Created attachment 120039 [details]
As reported at Launchpad:
and to mailinglist:
After resuming from suspend-to-ram, graphics on displayport connected Dell U2415 monitor are sluggish and input has lag.
- transition from unity greeter login locked status to unlocked status: 6 seconds (normal 1 second)
- transition from clicking dash and getting window: 2-3 seconds (normal <1 second)
- starting gedit: 4 seconds (normal <1 second)
- mouse lags, sometimes the pointer is still on the left side of the screen, while it should be on the right
- input from keyboard lags, about 1-2 seconds (normal no lag)
When unplugging the Displayport cable all lag is gone.
When plugging displayport back in again lag is back, same as before.
After a reboot, response of graphics and input is normal. So two options to get rid of the lag: unplug DP or reboot.
Did a mainline kernel bisect:
From 3.13.11-ckt27 (good) to v4.3-wily (bad)
First bad is v4.0-rc1-vivid
Did a kernel commit bisect:
From 3.19 (good) to 4.0-rc1 (bad)
first bad commit: [e55bca26188e45f209597abf986c87cc5a49894a] radeon/audio: enable DP audio
Commit bisect log is attached
However, I'm not able to use audio over Displayport.
Created attachment 120040 [details]
Created attachment 120041 [details]
Created attachment 120042 [details]
Created attachment 120439 [details]
dmesg with drm.debug=14
Maybe this gives an extra clue.
Dmesg with drm.debug=14 from boot to logged-in and following suspend resume. Done with kernel v4.3
Also tested with v4.4-rc4, but since 4.4-rc1 my laptop won't suspend properly.
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