the activity light on the monitor that is black show that the monitor is active, not sleeping.

 

[roddierod]

Your xrandr.txt reports Display-0 as not being connected. You probably need to tell xrandr how to active it.

try something like n an terminal window and see if it activates it:

xrandr --output Display-0 --auto --output HDMI-0 --auto --right-of Display-0

When I ran multi-screens with a Radeon I had to put something similar in my .xinitrc to get them to work correctly.

 

[Bill_H]

DisplayPort-0 was shown as not connected because it was a mini-DisplayPort and I didn't have an adapter or cable for it. The two monitors were plugged into DisplayPort-1 and HDMI-0.

I ran the suggested xrandr command for DisplayPort-1 and HDMI-0 with no change in the results.

I simplified my xorg.conf to include just the Device Section for the radeon driver.

I purchased a mini-DisplayPort to HDMI adapter and tried the setup with three monitors. DisplayPort-0 shows its part of the desktop, DisplayPort-1 is black (but active), and HDMI-0 has a pattern of colored vertical lines.

I have tried:
1) one monitor on one graphics card port; works as expected. Tried for all three ports and all three monitors.
2) with three monitors connected and playing with the "Displays" applet, by reducing the resolution of all three monitors, the HDMI-0 monitor showed its section of the desktop. This only happened a couple of times and I haven't been able to reliably reproduce this.
3) currently, with three monitors connected, trying to configure xorg.conf ServerLayout so that only one screen/monitor is used in the display. Xorg.0.log shows that the one monitor layout is read, but there is no difference in the display: same problem as when I first connected three monitors.