iwlwifi: mvm: provide helper to fetch the iwl_mvm_sta from sta_id

We somtimes need to fetch the iwl_mvm_sta structure from a
station index - provide a helper to do that.

Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
diff --git a/drivers/net/wireless/iwlwifi/mvm/mvm.h b/drivers/net/wireless/iwlwifi/mvm/mvm.h
index bf13c46..02e4bdc 100644
--- a/drivers/net/wireless/iwlwifi/mvm/mvm.h
+++ b/drivers/net/wireless/iwlwifi/mvm/mvm.h
@@ -595,6 +595,24 @@
 	       test_bit(IWL_MVM_STATUS_HW_CTKILL, &mvm->status);
 }
 
+static inline struct iwl_mvm_sta *
+iwl_mvm_sta_from_staid_protected(struct iwl_mvm *mvm, u8 sta_id)
+{
+	struct ieee80211_sta *sta;
+
+	if (sta_id >= ARRAY_SIZE(mvm->fw_id_to_mac_id))
+		return NULL;
+
+	sta = rcu_dereference_protected(mvm->fw_id_to_mac_id[sta_id],
+					lockdep_is_held(&mvm->mutex));
+
+	/* This can happen if the station has been removed right now */
+	if (IS_ERR_OR_NULL(sta))
+		return NULL;
+
+	return iwl_mvm_sta_from_mac80211(sta);
+}
+
 extern const u8 iwl_mvm_ac_to_tx_fifo[];
 
 struct iwl_rate_info {