greybus: operation: add support for short responses

Add support for operations with short responses.

So far we have assumed that the initiator of an operation always knows
the exact size of the expected response. This is however not always the
case and we've worked around this limitation in a couple of places by,
for example, first requesting the size of a resource before fetching the
actual data.

To avoid such workarounds and simplify our protocols, add a
short-response flag that can be set when allocating an operation. When
this flag is set on an operation, core will accept a response that is
shorter than the size of the (pre-allocated) response payload buffer.

For now, we update the response-message payload_size field to reflect
the actual length of the response received.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

1 files changed, 25 insertions, 10 deletions

diff --git a/drivers/staging/greybus/operation.c b/drivers/staging/greybus/operation.c
index 9de548d1a05c..5818d7c92c4e 100644
--- a/drivers/staging/greybus/operation.c
+++ b/drivers/staging/greybus/operation.c
@@ -530,20 +530,25 @@ err_cache:
  * invalid operation type for all protocols, and this is enforced
  * here.
  */
-struct gb_operation *gb_operation_create(struct gb_connection *connection,
-					u8 type, size_t request_size,
-					size_t response_size,
-					gfp_t gfp)
+struct gb_operation *
+gb_operation_create_flags(struct gb_connection *connection,
+				u8 type, size_t request_size,
+				size_t response_size, unsigned long flags,
+				gfp_t gfp)
 {
 	if (WARN_ON_ONCE(type == GB_OPERATION_TYPE_INVALID))
 		return NULL;
 	if (WARN_ON_ONCE(type & GB_MESSAGE_TYPE_RESPONSE))
 		type &= ~GB_MESSAGE_TYPE_RESPONSE;
 
+	if (WARN_ON_ONCE(flags & ~GB_OPERATION_FLAG_USER_MASK))
+		flags &= GB_OPERATION_FLAG_USER_MASK;
+
 	return gb_operation_create_common(connection, type,
-					request_size, response_size, 0, gfp);
+						request_size, response_size,
+						flags, gfp);
 }
-EXPORT_SYMBOL_GPL(gb_operation_create);
+EXPORT_SYMBOL_GPL(gb_operation_create_flags);
 
 size_t gb_operation_get_payload_size_max(struct gb_connection *connection)
 {
@@ -875,12 +880,22 @@ static void gb_connection_recv_response(struct gb_connection *connection,
 	message = operation->response;
 	header = message->header;
 	message_size = sizeof(*header) + message->payload_size;
-	if (!errno && size != message_size) {
+	if (!errno && size > message_size) {
 		dev_err(&connection->hd->dev,
-			"%s: malformed response 0x%02x received (%zu != %zu)\n",
-			connection->name, header->type, size,
-			message_size);
+				"%s: malformed response 0x%02x received (%zu > %zu)\n",
+				connection->name, header->type,
+				size, message_size);
 		errno = -EMSGSIZE;
+	} else if (!errno && size < message_size) {
+		if (gb_operation_short_response_allowed(operation)) {
+			message->payload_size = size - sizeof(*header);
+		} else {
+			dev_err(&connection->hd->dev,
+					"%s: short response 0x%02x received (%zu < %zu)\n",
+					connection->name, header->type,
+					size, message_size);
+			errno = -EMSGSIZE;
+		}
 	}
 	trace_gb_message_recv_response(operation->response);