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Monitor blank after using KVM switch. Radeon/displayport
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Yazka
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Joined: 07 Mar 2007
Posts: 8
Location: Tampere, Finland

PostPosted: Mon Mar 30, 2015 8:22 am    Post subject: Monitor blank after using KVM switch. Radeon/displayport Reply with quote

Hey,

Nooblar in trouble :)

Setup: Monitor 1 plugged in only to Radeon 6970's DVI-0. Monitor 2 plugged in to same 6970's DisplayPort-0 via KVM switch. Second input to that switch connects to Radeon 290x which is using pci-stub so it shouldn't be a factor(?). Using opensource Radeon driver. Kernel 3.19.0-gentoo, xorg-drivers 1.16.

Issue:Monitor returns blank after cycling it's power or using KVM switch. Xrandr reports it still plugged.
Code:
xrandr --output DisplayPort-0 --off &&  xrandr --output DisplayPort-0 --auto --right-of DVI-0
returns the display without fail. dmesg doesn't report errors.

So it's a power management issue, right? I don't know where to start troubleshooting because I'm not getting error messages. Any input is appreciated.

EDIT Forgot important detail: Only the display connected to displayport has this behavior (and even it didn't when it was connected via DVI). The other one, one on DVI port, return the picture after power cycle as it should.
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chithanh
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Joined: 05 Aug 2006
Posts: 2152
Location: Berlin, Germany

PostPosted: Tue Mar 31, 2015 8:35 am    Post subject: Reply with quote

It is probably a bug in the radeon driver. DisplayPort requires link training every time you connect a monitor. It appears that the disconnect is not recognized, or the KVM switch does things that confuse the driver.

In any case, reporting this issue to https://bugs.freedesktop.org/ would be a good idea.
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Yazka
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Joined: 07 Mar 2007
Posts: 8
Location: Tampere, Finland

PostPosted: Tue Mar 31, 2015 10:32 am    Post subject: Reply with quote

chithanh wrote:
It is probably a bug in the radeon driver. DisplayPort requires link training every time you connect a monitor. It appears that the disconnect is not recognized, or the KVM switch does things that confuse the driver.

In any case, reporting this issue to https://bugs.freedesktop.org/ would be a good idea.


Thank you for the reply. I wasn't aware of the link training. I'll check if the issue is still there if I connect the display directly to the GPU via DisplayPort. I'll file a bugreport when I know if the issue exists without the KVM switch.
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