diff --git a/drivers/firewire/core-card.c b/drivers/firewire/core-card.c
index 7083bcc..5045156 100644
--- a/drivers/firewire/core-card.c
+++ b/drivers/firewire/core-card.c
@@ -57,6 +57,8 @@
 static int descriptor_count;
 
 static __be32 tmp_config_rom[256];
+/* ROM header, bus info block, root dir header, capabilities = 7 quadlets */
+static size_t config_rom_length = 1 + 4 + 1 + 1;
 
 #define BIB_CRC(v)		((v) <<  0)
 #define BIB_CRC_LENGTH(v)	((v) << 16)
@@ -73,7 +75,7 @@
 #define BIB_CMC			((1) << 30)
 #define BIB_IMC			((1) << 31)
 
-static size_t generate_config_rom(struct fw_card *card, __be32 *config_rom)
+static void generate_config_rom(struct fw_card *card, __be32 *config_rom)
 {
 	struct fw_descriptor *desc;
 	int i, j, k, length;
@@ -130,23 +132,30 @@
 	for (i = 0; i < j; i += length + 1)
 		length = fw_compute_block_crc(config_rom + i);
 
-	return j;
+	WARN_ON(j != config_rom_length);
 }
 
 static void update_config_roms(void)
 {
 	struct fw_card *card;
-	size_t length;
 
 	list_for_each_entry (card, &card_list, link) {
-		length = generate_config_rom(card, tmp_config_rom);
-		card->driver->set_config_rom(card, tmp_config_rom, length);
+		generate_config_rom(card, tmp_config_rom);
+		card->driver->set_config_rom(card, tmp_config_rom,
+					     config_rom_length);
 	}
 }
 
+static size_t required_space(struct fw_descriptor *desc)
+{
+	/* descriptor + entry into root dir + optional immediate entry */
+	return desc->length + 1 + (desc->immediate > 0 ? 1 : 0);
+}
+
 int fw_core_add_descriptor(struct fw_descriptor *desc)
 {
 	size_t i;
+	int ret;
 
 	/*
 	 * Check descriptor is valid; the length of all blocks in the
@@ -162,15 +171,21 @@
 
 	mutex_lock(&card_mutex);
 
-	list_add_tail(&desc->link, &descriptor_list);
-	descriptor_count++;
-	if (desc->immediate > 0)
+	if (config_rom_length + required_space(desc) > 256) {
+		ret = -EBUSY;
+	} else {
+		list_add_tail(&desc->link, &descriptor_list);
+		config_rom_length += required_space(desc);
 		descriptor_count++;
-	update_config_roms();
+		if (desc->immediate > 0)
+			descriptor_count++;
+		update_config_roms();
+		ret = 0;
+	}
 
 	mutex_unlock(&card_mutex);
 
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL(fw_core_add_descriptor);
 
@@ -179,6 +194,7 @@
 	mutex_lock(&card_mutex);
 
 	list_del(&desc->link);
+	config_rom_length -= required_space(desc);
 	descriptor_count--;
 	if (desc->immediate > 0)
 		descriptor_count--;
@@ -428,7 +444,6 @@
 int fw_card_add(struct fw_card *card,
 		u32 max_receive, u32 link_speed, u64 guid)
 {
-	size_t length;
 	int ret;
 
 	card->max_receive = max_receive;
@@ -437,8 +452,8 @@
 
 	mutex_lock(&card_mutex);
 
-	length = generate_config_rom(card, tmp_config_rom);
-	ret = card->driver->enable(card, tmp_config_rom, length);
+	generate_config_rom(card, tmp_config_rom);
+	ret = card->driver->enable(card, tmp_config_rom, config_rom_length);
 	if (ret == 0)
 		list_add_tail(&card->link, &card_list);