uvcsink: Respond to control requests with proper error handling

The complete handling on the control interface is currently dead.
We return with EOPNOTSUPP for the caller to know that a response
to such requests is not valid. The host however may ask
control interface why these control requests were not available.

For this the UVC_VC_REQUEST_ERROR_CODE_CONTROL is used. As an overall
exception for the control interface we just always return 0x06 as
an response which is representing "not implemented".

This patch is a necessary feature to properly pass the UVC Functionality
Test of the USB3CV Compliance Software.

Fixes: 69c17461392d ('uvcgadget: Properly implement GET_INFO control responses')
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7524>

subprojects/gst-plugins-bad/sys/uvcgadget/gstuvcsink.c

@@ -640,6 +640,8 @@ gst_uvc_sink_init (GstUvcSink * self)
   gst_pad_set_query_function (self->sinkpad, gst_uvc_sink_query);
   gst_pad_set_event_function (self->sinkpad, gst_uvc_sink_event);
 
+  self->request_error_code = REQUEST_ERROR_CODE_NO_ERROR;
+
   self->cur_caps = gst_caps_new_empty ();
 }
 
@@ -985,6 +987,7 @@ gst_uvc_sink_change_state (GstElement * element, GstStateChange transition)
     case GST_STATE_CHANGE_PAUSED_TO_READY:
       gst_element_sync_state_with_parent (GST_ELEMENT (self->fakesink));
       gst_uvc_sink_remove_idle_probe (self);
+      self->request_error_code = REQUEST_ERROR_CODE_NO_ERROR;
       break;
     case GST_STATE_CHANGE_READY_TO_NULL:
       if (!gst_uvc_sink_unwatch (self))

subprojects/gst-plugins-bad/sys/uvcgadget/gstuvcsink.h

@@ -17,6 +17,9 @@
 
 G_BEGIN_DECLS GST_DEBUG_CATEGORY_EXTERN (uvcsink_debug);
 
+#define REQUEST_ERROR_CODE_NO_ERROR 0x0
+#define REQUEST_ERROR_CODE_INVALID_REQUEST 0x6
+
 #define GST_TYPE_UVCSINK (gst_uvc_sink_get_type())
 G_DECLARE_FINAL_TYPE (GstUvcSink, gst_uvc_sink, GST, UVCSINK, GstBin)
 
@@ -54,6 +57,8 @@ struct _GstUvcSink
 
   int control;
 
+  int request_error_code;
+
   /* probes */
   int buffer_peer_probe_id;
   int idle_probe_id;

subprojects/gst-plugins-bad/sys/uvcgadget/uvc.c

@@ -343,7 +343,7 @@ uvc_events_process_streaming (GstUvcSink * self, uint8_t req, uint8_t cs,
   return 0;
 }
 
-static void
+static int
 uvc_events_parse_control (GstUvcSink * self, uint8_t req,
     uint8_t cs, uint8_t entity_id, uint8_t len, struct uvc_request_data *resp)
 {
@@ -357,26 +357,50 @@ uvc_events_parse_control (GstUvcSink * self, uint8_t req,
     case 0:
       GST_DEBUG_OBJECT (self, "%s",
           uvc_video_control_interface_control_selector_name (cs));
-      break;
+      /*
+       * For ERROR_CODE_CONTROL requests we have to return not implemented so
+       * bail out gracefully here to properly send control is not
+       * currently implemented. (0x06) (4.2.1.2 Request Error Code Control)
+       */
+      if (cs == UVC_VC_REQUEST_ERROR_CODE_CONTROL) {
+        resp->data[0] = self->request_error_code;
+        resp->length = 1;
+
+        break;
+      }
+      goto error;
 
     case 1:
       GST_DEBUG_OBJECT (self, "%s: %s",
           uvc_camera_terminal_control_selector_name (cs),
           uvc_request_name (req));
-      break;
+      goto error;
 
     case 2:
       GST_DEBUG_OBJECT (self, "%s: %s",
           uvc_processing_unit_control_selector_name (cs),
           uvc_request_name (req));
-      break;
+      goto error;
 
     default:
       GST_DEBUG_OBJECT (self,
           "Unknown entity ID (0x%02x), CS: 0x%02x, Request %s (0x%02x)",
           entity_id, cs, uvc_request_name (req), req);
-      break;
+      goto error;
   }
+
+  self->request_error_code = REQUEST_ERROR_CODE_NO_ERROR;
+
+  return 0;
+
+error:
+
+  self->request_error_code = REQUEST_ERROR_CODE_INVALID_REQUEST;
+  /*
+   * Stall and don't response the control requests that are
+   * actually not implemented
+   */
+  return -EOPNOTSUPP;
 }
 
 static int
@@ -389,9 +413,8 @@ uvc_events_process_class (GstUvcSink * self,
     return -EINVAL;
 
   if (interface == UVC_STRING_CONTROL_IDX) {
-    uvc_events_parse_control (self, ctrl->bRequest, ctrl->wValue >> 8,
-        ctrl->wIndex >> 8, ctrl->wLength, resp);
-    return -EOPNOTSUPP;
+    return uvc_events_parse_control (self, ctrl->bRequest,
+        ctrl->wValue >> 8, ctrl->wIndex >> 8, ctrl->wLength, resp);
   } else if (interface == UVC_STRING_STREAMING_IDX) {
     return uvc_events_process_streaming (self, ctrl->bRequest,
         le16toh (ctrl->wValue) >> 8, resp);