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I'm having a curious issue with my setup. I've got two dell monitors daisy chained to my laptop, a Dell XPS 13 2015 (9343). I have displayport 1.2 enabled on the monitors to allow for the daisy-chaining. The curious thing is that if I have the displayport cable connected on boot, none of the external displays are detected. If I start X (I run openbox) still, no external displays are detected. If I disconnect the cable and reconnect, it does not detect the displays.
However, if I boot with the cable disconnected, wait until the login prompt (i don't have any display/login manager enabled) and then connect the cable, both monitors are detected and the login prompt is mirrored to all screens. If I then start X, they continue to work and I can use xrandr to mirror, extend etc.
But, if I ever have to reboot the machine, I have to disconnect the displayport prior to rebooting otherwise the displays will not be detected.
I've got the latest uefi/bios firmware (A05)
It's an Intel Broadwell-U Integrated Graphics chip with xf86-video-intel driver 1:2.99.917+478+gdf72bc5-2
I've tried with the latest kernel 4.2.2-1 and the lts kernel 4.1.10-2, both have the same issue. No extra kernel parameters or anything.
Just wondering if anyone has any insight on this, it would be greatly appreciated.
Thanks
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I should also add if I disable displayport 1.2 on the monitor, then the monitor is detected at boot with the cable connected as normal. but then, of course, there is no daisy-chaining so only the one monitor is available.
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updating to kernel 4.2.4-1 seems to have fixed the issue
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