[Bug 106529] Kernels 4.16+ confuses KDE wrt what the primary display is when waking up multiple displays

[Bug 106529] Kernels 4.16+ confuses KDE wrt what the primary display is when waking up multiple displays

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https://bugs.freedesktop.org/show_bug.cgi?id=106529

            Bug ID: 106529
           Summary: Kernels 4.16+ confuses KDE wrt what the primary
                    display is when waking up multiple displays
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: mariusz.g.mazur@gmail.com

Created attachment 139577
  --> https://bugs.freedesktop.org/attachment.cgi?id=139577&action=edit
ubuntu's 4.15 dmesg with amdgpu.dc_log=1

It appears that the display-handling code in 4.15+ (including 4.17-rc5) marks
any display not fully woken up as disconnected or something to that effect. So
when I have multiple monitors and they get woken up from sleep (doesn't matter
whether the computer was suspended or just idle for a long period), and my
primary display wakes up slower than the any of the other displays (and it
does), then for a few hundred ms KDE tries to change the primary display to the
one that first woke up (I'm guessing it thinks that's the only one available),
then changes its mind a bit later, when all displays wake up.

End result looks like crap and is not usable, since all my windows get
displaced. Here's how it looks like in practice:

Setup:
Radeon RX 560
Primary display: bottom right, displayport, on
Secondary display 1: left, hdmi, on
Secondary display 2: top right, dvi, off

Video of how it used to work, using 4.4.15:
https://www.youtube.com/watch?v=h7nMYbm5ZxU
Note how even though the left (secondary) display wakes up first, both
instantly display their proper desktops.

Video of how it works with ubuntu 18.04's default 4.15 kernel/4.16.7/4.17-rc5:
https://www.youtube.com/watch?v=VdVFNXPszSI
Note how when the left (secondary) display wakes up first, KDE decides that
this is probably the only display available, so tries to switch the primary
desktop to it, then a split second later the bottom right wakes up and KDE
knows *that* should be the primary according to the config, so it switches
back.

Attached is dmesg from ubuntu's 4.15 with dc_log=1. I put the computer to
sleep, then wake it up and get the behavior like in the video.

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[Bug 106529] Kernels 4.16+ confuse KDE wrt what the primary display is when waking up multiple displays

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https://bugs.freedesktop.org/show_bug.cgi?id=106529

Mariusz Mazur <mariusz.g.mazur@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Kernels 4.16+ confuses KDE  |Kernels 4.16+ confuse KDE
                   |wrt what the primary        |wrt what the primary
                   |display is when waking up   |display is when waking up
                   |multiple displays           |multiple displays

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[Bug 106529] Kernels 4.16+ confuse KDE wrt what the primary display is when waking up multiple displays

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https://bugs.freedesktop.org/show_bug.cgi?id=106529

Michel Dänzer <michel@daenzer.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
 Attachment #139577|text/x-log                  |text/plain
          mime type|                            |

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[Bug 106529] dc=1 kernels somehow trigger a disconnect of an lg ultrawide monitor during DP link training while attempting a wakeup

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https://bugs.freedesktop.org/show_bug.cgi?id=106529

Mariusz Mazur <mariusz.g.mazur@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Kernels 4.16+ confuse KDE   |dc=1 kernels somehow
                   |wrt what the primary        |trigger a disconnect of an
                   |display is when waking up   |lg ultrawide monitor during
                   |multiple displays           |DP link training while
                   |                            |attempting a wakeup

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[Bug 106529] dc=1 kernels somehow trigger a disconnect of an lg ultrawide monitor during DP link training while attempting a wakeup

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https://bugs.freedesktop.org/show_bug.cgi?id=106529

--- Comment #1 from Mariusz Mazur <mariusz.g.mazur@gmail.com> ---
I've tried the same thing with only the DP ultrawide monitor connected and got
the same issue. dc logs, reading code and some kernel tracers (ftrace) on DC
link training code basically tell me that the important part is this:

21:23:16 [drm] [LKTN]        [DP][ConnIdx:0] RBRx4 pass VS=2, PE=1^
21:23:16 [drm] link=0, dc_sink_in=          (null) is now Disconnected
21:23:18 [drm] [LKTN]        [DP][ConnIdx:0] HBRx4 pass VS=1, PE=0^
21:23:18 [drm] link=0, dc_sink_in=00000000dbbee48e is now Connected
21:23:18 [drm] [LKTN]        [DP][ConnIdx:0] RBRx4 pass VS=1, PE=1^

Whatever's going on with the first attempt at link training, it ends up with
the monitor disconnecting (not sure if deliberately or by causing some error in
the monitor; didn't dive deep enough into the code).

Pre-DC codepaths did not have an issue like this at all until Michel Dänzer
created this patch: https://patchwork.freedesktop.org/patch/209464/ for bug
105308 thereby introducing a problem with the same effects (DC monitor gets
disconnected on wakeup, which on multi-display causes issues) via a quite
different approach (a deliberate DRM_MODE_DPMS_OFF & ON). But that should be a
separate bug, I think.

And since Michel's patch got applied to all the kernels, the effect is that on
any up to date 4.15+ kernel the same issue shows up whether you're doing dc=1
or dc=0, while the actual code paths causing it are different. (Which made this
a PITA to figure out.)

Anyway, since I know nothing about DP link training and how to fix code
relating to it, I've just bought a DP->HDMI cable thus "fixing" my problem
entirely (including the second issue of a 2s lag with DP audio).

Hopefully someone in the future, a future man so to speak, will fix this issue
eventually. Cause currently DP support is quite bad, it seems.

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[Bug 106529] dc=1 kernels somehow trigger a disconnect of an lg ultrawide monitor during DP link training while attempting a wakeup

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https://bugs.freedesktop.org/show_bug.cgi?id=106529

--- Comment #2 from Michel Dänzer <michel@daenzer.net> ---
(In reply to Mariusz Mazur from comment #1)
> Pre-DC codepaths did not have an issue like this at all until Michel Dänzer
> created this patch: https://patchwork.freedesktop.org/patch/209464/ for bug
> 105308 thereby introducing a problem with the same effects (DC monitor gets
> disconnected on wakeup, which on multi-display causes issues) via a quite
> different approach (a deliberate DRM_MODE_DPMS_OFF & ON). But that should be
> a separate bug, I think.

FWIW, that change should have no direct effect on whether the display is
considered connected or disconnected. The only change is that when the driver
is notified that a DP display is "disconnected" (which can also happen without
a physical disconnection, e.g. if the display is turned off), it doesn't
immediately turn off the GPU's DP source anymore, but waits until either
userspace asks to turn it off, or it gets notified that a display is
"connected" again. Both "disconnect" / "connect" hotplug events are sent to
userspace before and after this change. I suspect that immediately turning off
the DP source simply happened to delay sending the "disconnect" hotplug event
to userspace enough to avoid the issue on your system.

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[Bug 106529] dc=1 kernels somehow trigger a disconnect of an lg ultrawide monitor during DP link training while attempting a wakeup

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https://bugs.freedesktop.org/show_bug.cgi?id=106529

--- Comment #3 from Mariusz Mazur <mariusz.g.mazur@gmail.com> ---
dc=1 codepath has the problem occur 100%  of the times the display wakes up
(iirc).

dc=0 with your patch does not. It happens regularly, but not 100% of the times.
Which I guess does indicate there's some timing issues involved.

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[Bug 106529] dc=1 kernels somehow trigger a disconnect of an lg ultrawide monitor during DP link training while attempting a wakeup

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https://bugs.freedesktop.org/show_bug.cgi?id=106529

--- Comment #4 from Alex Deucher <alexdeucher@gmail.com> ---
I suspect it may have something to do with the pulse timing from the monitor. 
Long pulses are for connect/disconnect events and short pulses are a feedback
mechanism for the monitor to the driver.  I suspect the monitor is sending a
short pulse that the driver is interpreting as a long pulse.

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[Bug 106529] dc=1 kernels somehow trigger a disconnect of an lg ultrawide monitor during DP link training while attempting a wakeup

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https://bugs.freedesktop.org/show_bug.cgi?id=106529

--- Comment #5 from Michel Dänzer <michel@daenzer.net> ---
Maybe one thing we could do is delaying the sending of the disconnect hotplug
event to userspace by some time (though at most until the next connect hotplug
event).

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[Bug 106529] dc=1 kernels somehow trigger a disconnect of an lg ultrawide monitor during DP link training while attempting a wakeup

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https://bugs.freedesktop.org/show_bug.cgi?id=106529

Martin Peres <martin.peres@free.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |MOVED

--- Comment #6 from Martin Peres <martin.peres@free.fr> ---
-- GitLab Migration Automatic Message --

This bug has been migrated to freedesktop.org's GitLab instance and has been
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You can subscribe and participate further through the new bug through this link
to our GitLab instance: https://gitlab.freedesktop.org/drm/amd/issues/386.

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