firewire: core: detect device quirk when reading configuration ROM

Every time the bus manager runs, the cached configuration ROM content of
the IRM device is investigated to detect device-specific quirks. This
detection can be performed in advance when reading the configuration ROM.

This commit adds device quirk flags to the fw_device structure, and
initializes them after reading the bus information block of the
configuration ROM. The quirk flags are immutable once the configuration
ROM has been read. Although they are likely accessed concurrently only by
the bus manager, this commit ensures safe access by preventing torn writes
and reads using the WRITE_ONCE()/READ_ONCE() macros.

Link: https://lore.kernel.org/r/20251013140311.97159-2-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

Author: takaswie

drivers/firewire/core-card.c

@@ -86,8 +86,6 @@ static size_t config_rom_length = 1 + 4 + 1 + 1;
  */
 #define DEFAULT_SPLIT_TIMEOUT	(2 * 8000)
 
-#define CANON_OUI		0x000085
-
 static void generate_config_rom(struct fw_card *card, __be32 *config_rom)
 {
 	struct fw_descriptor *desc;
@@ -308,11 +306,9 @@ __must_hold(&card->lock)
 		cpu_to_be32(local_id),
 	};
 	bool grace = time_is_before_jiffies64(card->reset_jiffies + msecs_to_jiffies(125));
-	bool irm_is_1394_1995_only = false;
-	bool keep_this_irm = false;
 	struct fw_node *irm_node;
 	struct fw_device *irm_device;
-	int irm_node_id;
+	int irm_node_id, irm_device_quirks = 0;
 	int rcode;
 
 	lockdep_assert_held(&card->lock);
@@ -328,15 +324,12 @@ __must_hold(&card->lock)
 		return BM_CONTENTION_OUTCOME_IRM_HAS_LINK_OFF;
 	}
 
+	// NOTE: It is likely that the quirk detection for IRM device has not done yet.
 	irm_device = fw_node_get_device(irm_node);
-	if (irm_device && irm_device->config_rom) {
-		irm_is_1394_1995_only = (irm_device->config_rom[2] & 0x000000f0) == 0;
-
-		// Canon MV5i works unreliably if it is not root node.
-		keep_this_irm = irm_device->config_rom[3] >> 8 == CANON_OUI;
-	}
-
-	if (irm_is_1394_1995_only && !keep_this_irm) {
+	if (irm_device)
+		irm_device_quirks = READ_ONCE(irm_device->quirks);
+	if ((irm_device_quirks & FW_DEVICE_QUIRK_IRM_IS_1394_1995_ONLY) &&
+	    !(irm_device_quirks & FW_DEVICE_QUIRK_IRM_IGNORES_BUS_MANAGER)) {
 		fw_notice(card, "IRM is not 1394a compliant, making local node (%02x) root\n",
 			  local_id);
 		return BM_CONTENTION_OUTCOME_IRM_COMPLIES_1394_1995_ONLY;
@@ -373,7 +366,7 @@ __must_hold(&card->lock)
 			return BM_CONTENTION_OUTCOME_IRM_HOLDS_LOCAL_NODE_AS_BM;
 	}
 	default:
-		if (!keep_this_irm) {
+		if (!(irm_device_quirks & FW_DEVICE_QUIRK_IRM_IGNORES_BUS_MANAGER)) {
 			fw_notice(card, "BM lock failed (%s), making local node (%02x) root\n",
 				  fw_rcode_string(rcode), local_id);
 			return BM_CONTENTION_OUTCOME_IRM_COMPLIES_1394_1995_ONLY;

drivers/firewire/core-device.c

@@ -542,6 +542,21 @@ static struct device_attribute fw_device_attributes[] = {
 	__ATTR_NULL,
 };
 
+#define CANON_OUI		0x000085
+
+static int detect_quirks_by_bus_information_block(const u32 *bus_information_block)
+{
+	int quirks = 0;
+
+	if ((bus_information_block[2] & 0x000000f0) == 0)
+		quirks |= FW_DEVICE_QUIRK_IRM_IS_1394_1995_ONLY;
+
+	if ((bus_information_block[3] >> 8) == CANON_OUI)
+		quirks |= FW_DEVICE_QUIRK_IRM_IGNORES_BUS_MANAGER;
+
+	return quirks;
+}
+
 static int read_rom(struct fw_device *device,
 		    int generation, int index, u32 *data)
 {
@@ -582,6 +597,7 @@ static int read_config_rom(struct fw_device *device, int generation)
 	u32 *rom, *stack;
 	u32 sp, key;
 	int i, end, length, ret;
+	int quirks;
 
 	rom = kmalloc(sizeof(*rom) * MAX_CONFIG_ROM_SIZE +
 		      sizeof(*stack) * MAX_CONFIG_ROM_SIZE, GFP_KERNEL);
@@ -612,6 +628,11 @@ static int read_config_rom(struct fw_device *device, int generation)
 		}
 	}
 
+	quirks = detect_quirks_by_bus_information_block(rom);
+
+	// Just prevent from torn writing/reading.
+	WRITE_ONCE(device->quirks, quirks);
+
 	device->max_speed = device->node->max_speed;
 
 	/*
@@ -1122,10 +1143,10 @@ static void fw_device_init(struct work_struct *work)
 		device->workfn = fw_device_shutdown;
 		fw_schedule_device_work(device, SHUTDOWN_DELAY);
 	} else {
-		fw_notice(card, "created device %s: GUID %08x%08x, S%d00\n",
+		fw_notice(card, "created device %s: GUID %08x%08x, S%d00, quirks %08x\n",
 			  dev_name(&device->device),
 			  device->config_rom[3], device->config_rom[4],
-			  1 << device->max_speed);
+			  1 << device->max_speed, device->quirks);
 		device->config_rom_retries = 0;
 
 		set_broadcast_channel(device, device->generation);

include/linux/firewire.h

@@ -170,6 +170,14 @@ struct fw_attribute_group {
 	struct attribute *attrs[13];
 };
 
+enum fw_device_quirk {
+	// See afa1282a35d3 ("firewire: core: check for 1394a compliant IRM, fix inaccessibility of Sony camcorder").
+	FW_DEVICE_QUIRK_IRM_IS_1394_1995_ONLY = BIT(0),
+
+	// See a509e43ff338 ("firewire: core: fix unstable I/O with Canon camcorder").
+	FW_DEVICE_QUIRK_IRM_IGNORES_BUS_MANAGER = BIT(1),
+};
+
 enum fw_device_state {
 	FW_DEVICE_INITIALIZING,
 	FW_DEVICE_RUNNING,
@@ -203,6 +211,9 @@ struct fw_device {
 	struct fw_card *card;
 	struct device device;
 
+	// A set of enum fw_device_quirk.
+	int quirks;
+
 	struct mutex client_list_mutex;
 	struct list_head client_list;