xfree86: Try harder to find atleast 1 non GPU Screen

If we did not find any non GPU Screens, try again ignoring the notion
of any video devices being the primary device. This fixes Xorg exiting
with a "no screens found" error when using virtio-vga in a
virtual-machine and when using a device driven by simpledrm.

This is a somewhat ugly solution, but it is the best I can come up with
without major surgery to the bus and probe code.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

hw/xfree86/common/xf86.h

@@ -55,6 +55,7 @@
 extern _X_EXPORT int xf86DoConfigure;
 extern _X_EXPORT int xf86DoShowOptions;
 extern _X_EXPORT Bool xf86DoConfigurePass1;
+extern _X_EXPORT Bool xf86ProbeIgnorePrimary;
 extern _X_EXPORT Bool xorgHWAccess;
 
 extern _X_EXPORT DevPrivateKeyRec xf86ScreenKeyRec;

hw/xfree86/common/xf86Bus.c

@@ -117,14 +117,34 @@ xf86BusConfig(void)
     int i, j;
 
     /*
-     * Now call each of the Probe functions.  Each successful probe will
+     * 3 step probe to (hopefully) ensure that we always find at least 1
-     * result in an extra entry added to the xf86Screens[] list for each
+     * (non GPU) screen:
-     * instance of the hardware found.
+     *
+     * 1. Call each drivers probe function normally,
+     *    Each successful probe will result in an extra entry added to the
+     *    xf86Screens[] list for each instance of the hardware found.
      */
     for (i = 0; i < xf86NumDrivers; i++) {
         xf86CallDriverProbe(xf86DriverList[i], FALSE);
     }
 
+    /*
+     * 2. If no Screens were found, call each drivers probe function with
+     *    ignorePrimary = TRUE, to ensure that we do actually get a
+     *    Screen if there is atleast one supported video card.
+     */
+    if (xf86NumScreens == 0) {
+        xf86ProbeIgnorePrimary = TRUE;
+        for (i = 0; i < xf86NumDrivers && xf86NumScreens == 0; i++) {
+            xf86CallDriverProbe(xf86DriverList[i], FALSE);
+        }
+        xf86ProbeIgnorePrimary = FALSE;
+    }
+
+    /*
+     * 3. Call xf86platformAddGPUDevices() to add any additional video cards as
+     *    GPUScreens (GPUScreens are only supported by platformBus drivers).
+     */
     for (i = 0; i < xf86NumDrivers; i++) {
         xf86platformAddGPUDevices(xf86DriverList[i]);
     }

hw/xfree86/common/xf86Globals.c

@@ -152,6 +152,7 @@ XF86ConfigPtr xf86configptr = NULL;
 Bool xf86Resetting = FALSE;
 Bool xf86Initialising = FALSE;
 Bool xf86DoConfigure = FALSE;
+Bool xf86ProbeIgnorePrimary = FALSE;
 Bool xf86DoShowOptions = FALSE;
 DriverPtr *xf86DriverList = NULL;
 int xf86NumDrivers = 0;

hw/xfree86/common/xf86pciBus.c

@@ -352,6 +352,10 @@ xf86ComparePciBusString(const char *busID, int bus, int device, int func)
 Bool
 xf86IsPrimaryPci(struct pci_device *pPci)
 {
+    /* Add max. 1 screen for the IgnorePrimary fallback path */
+    if (xf86ProbeIgnorePrimary && xf86NumScreens == 0)
+        return TRUE;
+
     if (primaryBus.type == BUS_PCI)
         return pPci == primaryBus.id.pci;
 #ifdef XSERVER_PLATFORM_BUS

hw/xfree86/common/xf86platformBus.c

@@ -114,6 +114,10 @@ xf86_find_platform_device_by_devnum(int major, int minor)
 static Bool
 xf86IsPrimaryPlatform(struct xf86_platform_device *plat)
 {
+    /* Add max. 1 screen for the IgnorePrimary fallback path */
+    if (xf86ProbeIgnorePrimary && xf86NumScreens == 0)
+        return TRUE;
+
     if (primaryBus.type == BUS_PLATFORM)
         return plat == primaryBus.id.plat;
 #ifdef XSERVER_LIBPCIACCESS