greybus: core: add lower-limit for host-device buffers

Make sure we never end up with a host device with maximum buffer size
smaller than the shortest Greybus message.
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/core.c

@@ -188,6 +188,11 @@ struct greybus_host_device *greybus_create_hd(struct greybus_host_driver *driver
 		return NULL;
 	}
 
+	if (buffer_size_max < GB_OPERATION_MESSAGE_SIZE_MIN) {
+		dev_err(parent, "greybus host-device buffers too small\n");
+		return NULL;
+	}
+
 	/*
 	 * Make sure to never allocate messages larger than what the Greybus
 	 * protocol supports.

drivers/staging/greybus/operation.h

@@ -69,6 +69,7 @@ struct gb_operation_msg_hdr {
 	__u8	pad[2];		/* must be zero (ignore when read) */
 } __aligned(sizeof(u64));
 
+#define GB_OPERATION_MESSAGE_SIZE_MIN	sizeof(struct gb_operation_msg_hdr)
 #define GB_OPERATION_MESSAGE_SIZE_MAX	U16_MAX
 
 /*