[Bug 87917] [hsw] MST configuration not enabled automatically on boot

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=87917

Chris Wilson <chris at chris-wilson.co.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |intel-gfx-bugs at lists.freede
                   |                            |sktop.org
          Component|Driver/intel                |DRM/Intel
           Assignee|chris at chris-wilson.co.uk    |intel-gfx-bugs at lists.freede
                   |                            |sktop.org
            Product|xorg                        |DRI
            Summary|MST not being enabled on    |[hsw] MST configuration not
                   |Haswell host                |enabled automatically on
                   |                            |boot

--- Comment #1 from Chris Wilson <chris at chris-wilson.co.uk> ---
(In reply to Steven Noonan from comment #0)
> Created attachment 111587 [details]
> dmesg 3.18.1, unhappy MST
> 
> I've got a GIGABYTE Brix Pro i7-4770R box with a Mini DisplayPort output.
> Attached to that port I have a Dell UP2414Q 4K monitor, with DisplayPort 1.2
> mode enabled. On Windows I'm able to use the native MST-backed 60Hz 4K
> resolution without issues.
> 
> On Linux (3.18.1), I'm having troubles getting that to happen.
> 
> First of all, X11 is starting at 1024x768 resolution, and the kernel said
> this about it:
> 
> [    2.631515] [drm] Cannot find any crtc or sizes - going 1024x768

This is the crux of the issue, just that the state readback for MST is not yet
perfect and so we fail to inherit the initial state, if any.
>
> Once X11 is started, I'm able to see the two halves of the display in my KDE
> monitor preferences (DP1-8 and DP1-9, where DP1-9 is the left half of the
> display). I can also set both of them to 1920x2160 and configure the
> positioning such that the two halves are treated as separate monitor outputs
> side-by-side. But ideally this should be discovered as one 3840x2160
> monitor, on a single DisplayPort output. That would also make it so that my
> X11 WM would treat it as a single desktop.

So long as you appreciate that it is a single logical monitor backed by two 2
Display Ports, work is in progress to provide that level of automatic
configuration to the display managers.

> I've booted my kernel with drm.debug=6, and attached it for inspection.

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