Documenting other possible return value of hf_mailbox_send.
Change-Id: I5c8b81bd6cdc12ba346897e5cba036f9d302be34
diff --git a/inc/vmapi/hf/call.h b/inc/vmapi/hf/call.h
index 7de8160..7f229d2 100644
--- a/inc/vmapi/hf/call.h
+++ b/inc/vmapi/hf/call.h
@@ -93,6 +93,8 @@
* - 0, if the caller is a secondary VM
* - the ID of the vCPU to run to receive the message, if the caller is the
* primary VM.
+ * - HF_INVALID_VCPU if the caller is the primary VM and no vCPUs on the target
+ * VM are currently waiting to receive a message.
*/
static inline int64_t hf_mailbox_send(uint32_t vm_id, size_t size)
{
