ALSA: firewire-lib: drop initial NODATA or empty packet

The devices based on BeBoB ASICs or the devices in Tascam FireWire
series transfer a batch of NODATA packet or empty packet in the beginning
of packet streaming. To avoid processing them, current implementation uses
an option to skip processing content of tx packet during some initial
cycles. However, the hard-coded number is not enough useful.

This commit drops content of packets till the packet includes any event
firstly. The function of option is to skip processing content of tx packet
with any event after dropping.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20210524031346.50539-2-o-takashi@sakamocchi.jpSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/firewire/amdtp-stream.c

@@ -49,8 +49,10 @@
 #define CIP_FMT_MASK		0x3f000000
 #define CIP_FDF_MASK		0x00ff0000
 #define CIP_FDF_SHIFT		16
+#define CIP_FDF_NO_DATA		0xff
 #define CIP_SYT_MASK		0x0000ffff
 #define CIP_SYT_NO_INFO		0xffff
+#define CIP_NO_DATA		((CIP_FDF_NO_DATA << CIP_FDF_SHIFT) | CIP_SYT_NO_INFO)
 
 #define CIP_HEADER_SIZE		(sizeof(__be32) * CIP_HEADER_QUADLETS)
 
@@ -1198,6 +1200,99 @@ static void process_tx_packets_intermediately(struct fw_iso_context *context, u3
 	}
 }
 
+static void drop_tx_packets_initially(struct fw_iso_context *context, u32 tstamp,
+				      size_t header_length, void *header, void *private_data)
+{
+	struct amdtp_stream *s = private_data;
+	struct amdtp_domain *d = s->domain;
+	__be32 *ctx_header;
+	unsigned int count;
+	unsigned int events;
+	int i;
+
+	if (s->packet_index < 0)
+		return;
+
+	count = header_length / s->ctx_data.tx.ctx_header_size;
+
+	// Attempt to detect any event in the batch of packets.
+	events = 0;
+	ctx_header = header;
+	for (i = 0; i < count; ++i) {
+		unsigned int payload_quads =
+			(be32_to_cpu(*ctx_header) >> ISO_DATA_LENGTH_SHIFT) / sizeof(__be32);
+		unsigned int data_blocks;
+
+		if (s->flags & CIP_NO_HEADER) {
+			data_blocks = payload_quads / s->data_block_quadlets;
+		} else {
+			__be32 *cip_headers = ctx_header + IR_CTX_HEADER_DEFAULT_QUADLETS;
+
+			if (payload_quads < CIP_HEADER_QUADLETS) {
+				data_blocks = 0;
+			} else {
+				payload_quads -= CIP_HEADER_QUADLETS;
+
+				if (s->flags & CIP_UNAWARE_SYT) {
+					data_blocks = payload_quads / s->data_block_quadlets;
+				} else {
+					u32 cip1 = be32_to_cpu(cip_headers[1]);
+
+					// NODATA packet can includes any data blocks but they are
+					// not available as event.
+					if ((cip1 & CIP_NO_DATA) == CIP_NO_DATA)
+						data_blocks = 0;
+					else
+						data_blocks = payload_quads / s->data_block_quadlets;
+				}
+			}
+		}
+
+		events += data_blocks;
+
+		ctx_header += s->ctx_data.tx.ctx_header_size / sizeof(__be32);
+	}
+
+	drop_tx_packets(context, tstamp, header_length, header, s);
+
+	if (events > 0)
+		s->ctx_data.tx.event_starts = true;
+
+	// Decide the cycle count to begin processing content of packet in IR contexts.
+	{
+		unsigned int stream_count = 0;
+		unsigned int event_starts_count = 0;
+		unsigned int cycle = UINT_MAX;
+
+		list_for_each_entry(s, &d->streams, list) {
+			if (s->direction == AMDTP_IN_STREAM) {
+				++stream_count;
+				if (s->ctx_data.tx.event_starts)
+					++event_starts_count;
+			}
+		}
+
+		if (stream_count == event_starts_count) {
+			unsigned int next_cycle;
+
+			list_for_each_entry(s, &d->streams, list) {
+				if (s->direction != AMDTP_IN_STREAM)
+					continue;
+
+				next_cycle = increment_ohci_cycle_count(s->next_cycle,
+								d->processing_cycle.tx_init_skip);
+				if (cycle == UINT_MAX ||
+				    compare_ohci_cycle_count(next_cycle, cycle) > 0)
+					cycle = next_cycle;
+
+				s->context->callback.sc = process_tx_packets_intermediately;
+			}
+
+			d->processing_cycle.tx_start = cycle;
+		}
+	}
+}
+
 static void process_ctxs_in_domain(struct amdtp_domain *d)
 {
 	struct amdtp_stream *s;
@@ -1277,20 +1372,14 @@ static void amdtp_stream_first_callback(struct fw_iso_context *context,
 {
 	struct amdtp_stream *s = private_data;
 	struct amdtp_domain *d = s->domain;
-	const __be32 *ctx_header = header;
-	u32 cycle;
 
 	// For in-stream, first packet has come.
 	// For out-stream, prepared to transmit first packet
 	s->callbacked = true;
 
 	if (s->direction == AMDTP_IN_STREAM) {
-		cycle = compute_ohci_cycle_count(ctx_header[1]);
-
-		context->callback.sc = drop_tx_packets;
+		context->callback.sc = drop_tx_packets_initially;
 	} else {
-		cycle = compute_ohci_it_cycle(*ctx_header, s->queue_size);
-
 		if (s == d->irq_target)
 			context->callback.sc = irq_target_callback_skip;
 		else
@@ -1298,38 +1387,6 @@ static void amdtp_stream_first_callback(struct fw_iso_context *context,
 	}
 
 	context->callback.sc(context, tstamp, header_length, header, s);
-
-	// Decide the cycle count to begin processing content of packet in IR contexts.
-	if (s->direction == AMDTP_IN_STREAM) {
-		unsigned int stream_count = 0;
-		unsigned int callbacked_count = 0;
-
-		list_for_each_entry(s, &d->streams, list) {
-			if (s->direction == AMDTP_IN_STREAM) {
-				++stream_count;
-				if (s->callbacked)
-					++callbacked_count;
-			}
-		}
-
-		if (stream_count == callbacked_count) {
-			unsigned int next_cycle;
-
-			list_for_each_entry(s, &d->streams, list) {
-				if (s->direction != AMDTP_IN_STREAM)
-					continue;
-
-				next_cycle = increment_ohci_cycle_count(s->next_cycle,
-								d->processing_cycle.tx_init_skip);
-				if (compare_ohci_cycle_count(next_cycle, cycle) > 0)
-					cycle = next_cycle;
-
-				s->context->callback.sc = process_tx_packets_intermediately;
-			}
-
-			d->processing_cycle.tx_start = cycle;
-		}
-	}
 }
 
 /**
@@ -1409,6 +1466,7 @@ static int amdtp_stream_start(struct amdtp_stream *s, int channel, int speed,
 	if (s->direction == AMDTP_IN_STREAM) {
 		s->ctx_data.tx.max_ctx_payload_length = max_ctx_payload_size;
 		s->ctx_data.tx.ctx_header_size = ctx_header_size;
+		s->ctx_data.tx.event_starts = false;
 	} else {
 		static const struct {
 			unsigned int data_block;

sound/firewire/amdtp-stream.h

@@ -138,6 +138,9 @@ struct amdtp_stream {
 			// Fixed interval of dbc between previos/current
 			// packets.
 			unsigned int dbc_interval;
+
+			// The device starts multiplexing events to the packet.
+			bool event_starts;
 		} tx;
 		struct {
 			// To generate CIP header.