am7xxx-modeswitch: set USB configuration following libusb documentation

For the details see: http://libusb.sourceforge.net/api-1.0/caveats.html

diff --git a/examples/am7xxx-modeswitch.c b/examples/am7xxx-modeswitch.c
index b431084..1230bd4 100644 (file)
--- a/examples/am7xxx-modeswitch.c
+++ b/examples/am7xxx-modeswitch.c
@@ -35,6 +35,7 @@ int main(void)
 {
        int ret;
        libusb_device_handle *usb_device;
+       int current_configuration;
        unsigned int len;
        int transferred;
 
@@ -56,15 +57,26 @@ int main(void)
                goto out;
        }
 
-       ret = libusb_set_configuration(usb_device, AM7XXX_STORAGE_CONFIGURATION);
+       current_configuration = -1;
+       ret = libusb_get_configuration(usb_device, &current_configuration);
        if (ret < 0) {
-               fprintf(stderr, "libusb_set_configuration failed: %s\n",
+               fprintf(stderr, "libusb_get_configuration failed: %s\n",
                        libusb_error_name(ret));
-               fprintf(stderr, "Cannot set configuration %hhu\n",
-                       AM7XXX_STORAGE_CONFIGURATION);
                goto out_libusb_close;
        }
 
+       if (current_configuration != AM7XXX_STORAGE_CONFIGURATION) {
+               ret = libusb_set_configuration(usb_device,
+                                              AM7XXX_STORAGE_CONFIGURATION);
+               if (ret < 0) {
+                       fprintf(stderr, "libusb_set_configuration failed: %s\n",
+                               libusb_error_name(ret));
+                       fprintf(stderr, "Cannot set configuration %hhu\n",
+                               AM7XXX_STORAGE_CONFIGURATION);
+                       goto out_libusb_close;
+               }
+       }
+
        libusb_set_auto_detach_kernel_driver(usb_device, 1);
 
        ret = libusb_claim_interface(usb_device, AM7XXX_STORAGE_INTERFACE);
@@ -76,6 +88,24 @@ int main(void)
                goto out_libusb_close;
        }
 
+       /* Checking that the configuration has not changed, as suggested in
+        * http://libusb.sourceforge.net/api-1.0/caveats.html
+        */
+       current_configuration = -1;
+       ret = libusb_get_configuration(usb_device, &current_configuration);
+       if (ret < 0) {
+               fprintf(stderr, "libusb_get_configuration after claim failed: %s\n",
+                       libusb_error_name(ret));
+               goto out_libusb_release_interface;
+       }
+
+       if (current_configuration != AM7XXX_STORAGE_CONFIGURATION) {
+               fprintf(stderr, "libusb configuration changed (expected: %hhu, current: %hhu\n",
+                       AM7XXX_STORAGE_CONFIGURATION, current_configuration);
+               ret = -EINVAL;
+               goto out_libusb_release_interface;
+       }
+
        len = sizeof(switch_command);
        transferred = 0;
        ret = libusb_bulk_transfer(usb_device, AM7XXX_STORAGE_OUT_EP,