shared/tinyusb: Fix dynamic USB control callbacks for wLength==0.

In the case where an OUT control transfer triggers with wLength==0 (i.e.
all data sent in the SETUP phase, and no additional data phase) the
callbacks were previously implemented to return b"" (i.e. an empty buffer
for the data phase).

However this didn't actually work as intended because b"" can't provide a
RW buffer (needed for OUT transfers with a data phase to write data into),
so actually the endpoint would stall.

The symptom was often that the device process the request (if processing
it in the SETUP phase when all information was already available), but the
host sees the endpoint stall and eventually returns an error.

This commit changes the behaviour so returning True from the SETUP phase of
a control transfer queues a zero length status response.

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

1 files changed, 10 insertions, 5 deletions

diff --git a/shared/tinyusb/mp_usbd_runtime.c b/shared/tinyusb/mp_usbd_runtime.c
index 0b4c79831..7ff7dd4ab 100644
--- a/shared/tinyusb/mp_usbd_runtime.c
+++ b/shared/tinyusb/mp_usbd_runtime.c
@@ -295,6 +295,7 @@ static bool runtime_dev_control_xfer_cb(uint8_t rhport, uint8_t stage, tusb_cont
     mp_obj_usb_device_t *usbd = MP_OBJ_TO_PTR(MP_STATE_VM(usbd));
     tusb_dir_t dir = request->bmRequestType_bit.direction;
     mp_buffer_info_t buf_info;
+    bool result;
 
     if (!usbd) {
         return false;
@@ -319,7 +320,7 @@ static bool runtime_dev_control_xfer_cb(uint8_t rhport, uint8_t stage, tusb_cont
 
     // Check if callback returned any data to submit
     if (mp_get_buffer(cb_res, &buf_info, dir == TUSB_DIR_IN ? MP_BUFFER_READ : MP_BUFFER_RW)) {
-        bool result = tud_control_xfer(USBD_RHPORT,
+        result = tud_control_xfer(USBD_RHPORT,
             request,
             buf_info.buf,
             buf_info.len);
@@ -328,17 +329,21 @@ static bool runtime_dev_control_xfer_cb(uint8_t rhport, uint8_t stage, tusb_cont
             // Keep buffer object alive until the transfer completes
             usbd->xfer_data[0][dir] = cb_res;
         }
-
-        return result;
     } else {
         // Expect True or False to stall or continue
+        result = mp_obj_is_true(cb_res);
 
-        if (stage == CONTROL_STAGE_ACK) {
+        if (stage == CONTROL_STAGE_SETUP && result) {
+            // If no additional data but callback says to continue transfer then
+            // queue a status response.
+            tud_control_status(rhport, request);
+        } else if (stage == CONTROL_STAGE_ACK) {
             // Allow data to be GCed once it's no longer in use
             usbd->xfer_data[0][dir] = mp_const_none;
         }
-        return mp_obj_is_true(cb_res);
     }
+
+    return result;
 }
 
 static bool runtime_dev_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t result, uint32_t xferred_bytes) {