xfree86: Fallback to first platform device as primary

When neither of the various bus implementations was able to find a
primary bus and device, fallback to using the platform bus as primary
bus and the first platform device as primary device.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Tested-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Keith Packard <keithp@keithp.com>
(cherry picked from commit 2f0183222b)
[hdegoede: backport to 1.16 which doesn't have syspath directly in OdevAttributes]
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Julien Cristau <jcristau@debian.org>

hw/xfree86/common/xf86Bus.c

@@ -210,6 +210,9 @@ xf86BusProbe(void)
 #if (defined(__sparc__) || defined(__sparc)) && !defined(__OpenBSD__)
     xf86SbusProbe();
 #endif
+#ifdef XSERVER_PLATFORM_BUS
+    xf86platformPrimary();
+#endif
 }
 
 /*

hw/xfree86/common/xf86platformBus.c

@@ -635,4 +635,21 @@ void xf86platformVTProbe(void)
         xf86PlatformReprobeDevice(i, xf86_platform_devices[i].attribs);
     }
 }
+
+void xf86platformPrimary(void)
+{
+    /* use the first platform device as a fallback */
+    if (primaryBus.type == BUS_NONE) {
+        xf86Msg(X_INFO, "no primary bus or device found\n");
+
+        if (xf86_num_platform_devices > 0) {
+            char *syspath = xf86_get_platform_attrib(0, ODEV_ATTRIB_SYSPATH);
+
+            primaryBus.id.plat = &xf86_platform_devices[0];
+            primaryBus.type = BUS_PLATFORM;
+
+            xf86Msg(X_NONE, "\tfalling back to %s\n", syspath);
+        }
+    }
+}
 #endif

hw/xfree86/common/xf86platformBus.h

@@ -77,6 +77,7 @@ extern _X_EXPORT int
 xf86PlatformMatchDriver(char *matches[], int nmatches);
 
 extern void xf86platformVTProbe(void);
+extern void xf86platformPrimary(void);
 #endif
 
 #endif