Re: Issues with USB-C external monitors

On 12/1/20 2:14 PM, Ali Abdallah wrote:
> Hello,
> 
> I have a T495 with a USB-C docking station with two external monitors,
> running current to get the vega 10 amdgpu to work.
> 
> When the power is lost for on the USB-C dock, then the X server looses
> all external monitors. They appear as disconnected after running xrandr
> and I cannot figure out a way to bring them back without killing my
> current session and start X again, but that is very annoying...
> 
> I tried to debug the issue and I'm pretty sure that the X server on
> FreeBSD is not reconfiguring the drm connectors automatically.
> 
> Let's say I have DP-4 as external connector, when the power is lost,
> DP-4 disappears, when the power is back, DP-4 re-appear again but in
> unknown status.
> 
> $ sysctl sys.class.drm | grep DP-4
> sys.class.drm.card0-DP-4.modes:
> sys.class.drm.card0-DP-4.dpms: Off
> sys.class.drm.card0-DP-4.enabled: disabled
> sys.class.drm.card0-DP-4.status: unknown
> 
> Now just running a simple libdrm code to rescan the connectors:
> 
> __snippet__
> res = drmModeGetResources(fd);
> for (int i = 0; i < res->count_connectors; ++i) {
>     conn = drmModeGetConnector(fd, res->connectors[i]);
> 
> After running the above code, the drm stack is somehow triggered to
> re-read the DP-4.status, which appears now to be connected, but not
> configured.
> 
> $ sysctl sys.class.drm | grep DP-4
> sys.class.drm.card0-DP-4.modes: 1920x1080
> sys.class.drm.card0-DP-4.dpms: Off
> sys.class.drm.card0-DP-4.enabled: disabled
> sys.class.drm.card0-DP-4.status: connected
> 
> I didn't dig further to see if I can trigger the X server to re-scan drm
> connectors and eventually remove those that vanished, and add newly
> detected connectors. On Linux that seems to work automatically.
> 
> Any thoughts?

There is missing code in the kernel to handle USB-C PCI express 
attach/detach. CC'ing Scott Long.

--HPS