<div dir="ltr"><div>Is there a reason we can't somehow "merge" the two CRTCs together into one virtual CRTC? Too difficult to modeset? </div></div><div class="gmail_extra"> <div class="gmail_quote"> On Thu, Jan 16, 2014 at 2:11 PM, Aaron Plattner <<a href="mailto:aplattner@nvidia.com" target="_blank">aplattner@nvidia.com</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> So, monitor manufacturers are starting to make high-resolution displays that consist of one LCD panel that appears to the PC as two. The one I've got is a Dell UP2414Q. It shows up to the PC as two DisplayPort 1.2 multistream devices that have the same GUID but different EDIDs. There's an extension block in the EDID that's supposed to indicate which side is the left tile and which is the right, though I haven't tried to decode it yet. The problem, obviously, is that applications (including some games) treat the two tiles as if they were completely separate monitors. Windows maximize to only half of the screen. My question is, how do we want to deal with these monitors? As far as I see it, we have four options: 1. Hide the presence of the second tile in the X server. Somehow combine the two tiles into a single logical output at the RandR protocol level. The X server would be responsible for setting up the right configuration to drive the logical output using the correct physical resources. 2. Hide the presence of the second tile in libXrandr. This would allow interested applications to query the real state of the hardware while also making it easier to do modesets on a per-monitor level rather than per-output. This could be exposed either as a new "simple" modeset API in libXrandr or similar, or by modifying the existing interface and having a new interface to punch through the façade and get at the real configuration, for clients that care. 3. Update every application that uses RandR 1.2. Applications can detect the presence of these monitors and deal with them themselves, but this might have poor adoption because programmers are a lazy bunch in general. 4. Do nothing and hope the problem goes away. Hopefully, the situation with current 4k monitors is temporary and we'll start seeing single-tile 4k displays soon, fixing the problem "forever". Until we get 8k tiled displays. If the real output devices are still exposed through the protocol, it might make sense to add new properties describing their relative positions to make it easier for clients to lay them out in the right order. This might be useful for power-walls too. The problem with the first two options is that driving these monitors consumes two crtcs. If we present them as a single output to applications, they'll make the assumption that they can just assign a single crtc to that output and use the remaining crtcs for something else. I suspect that deleting crtcs or otherwise marking them as used as a side effect of setting a mode on a different crtc is going to explode a lot of existing applications. ~~ Regardless of what we do about the current crop of 4k monitors, one feature I would like to add is a standardized OutputGroup property. Multiple outputs with the same value of OutputGroup should be considered (both by clients and the server) as a single logical monitor. This would affect the Xinerama information presented by rrxinerama.c, and window managers that use RandR 1.2 directly would be encouraged to consider output groups in their UI behavior. The X server could configure OutputGroups automatically when setting up the initial configuration based on the presence of tiled displays, and clients could reconfigure the groups at runtime to get different behavior if desired. Does this sound like a reasonable extension to RandR? -- Aaron _______________________________________________ <a href="mailto:xorg-devel@lists.x.org">xorg-devel@lists.x.org</a>: X.Org development Archives: <a href="http://lists.x.org/archives/xorg-devel" target="_blank">http://lists.x.org/archives/xorg-devel</a> Info: <a href="http://lists.x.org/mailman/listinfo/xorg-devel" target="_blank">http://lists.x.org/mailman/listinfo/xorg-devel</a></blockquote></div> -- Jasper </div>