On Tue, Apr 10, 2018 at 09:05:07AM +0000, andrey.ara...@nixaid.com wrote:
> Dear Linux Kernel Devs,
> I have recently got a Lenovo ThinkVision X1 27" monitor, it is connected to my
> laptop over a USB-C cable (DisplayPort).
> This monitor has a built-in USB hub with a toggle button, when pressed it
> shows two options on the screen:
> Press USB Switch to toggle between:
> A) 3840x2160 UHD USB 2.0
> B) 1920x1080 FHD USB 3.0
> By default it is always set to FHD, which is why Linux sees the 1920x1080 as a
> maximum possible resolution.
> Whenever I am changing it to the UHD, Linux is not changing the resolution to
> 3840x2160, instead it sets to somewhere around 2560x####.
> To work this around, I am running the following commands manually:
> xrandr --newmode "3840x2160_60.00" 533.25  3840 3888 3920 4000  2160 2163 
> 2168 2222 +hsync -vsync
> xrandr --addmode DisplayPort-2 3840x2160_60.00
> xrandr --output DisplayPort-2 --mode 3840x2160_60.00
> Then, when I was trying to switch it back to FHD and again back to UHD,
> sometimes it causes a kernel panic. The panic also happened when I was
> plugging the cable in/out and back again. What I was able to spot is that the
> last unloaded kernel module was usbhid.
> Please advise, what can I try to help investigating this issue further?
> I have attached the output from "dmesg -T" command as "4.16.1-dmesg.txt" file.
> The logs are related to when the monitor was connected via a USB-C cable to a
> DisplayPort-2, the default resolution picked was FHD (USB 3.0) and then I have
> pressed the toggle button to use UHD (USB 2.0), then have applied the "xrandr"
> commands and have closed the lid of my laptop so I would be using my monitor
> as a primary display.

The board seems to support Thunderbold, however, in this case my guess is that
the monitor is actually using just the DP alternate mode (Thundebolt can pipe
DisplayPort protocol).

I'm guessing the problem is related to the DisplayPort lane counts. With the
highest resolutions you need all four lanes, but if you want to use USB3 with
USB Type-C connectors at the same time, two have to be allocated for USB3
leaving only two for DisplayPort allowing lower resolution. The problem is that
the GPU drivers need to know how many lanes the DisplayPort has in use. That
information will in normal case come from USB Type-C drivers. Unfortunately we
do not have support for that in Linux kernel yet, but I have made a proposal for
a solution.

Let's start by checking details of your board. Can you send us acpidump output?

        % acpidump -o <filename>

Also, please check the status of these acpi devices:

        % cat /sys/bus/acpi/devices/USBC*/status
        % cat /sys/bus/acpi/devices/INT3515*/status


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