usb-uhci: process uhci_handle_td return code via switch.

Restruct the uhci_handle_td return code processing to make the
control flow more clear and the code more readable.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/usb-uhci.c

@@ -1029,23 +1029,29 @@ static void uhci_process_frame(UHCIState *s)
             pci_dma_write(&s->dev, (link & ~0xf) + 4, &val, sizeof(val));
         }
 
-        if (ret < 0) {
-            /* interrupted frame */
-            break;
-        }
-
-        if (ret == 2 || ret == 1) {
-            DPRINTF("uhci: TD 0x%x %s. link 0x%x ctrl 0x%x token 0x%x qh 0x%x\n",
-                    link, ret == 2 ? "pend" : "skip",
-                    td.link, td.ctrl, td.token, curr_qh);
+        switch (ret) {
+        case -1: /* interrupted frame */
+            goto out;
 
+        case 1: /* goto next queue */
+            DPRINTF("uhci: TD 0x%x skip. "
+                    "link 0x%x ctrl 0x%x token 0x%x qh 0x%x\n",
+                    link, td.link, td.ctrl, td.token, curr_qh);
             link = curr_qh ? qh.link : td.link;
             continue;
-        }
 
-        /* completed TD */
+        case 2: /* got USB_RET_ASYNC */
+            DPRINTF("uhci: TD 0x%x async. "
+                    "link 0x%x ctrl 0x%x token 0x%x qh 0x%x\n",
+                    link, td.link, td.ctrl, td.token, curr_qh);
+            fprintf(stderr, "async td: link %x%s\n",
+                    td.link, is_valid(td.link) ? " valid" : "");
+            link = curr_qh ? qh.link : td.link;
+            continue;
 
-        DPRINTF("uhci: TD 0x%x done. link 0x%x ctrl 0x%x token 0x%x qh 0x%x\n", 
+        case 0: /* completed TD */
+            DPRINTF("uhci: TD 0x%x done. "
+                    "link 0x%x ctrl 0x%x token 0x%x qh 0x%x\n",
                     link, td.link, td.ctrl, td.token, curr_qh);
 
             link = td.link;
@@ -1068,10 +1074,16 @@ static void uhci_process_frame(UHCIState *s)
                     link    = qh.link;
                 }
             }
+            break;
+
+        default:
+            assert(!"unknown return code");
+        }
 
         /* go to the next entry */
     }
 
+out:
     s->pending_int_mask |= int_mask;
 }