diff --git a/protocol.c b/protocol.c
index 2a04d89..76bc6ea 100644
--- a/protocol.c
+++ b/protocol.c
@@ -7,8 +7,9 @@
 
 #include "common.h"
 #include "flash.h"
-#include "mboxd.h"
 #include "lpc.h"
+#include "mboxd.h"
+#include "protocol.h"
 #include "windows.h"
 
 #define BLOCK_SIZE_SHIFT_V1		12 /* 4K */
@@ -76,15 +77,18 @@
 	return context->transport->clear_events(context, bmc_event, mask);
 }
 
-int protocol_v1_reset(struct mbox_context *context)
+static int protocol_v1_reset(struct mbox_context *context)
 {
 	/* Host requested it -> No BMC Event */
 	windows_reset_all(context);
 	return lpc_reset(context);
 }
 
-int protocol_v1_get_info(struct mbox_context *context,
-			 struct protocol_get_info *io)
+static int protocol_negotiate_version(struct mbox_context *context,
+				      uint8_t requested);
+
+static int protocol_v1_get_info(struct mbox_context *context,
+				struct protocol_get_info *io)
 {
 	uint8_t old_version = context->version;
 	int rc;
@@ -120,7 +124,7 @@
 	return lpc_map_memory(context);
 }
 
-int protocol_v1_get_flash_info(struct mbox_context *context,
+static int protocol_v1_get_flash_info(struct mbox_context *context,
 			       struct protocol_get_flash_info *io)
 {
 	io->resp.v1.flash_size = context->flash_size;
@@ -149,11 +153,18 @@
 	return lpc_addr >> context->block_size_shift;
 }
 
-int protocol_v1_create_window(struct mbox_context *context,
-			      struct protocol_create_window *io)
+static int protocol_v1_create_window(struct mbox_context *context,
+				     struct protocol_create_window *io)
 {
-	int rc;
 	uint32_t offset = io->req.offset << context->block_size_shift;
+	uint32_t size = io->req.size << context->block_size_shift;
+	int rc;
+
+	rc = flash_validate(context, offset, size, io->req.ro);
+	if (rc < 0) {
+		/* Backend does not allow window to be created. */
+		return rc;
+	}
 
 	/* Close the current window if there is one */
 	if (context->current) {
@@ -202,8 +213,8 @@
 	return 0;
 }
 
-int protocol_v1_mark_dirty(struct mbox_context *context,
-			   struct protocol_mark_dirty *io)
+static int protocol_v1_mark_dirty(struct mbox_context *context,
+				  struct protocol_mark_dirty *io)
 {
 	uint32_t offset = io->req.v1.offset;
 	uint32_t size = io->req.v1.size;
@@ -305,7 +316,8 @@
 				  WINDOW_CLEAN);
 }
 
-int protocol_v1_flush(struct mbox_context *context, struct protocol_flush *io)
+static int protocol_v1_flush(struct mbox_context *context,
+			     struct protocol_flush *io)
 {
 	int rc;
 
@@ -331,7 +343,8 @@
 	return generic_flush(context);
 }
 
-int protocol_v1_close(struct mbox_context *context, struct protocol_close *io)
+static int protocol_v1_close(struct mbox_context *context,
+			     struct protocol_close *io)
 {
 	int rc;
 
@@ -355,7 +368,8 @@
 	return 0;
 }
 
-int protocol_v1_ack(struct mbox_context *context, struct protocol_ack *io)
+static int protocol_v1_ack(struct mbox_context *context,
+			   struct protocol_ack *io)
 {
 	return protocol_events_clear(context,
 				     (io->req.flags & BMC_EVENT_ACK_MASK));
@@ -380,8 +394,8 @@
 	return ret;
 }
 
-int protocol_v2_get_info(struct mbox_context *context,
-			 struct protocol_get_info *io)
+static int protocol_v2_get_info(struct mbox_context *context,
+				struct protocol_get_info *io)
 {
 	uint8_t old_version = context->version;
 	int rc;
@@ -415,8 +429,8 @@
 	return lpc_map_memory(context);
 }
 
-int protocol_v2_get_flash_info(struct mbox_context *context,
-			       struct protocol_get_flash_info *io)
+static int protocol_v2_get_flash_info(struct mbox_context *context,
+				      struct protocol_get_flash_info *io)
 {
 	io->resp.v2.flash_size =
 		context->flash_size >> context->block_size_shift;
@@ -426,8 +440,8 @@
 	return 0;
 }
 
-int protocol_v2_create_window(struct mbox_context *context,
-			      struct protocol_create_window *io)
+static int protocol_v2_create_window(struct mbox_context *context,
+				     struct protocol_create_window *io)
 {
 	int rc;
 
@@ -442,8 +456,8 @@
 	return 0;
 }
 
-int protocol_v2_mark_dirty(struct mbox_context *context,
-			   struct protocol_mark_dirty *io)
+static int protocol_v2_mark_dirty(struct mbox_context *context,
+				  struct protocol_mark_dirty *io)
 {
 	if (!(context->current && context->current_is_write)) {
 		MSG_ERR("Tried to call mark dirty without open write window\n");
@@ -458,8 +472,8 @@
 				  io->req.v2.size, WINDOW_DIRTY);
 }
 
-int protocol_v2_erase(struct mbox_context *context,
-		      struct protocol_erase *io)
+static int protocol_v2_erase(struct mbox_context *context,
+			     struct protocol_erase *io)
 {
 	size_t start, len;
 	int rc;
@@ -487,7 +501,8 @@
 	return 0;
 }
 
-int protocol_v2_flush(struct mbox_context *context, struct protocol_flush *io)
+static int protocol_v2_flush(struct mbox_context *context,
+			     struct protocol_flush *io)
 {
 	if (!(context->current && context->current_is_write)) {
 		MSG_ERR("Tried to call flush without open write window\n");
@@ -497,7 +512,8 @@
 	return generic_flush(context);
 }
 
-int protocol_v2_close(struct mbox_context *context, struct protocol_close *io)
+static int protocol_v2_close(struct mbox_context *context,
+			     struct protocol_close *io)
 {
 	int rc;
 
@@ -521,6 +537,51 @@
 	return 0;
 }
 
+static const struct protocol_ops protocol_ops_v1 = {
+	.reset = protocol_v1_reset,
+	.get_info = protocol_v1_get_info,
+	.get_flash_info = protocol_v1_get_flash_info,
+	.create_window = protocol_v1_create_window,
+	.mark_dirty = protocol_v1_mark_dirty,
+	.erase = NULL,
+	.flush = protocol_v1_flush,
+	.close = protocol_v1_close,
+	.ack = protocol_v1_ack,
+};
+
+static const struct protocol_ops protocol_ops_v2 = {
+	.reset = protocol_v1_reset,
+	.get_info = protocol_v2_get_info,
+	.get_flash_info = protocol_v2_get_flash_info,
+	.create_window = protocol_v2_create_window,
+	.mark_dirty = protocol_v2_mark_dirty,
+	.erase = protocol_v2_erase,
+	.flush = protocol_v2_flush,
+	.close = protocol_v2_close,
+	.ack = protocol_v1_ack,
+};
+
+static const struct protocol_ops *protocol_ops_map[] = {
+	[0] = NULL,
+	[1] = &protocol_ops_v1,
+	[2] = &protocol_ops_v2,
+};
+
+static int protocol_negotiate_version(struct mbox_context *context,
+				      uint8_t requested)
+{
+	/* Check we support the version requested */
+	if (requested < API_MIN_VERSION)
+		return -EINVAL;
+
+	context->version = (requested > API_MAX_VERSION) ?
+				API_MAX_VERSION : requested;
+
+	context->protocol = protocol_ops_map[context->version];
+
+	return context->version;
+}
+
 int protocol_init(struct mbox_context *context)
 {
 	protocol_negotiate_version(context, API_MAX_VERSION);