[alsa-devel] [PATCH 3/3] ALSA: bebob: link the order of establishing connections and Syt-match clock mode

[Takashi Sakamoto]

Originally BeBeB ASICs and firmware supports clock mode to synchronizing
to syt field of received isoc packet. This mode is known as 'SYT Match'
slightly described in IEC 61883-6 (but no detail mechanisms). In this
mode, drivers can control sampling clock in device. Driver for Windows
and macOS uses this feature to perform synchronization for devices
on the same bus.

In this mode, a plug of Music subunit for synchronization is connected
to a plug of isoc unit for incoming packet streaming, then the order to
establish connections is INPUT_PLUG first, OUTPUT_PLUG second.

This commit implements the above.

Actually each device works with its own clock for sampling, therefore
the original design is hardly implemented to vendor's products.

Signed-off-by: Takashi Sakamoto <o-takashi at sakamocchi.jp>
---
 sound/firewire/bebob/bebob_stream.c | 51 +++++++++++++----------------
 1 file changed, 22 insertions(+), 29 deletions(-)

diff --git a/sound/firewire/bebob/bebob_stream.c b/sound/firewire/bebob/bebob_stream.c
index 895a113635af..bbae04793c50 100644
--- a/sound/firewire/bebob/bebob_stream.c
+++ b/sound/firewire/bebob/bebob_stream.c
@@ -398,23 +398,6 @@ check_connection_used_by_others(struct snd_bebob *bebob, struct amdtp_stream *s)
 	return err;
 }
 
-static int make_both_connections(struct snd_bebob *bebob)
-{
-	int err = 0;
-
-	err = cmp_connection_establish(&bebob->out_conn);
-	if (err < 0)
-		return err;
-
-	err = cmp_connection_establish(&bebob->in_conn);
-	if (err < 0) {
-		cmp_connection_break(&bebob->out_conn);
-		return err;
-	}
-
-	return 0;
-}
-
 static void break_both_connections(struct snd_bebob *bebob)
 {
 	cmp_connection_break(&bebob->in_conn);
@@ -427,8 +410,7 @@ static void break_both_connections(struct snd_bebob *bebob)
 		msleep(600);
 }
 
-static int
-start_stream(struct snd_bebob *bebob, struct amdtp_stream *stream)
+static int start_stream(struct snd_bebob *bebob, struct amdtp_stream *stream)
 {
 	struct cmp_connection *conn;
 	int err = 0;
@@ -438,18 +420,19 @@ start_stream(struct snd_bebob *bebob, struct amdtp_stream *stream)
 	else
 		conn = &bebob->out_conn;
 
-	/* channel mapping */
+	// channel mapping.
 	if (bebob->maudio_special_quirk == NULL) {
 		err = map_data_channels(bebob, stream);
 		if (err < 0)
-			goto end;
+			return err;
 	}
 
-	// start amdtp stream.
-	err = amdtp_domain_add_stream(&bebob->domain, stream,
-				      conn->resources.channel, conn->speed);
-end:
-	return err;
+	err = cmp_connection_establish(conn);
+	if (err < 0)
+		return err;
+
+	return amdtp_domain_add_stream(&bebob->domain, stream,
+				       conn->resources.channel, conn->speed);
 }
 
 static int init_stream(struct snd_bebob *bebob, struct amdtp_stream *stream)
@@ -638,6 +621,8 @@ int snd_bebob_stream_start_duplex(struct snd_bebob *bebob)
 	}
 
 	if (!amdtp_stream_running(&bebob->rx_stream)) {
+		enum snd_bebob_clock_type src;
+		struct amdtp_stream *master, *slave;
 		unsigned int curr_rate;
 		unsigned int ir_delay_cycle;
 
@@ -647,15 +632,23 @@ int snd_bebob_stream_start_duplex(struct snd_bebob *bebob)
 				return err;
 		}
 
-		err = make_both_connections(bebob);
+		err = snd_bebob_stream_get_clock_src(bebob, &src);
 		if (err < 0)
 			return err;
 
-		err = start_stream(bebob, &bebob->rx_stream);
+		if (src != SND_BEBOB_CLOCK_TYPE_SYT) {
+			master = &bebob->tx_stream;
+			slave = &bebob->rx_stream;
+		} else {
+			master = &bebob->rx_stream;
+			slave = &bebob->tx_stream;
+		}
+
+		err = start_stream(bebob, master);
 		if (err < 0)
 			goto error;
 
-		err = start_stream(bebob, &bebob->tx_stream);
+		err = start_stream(bebob, slave);
 		if (err < 0)
 			goto error;
 
-- 
2.20.1