DisplayServer (Linux): support --ds-force-drm sysfs-only

src/detection/displayserver/linux/displayserver_linux.c

@@ -10,7 +10,7 @@ void ffConnectDisplayServerImpl(FFDisplayServerResult* ds)
     ffStrbufInit(&ds->dePrettyName);
     ffListInitA(&ds->displays, sizeof(FFDisplayResult), 4);
 
-    if (!instance.config.general.dsForceDrm)
+    if (instance.config.general.dsForceDrm == FF_DS_FORCE_DRM_TYPE_FALSE)
     {
         //We try wayland as our preferred display server, as it supports the most features.
         //This method can't detect the name of our WM / DE

src/detection/displayserver/linux/drm.c

@@ -285,8 +285,11 @@ static const char* drmConnectLibdrm(FFDisplayServerResult* result)
 void ffdsConnectDrm(FFDisplayServerResult* result)
 {
     #ifdef FF_HAVE_DRM
-    if (drmConnectLibdrm(result) == NULL)
-        return;
+    if (instance.config.general.dsForceDrm != FF_DS_FORCE_DRM_TYPE_SYSFS_ONLY)
+    {
+        if (drmConnectLibdrm(result) == NULL)
+            return;
+    }
     #endif
 
     drmParseSysfs(result);