firewire: core: handle device quirk of MOTU Audio Express

A commit 3a93d08 ("ALSA: firewire-motu: add support for MOTU Audio
Express") describes a quirk of MOTU Audio Express. The device returns
acknowledge packet with 0x10 as the pending state of any types of
asynchronous request transaction. It is completely out of specification.

This commit implements handling for that device-specific quirk. The quirk
is detected after reading the root directory of configuration ROM. When
processing the acknowledge code in 1394 OHCI AT context event handler,
firewire-ohci module seeks the device instance of destination node by
traversing device hierarchy. If the device has the quirk, the acknowledge
code is replaced with the standard code.

The 1394 OHCI AT context events occur for outgoing asynchronous request
packets. The device traversal is safe since no new request initiators
exist after the fw_card_instance has been invalidated.

Link: https://lore.kernel.org/r/20251013140311.97159-3-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

Author: takaswie

drivers/firewire/core-device.c

@@ -557,6 +557,54 @@ static int detect_quirks_by_bus_information_block(const u32 *bus_information_blo
 	return quirks;
 }
 
+struct entry_match {
+	unsigned int index;
+	u32 value;
+};
+
+static const struct entry_match motu_audio_express_matches[] = {
+	{ 1, 0x030001f2 },
+	{ 3, 0xd1000002 },
+	{ 4, 0x8d000005 },
+	{ 6, 0x120001f2 },
+	{ 7, 0x13000033 },
+	{ 8, 0x17104800 },
+};
+
+static int detect_quirks_by_root_directory(const u32 *root_directory, unsigned int length)
+{
+	static const struct {
+		enum fw_device_quirk quirk;
+		const struct entry_match *matches;
+		unsigned int match_count;
+	} *entry, entries[] = {
+		{
+			.quirk = FW_DEVICE_QUIRK_ACK_PACKET_WITH_INVALID_PENDING_CODE,
+			.matches = motu_audio_express_matches,
+			.match_count = ARRAY_SIZE(motu_audio_express_matches),
+		},
+	};
+	int quirks = 0;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(entries); ++i) {
+		int j;
+
+		entry = entries + i;
+		for (j = 0; j < entry->match_count; ++j) {
+			unsigned int index = entry->matches[j].index;
+			unsigned int value = entry->matches[j].value;
+
+			if ((length < index) || (root_directory[index] != value))
+				break;
+		}
+		if (j == entry->match_count)
+			quirks |= entry->quirk;
+	}
+
+	return quirks;
+}
+
 static int read_rom(struct fw_device *device,
 		    int generation, int index, u32 *data)
 {
@@ -737,6 +785,11 @@ static int read_config_rom(struct fw_device *device, int generation)
 			length = i;
 	}
 
+	quirks |= detect_quirks_by_root_directory(rom + ROOT_DIR_OFFSET, length - ROOT_DIR_OFFSET);
+
+	// Just prevent from torn writing/reading.
+	WRITE_ONCE(device->quirks, quirks);
+
 	old_rom = device->config_rom;
 	new_rom = kmemdup(rom, length * 4, GFP_KERNEL);
 	if (new_rom == NULL) {

drivers/firewire/ohci.c

@@ -1319,6 +1319,14 @@ static void at_context_flush(struct at_context *ctx)
 	enable_work(&ctx->work);
 }
 
+static int find_fw_device(struct device *dev, const void *data)
+{
+	struct fw_device *device = fw_device(dev);
+	const u32 *params = data;
+
+	return (device->generation == params[0]) && (device->node_id == params[1]);
+}
+
 static int handle_at_packet(struct context *context,
 			    struct descriptor *d,
 			    struct descriptor *last)
@@ -1390,6 +1398,27 @@ static int handle_at_packet(struct context *context,
 		fallthrough;
 
 	default:
+		if (unlikely(evt == 0x10)) {
+			u32 params[2] = {
+				packet->generation,
+				async_header_get_destination(packet->header),
+			};
+			struct device *dev;
+
+			fw_card_get(&ohci->card);
+			dev = device_find_child(ohci->card.device, (const void *)params, find_fw_device);
+			fw_card_put(&ohci->card);
+			if (dev) {
+				struct fw_device *device = fw_device(dev);
+				int quirks = READ_ONCE(device->quirks);
+
+				put_device(dev);
+				if (quirks & FW_DEVICE_QUIRK_ACK_PACKET_WITH_INVALID_PENDING_CODE) {
+					packet->ack = ACK_PENDING;
+					break;
+				}
+			}
+		}
 		packet->ack = RCODE_SEND_ERROR;
 		break;
 	}

include/linux/firewire.h

@@ -176,6 +176,9 @@ enum fw_device_quirk {
 
 	// See a509e43ff338 ("firewire: core: fix unstable I/O with Canon camcorder").
 	FW_DEVICE_QUIRK_IRM_IGNORES_BUS_MANAGER = BIT(1),
+
+	// MOTU Audio Express transfers acknowledge packet with 0x10 for pending state.
+	FW_DEVICE_QUIRK_ACK_PACKET_WITH_INVALID_PENDING_CODE = BIT(2),
 };
 
 enum fw_device_state {