broadband-modem-mbim: account for race condition in quick hot swap case

On MBIM modems, when the SIM is ejected and re-inserted in a quick manner,
the state machine logic encounters a race condition and eventually, the
modem response for subscriber status is ignored. This change accounts
for that state transition without erroring out.

Fixes #672.

include/ModemManager-errors.h

@@ -102,6 +102,7 @@
  * @MM_CORE_ERROR_RETRY: Operation cannot yet be performed, retry later.
  * @MM_CORE_ERROR_EXISTS: Item already exists.
  * @MM_CORE_ERROR_WRONG_SIM_STATE: Operation cannot be executed in the current SIM state. Since 1.20.
+ * @MM_CORE_ERROR_RESET_AND_RETRY: Operation cannot yet be performed, reset the retry count and retry later. Since 1.22.
  *
  * Common errors that may be reported by ModemManager.
  *
@@ -123,6 +124,7 @@ typedef enum { /*< underscore_name=mm_core_error >*/
     MM_CORE_ERROR_RETRY           = 12, /*< nick=Retry         >*/
     MM_CORE_ERROR_EXISTS          = 13, /*< nick=Exists        >*/
     MM_CORE_ERROR_WRONG_SIM_STATE = 14, /*< nick=WrongSimState >*/
+    MM_CORE_ERROR_RESET_AND_RETRY = 15, /*< nick=ResetRetry    >*/
 } MMCoreError;
 
 /**

src/mm-broadband-modem-mbim.c

@@ -1585,10 +1585,13 @@ unlock_required_subscriber_ready_state_ready (MbimDevice   *device,
     g_autoptr(MbimMessage)     response = NULL;
     GError                    *error = NULL;
     MbimSubscriberReadyState   ready_state = MBIM_SUBSCRIBER_READY_STATE_NOT_INITIALIZED;
+    MbimSubscriberReadyState   prev_ready_state = MBIM_SUBSCRIBER_READY_STATE_NOT_INITIALIZED;
 
     ctx = g_task_get_task_data (task);
     self = g_task_get_source_object (task);
 
+    /* hold on to the previous ready_state value to determine if the retry logic needs to be reset. */
+    prev_ready_state = self->priv->enabled_cache.last_ready_state;
     /* reset to the default if any error happens */
     self->priv->enabled_cache.last_ready_state = MBIM_SUBSCRIBER_READY_STATE_NOT_INITIALIZED;
 
@@ -1671,9 +1674,21 @@ unlock_required_subscriber_ready_state_ready (MbimDevice   *device,
             else
                 g_task_return_new_error (task, MM_CORE_ERROR, MM_CORE_ERROR_FAILED,
                                          "Error waiting for SIM to get initialized");
-        } else
+        } else {
-            g_task_return_new_error (task, MM_CORE_ERROR, MM_CORE_ERROR_RETRY,
+            /* Start the retry process from the top if the SIM state changes from
+             * MBIM_SUBSCRIBER_READY_STATE_SIM_NOT_INSERTED to
+             * MBIM_SUBSCRIBER_READY_STATE_NOT_INITIALIZED
+             * This will address the race condition that occurs during rapid hotswap. */
+            gboolean retry_reset_needed = FALSE;
+
+            if (prev_ready_state == MBIM_SUBSCRIBER_READY_STATE_SIM_NOT_INSERTED &&
+                ready_state == MBIM_SUBSCRIBER_READY_STATE_NOT_INITIALIZED)
+                retry_reset_needed = TRUE;
+            g_task_return_new_error (task,
+                                     MM_CORE_ERROR,
+                                     retry_reset_needed ? MM_CORE_ERROR_RESET_AND_RETRY : MM_CORE_ERROR_RETRY,
                                      "SIM not ready yet (retry)");
+        }
         g_object_unref (task);
         return;
     }

src/mm-iface-modem.c

@@ -604,6 +604,12 @@ load_unlock_required_ready (MMIfaceModem *self,
             return;
         }
 
+        /* If the error indicates that retry logic needs to be reset... reset the retry count to 0 */
+        if (g_error_matches (error, MM_CORE_ERROR, MM_CORE_ERROR_RESET_AND_RETRY)) {
+            ctx->retries = 0;
+            mm_obj_info (self, "restarting unlock required check");
+        }
+
         /* For the remaining ones, retry if possible */
         if (ctx->retries < ctx->max_retries) {
             ctx->retries++;