Fix modesetting device matching through kmsdev device path

xf86platformProbeDev didn't check the device path, fix it.

This is a problem when trying to set up a non-PCI device via explicit xorg.conf.d configuration.

An USB DisplayLink device, being non-PCI was always set up as a GPU device assigned to screen 0 instead of a regular framebuffer, potentially having its own dedicated screen, despite such configuration as below. Only the relevant parts of the configuration are quoted, it's part of a larger context with an Intel chip that has 3 outputs:

  • DP1 connected to an LCD panel,
  • VGA1 connected to an external monitor,
  • HDMI1 unconnected and having no user visible connector

Section "ServerFlags" Option "AutoBindGPU" "false" EndSection


Section "Device" Identifier "Intel2" Driver "intel" BusID "PCI:0:2:0" Screen 2 Option "Monitor-HDMI1" "HDMI1" Option "ZaphodHeads" "HDMI1" EndSection

Section "Device" Identifier "UDL" Driver "modesetting" Option "kmsdev" "/dev/dri/card0" #BusID "usb:0:1.2:1.0" Option "Monitor-DVI-I-1" "DVI-I-1" Option "ShadowFB" "on" Option "DoubleShadow" "on" EndSection


Section "Screen" Identifier "SCREEN2" Option "AutoServerLayout" "on" Device "UDL" GPUDevice "Intel2" Monitor "Monitor-DVI-I-1" SubSection "Display" Modes "1024x768" Depth 24 EndSubSection EndSection

Section "ServerLayout" Identifier "LAYOUT" Option "AutoServerLayout" "on" Screen 0 "SCREEN" Screen 1 "SCREEN1" RightOf "SCREEN" Screen 2 "SCREEN2" RightOf "SCREEN1" EndSection

On the particular machine I was trying to set up an UDL device, I found the following structure was being used to match the device to a platform device while I was debugging the issue:

xf86_platform_devices[0] == Intel, /dev/dri/card1, primary platform device xf86_platform_devices[1] == UDL, /dev/dri/card0

devList[0] == "Intel0", ZaphodHeads: DP1 devList[1] == "Intel1", ZaphodHeads: VGA1 devList[2] == "UDL" devList[3] == "Intel2", ZaphodHeads: HDMI1 (intended GPU device to UDL)

When xf86platformProbeDev() matched the UDL device, the BusID check failed in both cases of:

  • BusID "usb:0:1.2:1.0" was specified
  • Option "kmsdev" "/dev/dri/card0" was specified

As a result, xf86platformProbeDev() went on to call probeSingleDevice() with xf86_platform_devices[0] and devList[2], resulting in the UDL device being set up as a GPU device assigned to the first screen instead of as a framebuffer on the third screen as the configuration specified.

Checking Option "kmsdev" in code code may be a layering violation. But the modesetting driver is actually part of the Xorg sources instead of being an external driver, so he "kmsdev" path knowledge may be used here.

Signed-off-by: Böszörményi Zoltán

Edited by Zoltán Böszörményi

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