usb-host: avoid libusb_set_configuration calls

Seems some devices become confused when we call
libusb_set_configuration().  So before calling the function check
whenever the device has multiple configurations in the first place, and
in case it hasn't (which is the case for the majority of devices) simply
skip the call as it will have no effect anyway.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 20190522094702.17619-4-kraxel@redhat.com

hw/usb/host-libusb.c

@@ -1225,19 +1225,21 @@ static void usb_host_set_address(USBHostDevice *s, int addr)
 
 static void usb_host_set_config(USBHostDevice *s, int config, USBPacket *p)
 {
-    int rc;
+    int rc = 0;
 
     trace_usb_host_set_config(s->bus_num, s->addr, config);
 
     usb_host_release_interfaces(s);
-    rc = libusb_set_configuration(s->dh, config);
-    if (rc != 0) {
-        usb_host_libusb_error("libusb_set_configuration", rc);
-        p->status = USB_RET_STALL;
-        if (rc == LIBUSB_ERROR_NO_DEVICE) {
-            usb_host_nodev(s);
+    if (s->ddesc.bNumConfigurations != 1) {
+        rc = libusb_set_configuration(s->dh, config);
+        if (rc != 0) {
+            usb_host_libusb_error("libusb_set_configuration", rc);
+            p->status = USB_RET_STALL;
+            if (rc == LIBUSB_ERROR_NO_DEVICE) {
+                usb_host_nodev(s);
+            }
+            return;
         }
-        return;
     }
     p->status = usb_host_claim_interfaces(s, config);
     if (p->status != USB_RET_SUCCESS) {