greybus: use operation type 0 to signal incoming data

When incoming data is going to be handled as a request, we create a
new operation whose request buffer will hold the received data.
There is no need to initialize the message header in such a request
buffer because it will be immediately overwritten.

Use operation type value of 0x00 in gb_operation_create_common()
to signal that we are creating an incoming operation, and therefore
do not need to initialize the request message header.  This allows
us to get rid of the Boolean "outgoing" parameter.

As a result, we can stop supplying the "type" parameter to both
gb_operation_create_incoming() and gb_connection_recv_request().

Update the header comments for gb_operation_message_alloc() and
gb_operation_create_common().
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/staging/greybus/operation.c

@@ -302,12 +302,14 @@ gb_hd_message_find(struct greybus_host_device *hd, void *header)
 }
 
 /*
- * Allocate a message to be used for an operation request or
- * response.  For outgoing messages, both types of message contain a
- * common header, which is filled in here.  Incoming requests or
- * responses also contain the same header, but there's no need to
- * initialize it here (it'll be overwritten by the incoming
- * message).
+ * Allocate a message to be used for an operation request or response.
+ * Both types of message contain a common header.  The request message
+ * for an outgoing operation is outbound, as is the response message
+ * for an incoming operation.  The message header for an outbound
+ * message is partially initialized here.
+ *
+ * The headers for inbound messages don't need to be initialized;
+ * they'll be filled in by arriving data.
  *
  * Our message structure consists of:
  *	message structure
@@ -341,15 +343,31 @@ gb_operation_message_alloc(struct greybus_host_device *hd, u8 type,
 	buffer = &message->buffer[0];
 	header = (struct gb_operation_msg_hdr *)(buffer + hd->buffer_headroom);
 
-	/* Fill in the header structure */
-	header->size = cpu_to_le16(message_size);
-	header->operation_id = 0;	/* Filled in when submitted */
-	header->type = type;
-
 	message->header = header;
 	message->payload = header + 1;
 	message->size = message_size;
 
+	/*
+	 * The type supplied for incoming message buffers will be
+	 * 0x00.  Such buffers will be overwritten by arriving data
+	 * so there's no need to initialize the message header.
+	 */
+	if (type) {
+		/*
+		 * For a request, the operation id gets filled in
+		 * when the message is sent.  For a response, it
+		 * will be copied from the request by the caller.
+		 *
+		 * The result field in a request message must be
+		 * zero.  It will be set just prior to sending for
+		 * a response.
+		 */
+		header->size = cpu_to_le16(message_size);
+		header->operation_id = 0;
+		header->type = type;
+		header->result = 0;
+	}
+
 	return message;
 }
 
@@ -392,27 +410,32 @@ int gb_operation_status_map(u8 status)
 /*
  * Create a Greybus operation to be sent over the given connection.
  * The request buffer will be big enough for a payload of the given
- * size.  Outgoing requests must specify the size of the response
- * buffer size, which must be sufficient to hold all expected
- * response data.
+ * size.
+ *
+ * For outgoing requests, the request message's header will be
+ * initialized with the type of the request and the message size.
+ * Outgoing operations must also specify the response buffer size,
+ * which must be sufficient to hold all expected response data.  The
+ * response message header will eventually be overwritten, so there's
+ * no need to initialize it here.
  *
- * Incoming requests will supply a response size of 0, and in that
- * case no response buffer is allocated.  (A response always
- * includes a status byte, so 0 is not a valid size.)  Whatever
- * handles the operation request is responsible for allocating the
- * response buffer.
+ * Request messages for incoming operations can arrive in interrupt
+ * context, so they must be allocated with GFP_ATOMIC.  In this case
+ * the request buffer will be immediately overwritten, so there is
+ * no need to initialize the message header.  Responsibility for
+ * allocating a response buffer lies with the incoming request
+ * handler for a protocol.  So we don't allocate that here.
  *
  * Returns a pointer to the new operation or a null pointer if an
  * error occurs.
  */
 static struct gb_operation *
-gb_operation_create_common(struct gb_connection *connection, bool outgoing,
-				u8 type, size_t request_size,
-				size_t response_size)
+gb_operation_create_common(struct gb_connection *connection, u8 type,
+				size_t request_size, size_t response_size)
 {
 	struct greybus_host_device *hd = connection->hd;
 	struct gb_operation *operation;
-	gfp_t gfp_flags = outgoing ? GFP_KERNEL : GFP_ATOMIC;
+	gfp_t gfp_flags = type ? GFP_KERNEL : GFP_ATOMIC;
 
 	operation = kmem_cache_zalloc(gb_operation_cache, gfp_flags);
 	if (!operation)
@@ -425,7 +448,8 @@ gb_operation_create_common(struct gb_connection *connection, bool outgoing,
 		goto err_cache;
 	operation->request->operation = operation;
 
-	if (outgoing) {
+	/* Allocate the response buffer for outgoing operations */
+	if (type) {
 		type |= GB_OPERATION_TYPE_RESPONSE;
 		operation->response = gb_operation_message_alloc(hd, type,
 						response_size, GFP_KERNEL);
@@ -472,21 +496,19 @@ struct gb_operation *gb_operation_create(struct gb_connection *connection,
 	if (WARN_ON_ONCE(type & GB_OPERATION_TYPE_RESPONSE))
 		type &= ~GB_OPERATION_TYPE_RESPONSE;
 
-	return gb_operation_create_common(connection, true, type,
+	return gb_operation_create_common(connection, type,
 					request_size, response_size);
 }
 
 static struct gb_operation *
-gb_operation_create_incoming(struct gb_connection *connection,
-					u16 operation_id, u8 type,
+gb_operation_create_incoming(struct gb_connection *connection, u16 id,
 					void *data, size_t request_size)
 {
 	struct gb_operation *operation;
 
-	operation = gb_operation_create_common(connection, false, type,
-						request_size, 0);
+	operation = gb_operation_create_common(connection, 0, request_size, 0);
 	if (operation) {
-		operation->id = operation_id;
+		operation->id = id;
 		memcpy(operation->request->header, data, request_size);
 	}
 
@@ -638,13 +660,13 @@ EXPORT_SYMBOL_GPL(greybus_data_sent);
  * data into the request buffer and handle the rest via workqueue.
  */
 static void gb_connection_recv_request(struct gb_connection *connection,
-				       u16 operation_id, u8 type, void *data,
+				       u16 operation_id, void *data,
 				       size_t size)
 {
 	struct gb_operation *operation;
 
 	operation = gb_operation_create_incoming(connection, operation_id,
-						type, data, size);
+						data, size);
 	if (!operation) {
 		gb_connection_err(connection, "can't create operation");
 		return;		/* XXX Respond with pre-allocated ENOMEM */
@@ -732,7 +754,7 @@ void gb_connection_recv(struct gb_connection *connection,
 						header->result, data, msg_size);
 	else
 		gb_connection_recv_request(connection, operation_id,
-						header->type, data, msg_size);
+						data, msg_size);
 }
 
 /*