Issues with USB-C external monitors
Ali Abdallah
ali.abdallah at suse.com
Wed Dec 2 10:28:46 UTC 2020
On 01.12.2020 17:10, myfreeweb wrote:
> devd (really drm in the kernel) provides hotplug events (system DRM, type HOTPLUG).
> libudev-devd translates these to UD_ACTION_HOTPLUG.
> This works well with wlroots compositors at least.
> How xorg does this I have no idea, as I don't use xorg.
> If your xorg is built with DEVD instead of UDEV option, it shouldn't work, I don't recall anyone adding support for that there.
> With UDEV it might work?
Actually Xorg on FreeBSD with UDEV is compiled with
--disable-config-udev-kms, thus the server never calls:
udev_monitor_filter_add_match_subsystem_devtype
for GPU devices, and thus libudev-devd doesn't forward kms events to the
server. Actually Xorg doesn't even process them, even if the filter check
is bypassed in libudev-devd (udev-monitor.c:261).
Basically Xorg is missing bsd platform code for drm devices, on Linux
the code that implements that can be found in:
hw/xfree86/os-support/linux/lnx_platform.c
Compiling the server with --enable-config-udev-kms, the server expects
to have the following functions implemented
xf86PlatformReprobeDevice, xf86PlatformDeviceProbe, DeleteGPUDeviceRequest and
xf86PlatformDeviceCheckBusID.
Those are fairly easy to implement to enable Xorg to listen to
libudev-devd drm events and to re-configure the drm connectors. I have
already some scratch code, will test more and probably send upstream.
I will probably also add devd code for that, as I use xorg server
with devd on my FreeBSD 12.x machines.
Thanks,
Ali
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