ALSA: firewire-lib: code refactoring for syt computation

In current implementation for outgoing AMDTP packet, the value of syt
field in CIP header is computed when calculating syt offset. For
future extension, it's convenient to split the computation and
calculation.

This commit splits them.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20200508043635.349339-6-o-takashi@sakamocchi.jpSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/firewire/amdtp-stream.c

@@ -383,10 +383,9 @@ static unsigned int calculate_data_blocks(struct amdtp_stream *s,
 	return data_blocks;
 }
 
-static unsigned int calculate_syt(struct amdtp_stream *s,
-				  unsigned int cycle)
+static unsigned int calculate_syt_offset(struct amdtp_stream *s)
 {
-	unsigned int syt_offset, phase, index, syt;
+	unsigned int syt_offset, phase, index;
 
 	if (s->ctx_data.rx.last_syt_offset < TICKS_PER_CYCLE) {
 		if (!cip_sfc_is_base_44100(s->sfc))
@@ -416,15 +415,10 @@ static unsigned int calculate_syt(struct amdtp_stream *s,
 		syt_offset = s->ctx_data.rx.last_syt_offset - TICKS_PER_CYCLE;
 	s->ctx_data.rx.last_syt_offset = syt_offset;
 
-	if (syt_offset < TICKS_PER_CYCLE) {
-		syt_offset += s->ctx_data.rx.transfer_delay;
-		syt = (cycle + syt_offset / TICKS_PER_CYCLE) << 12;
-		syt += syt_offset % TICKS_PER_CYCLE;
+	if (syt_offset >= TICKS_PER_CYCLE)
+		syt_offset = CIP_SYT_NO_INFO;
 
-		return syt & CIP_SYT_MASK;
-	} else {
-		return CIP_SYT_NO_INFO;
-	}
+	return syt_offset;
 }
 
 static void update_pcm_pointers(struct amdtp_stream *s,
@@ -740,6 +734,17 @@ static int generate_device_pkt_descs(struct amdtp_stream *s,
 	return 0;
 }
 
+static unsigned int compute_syt(unsigned int syt_offset, unsigned int cycle,
+				unsigned int transfer_delay)
+{
+	unsigned int syt;
+
+	syt_offset += transfer_delay;
+	syt = ((cycle + syt_offset / TICKS_PER_CYCLE) << 12) |
+	      (syt_offset % TICKS_PER_CYCLE);
+	return syt & CIP_SYT_MASK;
+}
+
 static void generate_ideal_pkt_descs(struct amdtp_stream *s,
 				     struct pkt_desc *descs,
 				     const __be32 *ctx_header,
@@ -751,9 +756,16 @@ static void generate_ideal_pkt_descs(struct amdtp_stream *s,
 	for (i = 0; i < packets; ++i) {
 		struct pkt_desc *desc = descs + i;
 		unsigned int index = (s->packet_index + i) % s->queue_size;
+		unsigned int syt_offset;
 
 		desc->cycle = compute_it_cycle(*ctx_header, s->queue_size);
-		desc->syt = calculate_syt(s, desc->cycle);
+		syt_offset = calculate_syt_offset(s);
+		if (syt_offset != CIP_SYT_NO_INFO) {
+			desc->syt = compute_syt(syt_offset, desc->cycle,
+						s->ctx_data.rx.transfer_delay);
+		} else {
+			desc->syt = syt_offset;
+		}
 		desc->data_blocks = calculate_data_blocks(s, desc->syt);
 
 		if (s->flags & CIP_DBC_IS_END_EVENT)