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 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. I've booted my kernel with drm.debug=6, and attached it for inspection.
(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.
The EFI BIOS doesn't seem to much like the 4K display either, as it starts up in a tiny display mode. GRUB2 also can't figure out what video modes are available. In the meantime I suppose I could figure out how to get Xinerama working in order for it to be treated as a single screen. Never had to touch Xinerama before though, and all the guides I see online are for ancient X versions that required an xorg.conf (and thus have tons of extra cruft in them, so it'll be interesting trying to figure out the minimal configuration necessary).
Timeout, closing. Please reopen if the problem persists with latest kernels.
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