[Bug 93220] [SKL] Can't detect external monitor via HDMI after 2nd hotplug

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=93220

--- Comment #13 from Jim Bride <jim.bride at linux.intel.com> ---
A few things to note from the logs:

Dec 16 04:52:26 u-Precision-5510 kernel: [    1.342758]
[drm:intel_csr_ucode_init] Loading i915/skl_dmc_ver1.bin
Dec 16 04:52:26 u-Precision-5510 kernel: [    1.343350] i915 0000:00:02.0:
Direct firmware load for i915/skl_dmc_ver1.bin failed with error -2
Dec 16 04:52:26 u-Precision-5510 kernel: [    1.343401] [drm:csr_load_work_fn
[i915]] *ERROR* Failed to load DMC firmware, disabling rpm

You'll probably want to look into this and make sure you have the proper DMC
firmware available on the system.

Dec 16 04:52:26 u-Precision-5510 kernel: [   18.470051] nvidia: module license
'NVIDIA' taints kernel.
Dec 16 04:52:26 u-Precision-5510 kernel: [   18.470053] Disabling lock
debugging due to kernel taint
Dec 16 04:52:26 u-Precision-5510 kernel: [   18.475242] nvidia 0000:01:00.0:
enabling device (0006 -> 0007)
Dec 16 04:52:26 u-Precision-5510 kernel: [   18.475410] [drm] Initialized
nvidia-drm 0.0.0 20150116 for 0000:01:00.0 on minor 1

Does this platform have an on-board Nvidia GPU?

Dec 16 04:52:26 u-Precision-5510 kernel: [   20.478421]
[drm:i915_hotplug_work_func] Connector HDMI-A-1 (pin 5) received hotplug event.
Dec 16 04:52:26 u-Precision-5510 kernel: [   20.478422] [drm:intel_hdmi_detect]
[CONNECTOR:44:HDMI-A-1]

We're definitely at least seeing some hot plug activity on the proper HDMI
port.

Dec 16 04:52:35 u-Precision-5510 kernel: [   28.865318]
[drm:intel_disable_pipe] disabling pipe B
Dec 16 04:52:35 u-Precision-5510 kernel: [   28.867350]
[drm:intel_disable_shared_dpll] disable DPLL 1 (active 1, on? 1) for crtc 25
Dec 16 04:52:35 u-Precision-5510 kernel: [   28.867357]
[drm:intel_disable_shared_dpll] disabling DPLL 1

...and yet here we are tearing down the pipe that was associated with our HDMI
connector.  Eventually we seem to be able to detect the HDMI monitor again, but
we have a few other attempts beforehand.  I suspect this (the few failures) is
innocuous, but I'm not super familiar with the HDMI code path so I will look
into it.  

I have a few questions:

* Has this issue been reproduced more than one time?  Is there a deterministic
recipe to reproduce the issue?
* If the issue is reproducible readily, can you reproduce the issue if the
Nvidia module is *not* loaded?  I think it's notable that things seemed to go
south for us shortly after the Nvidia module was loaded.
* If readily reproducible, can it be reproduced with different monitors?

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