Could it be that there is a whitelist of display sizes aosp supports?
I’ve got a display with the resolution 780x350 and somehow the board does not display anything.
On other displays (1080p for example) it does work.
No idea but as a first step you could try turning on some of the drm.debug= features related to monitor detection and see if there is an obvious difference between working and broken displays (the 780x350 is weird enough that the display might not be sharing a sensible EDID with the display stack meaning the kernel doesn’t set up a display mode)
PS would also be interesting to know if this display works in the Debian releases…
Thank you for your feedback.
The Edid values fo the not-working display is all set. I also compared it with a monitor that works. All values are given. When I plug that non-working display via HDMI. Logcat does tell me:
E getActiveMode failed for display 4621278797924644728: No active mode
A HWC returned no active modepid-8137
First of all I have to know what is meant with “No active mode”. This seems to come from the HWComposer.cpp
I haven’t checked the code but I suspect it means that the kernel, having parsed the EDID, was unable to set up any display mode.
As mentioned setting up drm.debug appropriately gives you the deepest insight into what is going on (the kernel logs its EDID related decisions) but another quick check is to run ls /sys/class/drm/card* and compare the “enabled” and “modes” files between the good and bad cases.
If that shows the problem (e.g. that the display output is not enabled with the unusual monitor) the you’d need to go digging through the msm display driver (guided by the drm.debug messages) to find identify the problem.
Thank you for your hints Daniel.
I will follow them, and will give a feedback.
What I could test is, that it does work with a Ubuntu pc. Ubuntu can run this display. So it seems be a android specific problem. I will try to debug it, like your wrote.
@danielt Do you know, from where can I find information about the supported resolutions, timings, and frequencies for displays? Is there a comprehensive list or whitelist available?
No idea I’m afraid.
That’s the main reason I recommended testing the Debian images for the RB3 and, if it does reproduce there, experimenting with the drm.debug kernel options to get debug messages. Those are the tools I would use to find the info you asked about 
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