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While testing display port (both the mini dp connector as well as dp over usb-c) on a Lenovo P50 I'm seeing DP training errors, these seem to happen when changing the mode on the monitor. Initially plugging in the monitor works, then after a suspend resume I hit bug 1390274, and the switch to the mirror mode causes displaylink training errors, this might be related to the mode not being supported by the monitor ? The training errors seem to cause monitor unplug + plug events, at which point the EDID race described in bug 1390274 hits and g-s-d goes into a loop. Sometimes during the loop it seems to get the right EDID and briefly the DP external monitor comes up in its native resolution, but the loop continues (I think g-s-d get behind processing events?). If g-s-d manages to gets to a stable situation it is the mirror mode at a resolution not actually supported by the monitor (as described in bug 1390274). This happens sometimes (usually after a suspend resume) if I then try to manually fixup the config, it quickly goes into the loop again and typically it will not exit the reconfigure loop unless I unplug the monitor. I think that nouveau needs to be changed to retry training a couple of times before reporting an unplug to userspace.
*** Bug 1390274 has been marked as a duplicate of this bug. ***
Ok, so the real issue here is that we are getting spurious KEY_SWITCHVIDEOMODE keypress events on hotplug and on modeset, causing the g-s-d loop. So I started with a patch adding an ACPI notifier callback intercepting ACPI_VIDEO_NOTIFY_PROBE events stopping the KEY_SWITCHVIDEOMODE keypress events, breaking the loop, but that breaks hotplug detect when the Nvidia GPU is runtime suspended. There are 2 issues here: 1) Some bugs fixed in drm-next which are needed for hotplug to work on Maxwell GPUs in general 2) The GPU not seeing hotplug events when runtime suspended even with bugs from 1) fixed. To fix 2. I added code to wake the GPU from runtime suspend on ACPI_VIDEO_NOTIFY_PROBE events, this does correctly wake the GPU up, but it does not see the hotplug events (likely because the interrupts triggered while it was suspended). So next revision I added code to explicitly re-check the status of all connectors on ACPI_VIDEO_NOTIFY_PROBE events, which fixes the hotplug issues for real while also stopping the spurious KEY_SWITCHVIDEOMODE keypress events which were causing both the g-s-d loop as well as bug 1390274. I'm attaching 3 patches for future reference here, 2 bug-fixes already in drm-next and the final version of the ACPI_VIDEO_NOTIFY_PROBE handling patch.
Created attachment 1219700 [details] 0001-i2c-aux-g94-retry-transactions-after-hw-reports-an-e.patch
Created attachment 1219701 [details] 0002-i2c-gk110b-gm10x-use-the-correct-implementation.patch
Created attachment 1219702 [details] 0003-drm-nouveau-Intercept-ACPI_VIDEO_NOTIFY_PROBE.patch
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