Hi All,
My
work recently updated our laptops to a Dell Lattitude E7450 laptop and
accompanying Dell E-Port plus advanced docking station. The machine has
Broadwell
Core I7 processor and integrated graphics. I've tried the latest
Ubuntu 15.10 (kernel version 4.2.0-25) with updated drivers from
01.org, and also running Linux Mint 17.3 based on the 14.4 Ubuntu LTS
release, which runs LInux kernel version 3.19.0-32.
I
have a 32" external 4k monitor connected to it through DP/miniDP cable.
I have checked that the monitor is set up to use DP 1.2 protocol.
The
problem is that when I connect the monitor through the dock using a DP
cable, the monitor can't do 4k resolution. It tops out at 2560x1440 at
60Hz. However, if I connect the monitor directly to the laptop (with or
without the laptop being on the dock), it can drive the full 4k@60Hz.
Moreover, the laptop is able to drive the full 4k resolution on the
Windows 7 operating system, so the issue is definitely some device
driver related. Needless to say, I do not use Windows at all. Note that
I've tried using xrandr on the command line, and also through the GUI
widget that Ubuntu provides.
When ever I connect/disconnect a monitor, I do get a bunch of warnings about interrupt controller, and FIFO underruns.
Jan 25 13:03:53 XXXX kernel: [ 536.304816] [drm:gen8_irq_handler [i915_bpo]] *ERROR* The master control interrupt lied (SDE)!
....
....
Jan
25 11:41:27 XXXX kernel: [26659.784376]
[drm:intel_cpu_fifo_underrun_irq_handler [i915_bpo]] *ERROR* CPU pipe B
FIFO underrun
Any help in resolving this would be appreciated. Is there a pointer to an existing bug report/mailing
list email? I am sure I'll soon get tired of the two step process of
plonking down the laptop on the dock, and then additionally connecting
the display cable to the monitor.
Thanks in advance,
Pankaj
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