On Fri, Jun 26, 2020 at 10:25:45AM +0100, Daniel Stone wrote: > Hi, > > On Fri, 26 Jun 2020 at 10:00, Pekka Paalanen <ppaalanen@xxxxxxxxx> wrote: > > On Thu, 25 Jun 2020 12:44:36 +0200 Daniel Vetter <daniel@xxxxxxxx> wrote: > > > Maybe an aside, but the guideline is for autoconfiguration: > > > - Light up everything that has connector status connected. > > > - If nothing has that status, try to light up the connectors with > > > status "unknown". > > > > > > This is only really relevant on older platforms, mostly for VGA and > > > somewhat for dvi outputs. > > > > > > Maybe another thing we should put down somewhere in the uapi docs ... > > > > As I had no idea what "unknown" means or when it can happen, I assumed > > that it must mean "the hardware cannot know". If the hardware cannot > > know, then I certainly will not be trying to enable that, unless > > explicitly configured to do so. Having a phantom output is worse than > > having a real output that does not light up, because it's not obvious at > > first with phantom output that anything is wrong. You may just be > > wondering where your windows disappear, or where did you mouse cursor > > go, or why you see a wallpaper but no login dialog, etc. > > How about a refinement of Dan's suggestion, proceeding down this > logical order and breaking if true: > - ignore all disconnected outputs > - if any outputs are connected, ignore all unknown outputs > - if only one output is unknown, use only that output (with default > mode if need be) > - if any outputs are unknown but have EDID present, use only those outputs > - at this point, we have multiple unknown outputs with no EDID - break > and demand explicit user configuration EDID present generally means the status will be "connected". So not much of a refined. I'd say if you have multiple unknown, use a cloned config to avoid the "windows are disappearing" problem. Which is also what fbcon does, and iirc also -modesetting by default. But the most important part is to not light up "unknown" outputs if there's another output with a solid "connected". That avoids the problems Pekka points out, phantom outputs are bad. Really no need to refine beyond that, since imo that's a kernel bug. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
