usb-device-{cdc, hid}: Fix handling of zero length OUT control xfers.

This fix relies on a corresponding change in the low-level USBDevice class.
Without the low-level change, HID and CDC devices may not work correctly at
all.

Zero length OUT control requests were being processed on the device but
stalling the endpoint so the host saw a failure (or hang followed by
failure).

Specifically:

- CDC set control line state and send break requests
- HID set idle or set protocol

This commit also simplifies HID set report logic (tested to still work even
when buffer size doesn't match report length).

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

Author: projectgus

micropython/usb/usb-device-cdc/usb/device/cdc.py

@@ -289,38 +289,32 @@ def on_interface_control_xfer(self, stage, request):
         bmRequestType, bRequest, wValue, wIndex, wLength = struct.unpack("BBHHH", request)
         recipient, req_type, req_dir = split_bmRequestType(bmRequestType)
 
-        # Only for the control interface
         if wIndex != self._c_itf:
-            return False
+            return False  # Only for the control interface (may be redundant check?)
+
+        if req_type != _REQ_TYPE_CLASS:
+            return False  # Unsupported request type
 
         if stage == _STAGE_SETUP:
-            if req_type == _REQ_TYPE_CLASS:
-                if bRequest == _SET_LINE_CODING_REQ:
-                    if wLength == len(self._line_coding):
-                        return self._line_coding
-                    return False  # wrong length
-                elif bRequest == _GET_LINE_CODING_REQ:
-                    return self._line_coding
-                elif bRequest == _SET_CONTROL_LINE_STATE:
-                    if wLength == 0:
-                        self._line_state = wValue
-                        if self.line_state_cb:
-                            self.line_state_cb(wValue)
-                        return b""
-                    else:
-                        return False  # wrong length
-                elif bRequest == _SEND_BREAK_REQ:
-                    if self.break_cb:
-                        self.break_cb(wValue)
-                    return b""
-
-        if stage == _STAGE_DATA:
-            if req_type == _REQ_TYPE_CLASS:
-                if bRequest == _SET_LINE_CODING_REQ:
-                    if self.line_coding_cb:
-                        self.line_coding_cb(self._line_coding)
-
-        return True
+            if bRequest in (_SET_LINE_CODING_REQ, _GET_LINE_CODING_REQ):
+                return self._line_coding  # Buffer to read or write
+
+            # Continue on other supported requests, stall otherwise
+            return bRequest in (_SET_CONTROL_LINE_STATE, _SEND_BREAK_REQ)
+
+        if stage == _STAGE_ACK:
+            if bRequest == _SET_LINE_CODING_REQ:
+                if self.line_coding_cb:
+                    self.line_coding_cb(self._line_coding)
+            elif bRequest == _SET_CONTROL_LINE_STATE:
+                self._line_state = wValue
+                if self.line_state_cb:
+                    self.line_state_cb(wValue)
+            elif bRequest == _SEND_BREAK_REQ:
+                if self.break_cb:
+                    self.break_cb(wValue)
+
+        return True  # allow DATA/ACK stages to complete normally
 
     def _wr_xfer(self):
         # Submit a new data IN transfer from the _wb buffer, if needed

micropython/usb/usb-device-hid/usb/device/hid.py

@@ -206,37 +206,25 @@ def on_interface_control_xfer(self, stage, request):
                     return bytes([self.idle_rate])
                 if bRequest == _REQ_CONTROL_GET_PROTOCOL:
                     return bytes([self.protocol])
+                if bRequest in (_REQ_CONTROL_SET_IDLE, _REQ_CONTROL_SET_PROTOCOL):
+                    return True
+                if bRequest == _REQ_CONTROL_SET_REPORT:
+                    return self._set_report_buf  # If None, request will stall
+            return False  # Unsupported request
+
+        if stage == _STAGE_ACK:
+            if req_type == _REQ_TYPE_CLASS:
                 if bRequest == _REQ_CONTROL_SET_IDLE:
                     self.idle_rate = wValue >> 8
-                    return b""
-                if bRequest == _REQ_CONTROL_SET_PROTOCOL:
+                elif bRequest == _REQ_CONTROL_SET_PROTOCOL:
                     self.protocol = wValue
-                    return b""
-                if bRequest == _REQ_CONTROL_SET_REPORT:
-                    # Return the _set_report_buf to be filled with the
-                    # report data
-                    if not self._set_report_buf:
-                        return False
-                    elif wLength >= len(self._set_report_buf):
-                        # Saves an allocation if the size is exactly right (or will be a short read)
-                        return self._set_report_buf
-                    else:
-                        # Otherwise, need to wrap the buffer in a memoryview of the correct length
-                        #
-                        # TODO: check this is correct, maybe TinyUSB won't mind if we ask for more
-                        # bytes than the host has offered us.
-                        return memoryview(self._set_report_buf)[:wLength]
-            return False  # Unsupported
-
-        if stage == _STAGE_DATA:
-            if req_type == _REQ_TYPE_CLASS:
-                if bRequest == _REQ_CONTROL_SET_REPORT and self._set_report_buf:
+                elif bRequest == _REQ_CONTROL_SET_REPORT:
                     report_id = wValue & 0xFF
                     report_type = wValue >> 8
                     report_data = self._set_report_buf
                     if wLength < len(report_data):
-                        # as above, need to truncate the buffer if we read less
-                        # bytes than what was provided
+                        # need to truncate the response in the callback if we got less bytes
+                        # than allowed for in the buffer
                         report_data = memoryview(self._set_report_buf)[:wLength]
                     self.on_set_report(report_data, report_id, report_type)