Zoltán Böszörményi authored Feb 12, 2020 and Adam Jackson committed Feb 12, 2020

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 <zboszor@pr.hu>