[Bug 105891] miniDP to external monitor with DVI-D via miniDP to HDMI/DVI-D/DP adapter : DP dual mode HDMI ID: (err -6) and blank screen

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=105891

--- Comment #6 from genpur at o2.pl ---
Created attachment 138626
  --> https://bugs.freedesktop.org/attachment.cgi?id=138626&action=edit
dmesg_Non-problematical_PanasonicTV.log

"Is that the EDID read fails with the troublesome monitor+dongle combination?"

I don't know what is the real cause that problematical monitor is not
activated. This is my main problem. First idea was to connect other device to
dongle instead of problematical monitor, so I connected TV. TV has been
detected without any problem, display was active, everything was working.

Later on, I have found on internet that when people trying to connect some
monitors (esspecially via KVM switch or some video adapters) there can be a
problem with reading EDID from connected display.
So, I ASSUMED that this can be the reason... To avoid situation that my laptop
(because of any reason) can't read EDID properly, I decided to try putting EDID
directly (into kernel parameters on boot stage in grub2 or put into initram
image). I have expected that in this case my integrated Intel grapics card
should force output of miniDP port to desired parameters, like
"video=HDMI-A-1:1280x1024-16 at 75D drm.edid_firmware=HDMI-A-1:edid/monitor.bin".
Result was the same - blank monitor - but parameters
/sys/class/drm/card1-HDMI-A-1/{modes,enabled,status,edid} where correct.

My conclusion was that EDID has been read "locally" from initram image
properly, but it's not enough to activate problematic monitor.

Then I have compared log files of problematical monitor and non-problematical
TV. I saw that only difference is here : [drm:drm_dp_dual_mode_detect
[drm_kms_helper]]

a) when display was activated
DP dual mode HDMI ID: DP-HDMI ADAPTOR\004 (err 0)

b) when display was not activated
DP dual mode HDMI ID:  (err -6)

I know generally there can be a possibility that EDID is corrupted. But if this
will be the case, this problematical monitor should not work with other
computer (in my opinion only). But it works.
So I focus on err=-6 right now and ask experts like you for help.

I have attached 2 log files (both are dmesg with drm.debug=0xe extra kernel
parameter only)

attachment 1:
Dongle + Problematical monitor combination

attachment 2:
Dongle + Non-problematical TV combination

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