feat(spmc): add FFA_RX_RELEASE handler

Enable a partition to release its RX buffer and the SPMC
to update the appropriate state tracking.

Signed-off-by: Marc Bonnici <marc.bonnici@arm.com>
Change-Id: I5fb6d92244b5ed5f032269b29b102aa874bf3ae3
diff --git a/services/std_svc/spm/el3_spmc/spmc_main.c b/services/std_svc/spm/el3_spmc/spmc_main.c
index 703d445..5dbc48d 100644
--- a/services/std_svc/spm/el3_spmc/spmc_main.c
+++ b/services/std_svc/spm/el3_spmc/spmc_main.c
@@ -1011,6 +1011,7 @@
 	case FFA_ID_GET:
 	case FFA_FEATURES:
 	case FFA_VERSION:
+	case FFA_RX_RELEASE:
 	case FFA_MSG_SEND_DIRECT_REQ_SMC32:
 	case FFA_MSG_SEND_DIRECT_REQ_SMC64:
 	case FFA_PARTITION_INFO_GET:
@@ -1145,6 +1146,31 @@
 			       handle, cookie, flags, target_id);
 }
 
+static uint64_t rx_release_handler(uint32_t smc_fid,
+				   bool secure_origin,
+				   uint64_t x1,
+				   uint64_t x2,
+				   uint64_t x3,
+				   uint64_t x4,
+				   void *cookie,
+				   void *handle,
+				   uint64_t flags)
+{
+	struct mailbox *mbox = spmc_get_mbox_desc(secure_origin);
+
+	spin_lock(&mbox->lock);
+
+	if (mbox->state != MAILBOX_STATE_FULL) {
+		spin_unlock(&mbox->lock);
+		return spmc_ffa_error_return(handle, FFA_ERROR_DENIED);
+	}
+
+	mbox->state = MAILBOX_STATE_EMPTY;
+	spin_unlock(&mbox->lock);
+
+	SMC_RET1(handle, FFA_SUCCESS_SMC32);
+}
+
 /*******************************************************************************
  * This function will parse the Secure Partition Manifest. From manifest, it
  * will fetch details for preparing Secure partition image context and secure
@@ -1573,6 +1599,10 @@
 						  x2, x3, x4, cookie, handle,
 						  flags);
 
+	case FFA_RX_RELEASE:
+		return rx_release_handler(smc_fid, secure_origin, x1, x2, x3,
+					  x4, cookie, handle, flags);
+
 	case FFA_MSG_WAIT:
 		return msg_wait_handler(smc_fid, secure_origin, x1, x2, x3, x4,
 					cookie, handle, flags);