[Bug 95141] [BYT] Displayport signals stay on after monitor is unplugged

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=95141

--- Comment #8 from roberth <sarvatt at gmail.com> ---
(In reply to Manasi from comment #7)
> In order to reproduce the bug, I did some PHY testing here on my system with
> drm-intel-nightly (kernel 4.6.0-rc4). I hooked up the HPD and data lines to 
> the oscilloscope to see the signal levels after the DP monitor is
> disconnected. And I saw that signal levels were as low as -1mv after the DP
> monitor is disconnected. Also the HPD signal is 0V DC on the DP disconnect.
> So I am not able to reproduce the issue that you are seeing.
> For me to root cause this bug, I would need the following information from
> you:
> - Could you also hook up the data signals to the oscilloscope and verify if
> there is any signal on those lines after the DP monitor is disconnected.

I do not have an oscilloscope to verify, I'm just using a voltmeter and it was
showing signals on after unplugging DP from what I saw. I can see if the
customer does if that would help though? 

> - From the data you provided, it is strange that the HPD signal is 3.29V on 
> boot. Was this system booted with DP connected? How did you measure this
> electrical signal level? 


I am plugging in a dp cord and measuring it on the pins there with a voltmeter
with one end on the plug case and the other on the pin. Would that make it give
false results? I have been unable to measure directly on the displayport
connector on the machine because it is so small, but I will try again if so.


> - If the DP is not connected on boot and you plug it in later, does the DP
> monitor display it properly and it works?


Yeah that works fine, and there are no excess emissions in that case according
to their testing also.


> - Could you send separate dmesg logs for :
>      Boot without DP connected
>      Then dmesg -c to clear dmesg
>      Plug in DP cable and collect logs
>      dmesg -c
>      Unplug and collect logs


This is what I posted in comments 1-3, but I did it again on 4.4.0 and will
attach those. drm-intel-nightly and drm-intel-next both do not work on this
machine, no displays ever get brought up including the internal one. Would logs
from 4.6.0-rc6 be acceptable? What drm.debug level would be most helpful?


> - Please send the picture of the motherboard to see the connections of the
> HPD pin on the motherboard. Also send us the schematics of the same if you
> have.


Will do ASAP, I will ask for schematics as well to forward them.

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