[Bug 108502] Invalid encoder after hotplug

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108502

--- Comment #9 from Wolfgang Haupt <haupt.wolfgang at gmail.com> ---
(In reply to Ville Syrjala from comment #7)
> (In reply to Wolfgang Haupt from comment #4)
> > (In reply to Stanislav Lisovskiy from comment #3)
> > > (In reply to Lakshmi from comment #2)
> > > > Stan, any comments here?
> > > 
> > > So far I only had time to run the program attached. For me it shows
> > > everything correctly - when I have dock two DP MST ports connected it shows
> > > connectors and encoder ids are not 0. For disconnected ones it shows zeroes. 
> > > 
> > > However as you know we have some bugs, which are only reproducible with
> > > certain hardware, so nothing new here.
> > 
> > What you say is correct, the case I want to make is like the following:
> > 1) When nothing is connected it shows zeroes.
> > 2) Keep program running
> > 3) Plugin HDMI
> > 4) Stop program
> > 5) Start program -> encoders are still 0.
> > 
> > The state in (5) will not change no matter how often you stop/start the
> > program.
> > You need to unplug/replug HDMI again to make it work.
> > This happens on Kaby Lake for me.
> > 
> > 
> > To me it looks like an issue if a user space programm has a file handle to
> > /dev/dri/cardX and the state of HDMI goes from disconnected to connected.
> > 
> > Please let me know if you need further information.
> 
> The drm master is in charge of enabling/disabling displays. The first client
> to open the device node will automatically become the master. And afterwards
> as long as open fds remain fbdev/fbcon will not try to do anything with the
> displays. It's not clear from the above explanation whether all fds are
> getting closed or not. If they are not then the behaviour is as expected.
> 
> As far as hotplug support for kodi goes, you definitely don't want to rely
> on fbdev/fbcon to enable displays for you. You should be doing that
> yourself. fbdev might not even be enabled on the system.

(In reply to Lakshmi from comment #8)
> Wolfgang, can you address Ville's comment 7.

I wanted to answer that, but I don't understand the comment and lack knowledge
on how to respond properly.
As soon as I found the time to update my kernel to the latest drm-tip and see
if the issue
is still present, we can discuss it further.
I'm still looking for answers on how to properly support display hotplug in
DRM/KMS.
As we directly talk via libdrm and have no compositor, I tried to look at
weston's DRM/KMS backend, but
couldn't find reference code there as well.

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