ALSA: firewire-tascam: reserve resources for transferred isochronous packets at S400

TASCAM FW-1884/FW-1804/FW-1082 have a quirk that they often freeze when
receiving isochronous packets at S400. This behaviour is suppressed by a
new quirk flag added in Linux FireWire core to restrict maximum speed.
Consequently both of the asynchronous transactions and isochronous
transmissions are done at S200. However, the device still transfers
isochronous packet at S400, and the way to indicate the transmission
speed is not cleared yet.

This commit correctly reserves isochronous resources for the transferred
packet stream at S400. As a beneficial side effect, the pair of
isochronous transmissions for FW-1884 fits within the bandwidth capacity
of the bus.

Link: https://lore.kernel.org/r/20251018035532.287124-5-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

Author: takaswie

sound/firewire/tascam/tascam-stream.c

@@ -282,20 +282,22 @@ static int keep_resources(struct snd_tscm *tscm, unsigned int rate,
 			  struct amdtp_stream *stream)
 {
 	struct fw_iso_resources *resources;
+	int speed;
 	int err;
 
-	if (stream == &tscm->tx_stream)
+	if (stream == &tscm->tx_stream) {
 		resources = &tscm->tx_resources;
-	else
+		speed = fw_parent_device(tscm->unit)->max_speed;
+	} else {
 		resources = &tscm->rx_resources;
+		speed = SCODE_400;
+	}
 
 	err = amdtp_tscm_set_parameters(stream, rate);
 	if (err < 0)
 		return err;
 
-	return fw_iso_resources_allocate(resources,
-				amdtp_stream_get_max_payload(stream),
-				fw_parent_device(tscm->unit)->max_speed);
+	return fw_iso_resources_allocate(resources, amdtp_stream_get_max_payload(stream), speed);
 }
 
 static int init_stream(struct snd_tscm *tscm, struct amdtp_stream *s)
@@ -455,7 +457,6 @@ int snd_tscm_stream_start_duplex(struct snd_tscm *tscm, unsigned int rate)
 	}
 
 	if (!amdtp_stream_running(&tscm->rx_stream)) {
-		int spd = fw_parent_device(tscm->unit)->max_speed;
 		unsigned int tx_init_skip_cycles;
 
 		err = set_stream_formats(tscm, rate);
@@ -466,13 +467,13 @@ int snd_tscm_stream_start_duplex(struct snd_tscm *tscm, unsigned int rate)
 		if (err < 0)
 			goto error;
 
-		err = amdtp_domain_add_stream(&tscm->domain, &tscm->rx_stream,
-					      tscm->rx_resources.channel, spd);
+		err = amdtp_domain_add_stream(&tscm->domain, &tscm->rx_stream, tscm->rx_resources.channel,
+					      fw_parent_device(tscm->unit)->max_speed);
 		if (err < 0)
 			goto error;
 
-		err = amdtp_domain_add_stream(&tscm->domain, &tscm->tx_stream,
-					      tscm->tx_resources.channel, spd);
+		err = amdtp_domain_add_stream(&tscm->domain, &tscm->tx_stream, tscm->tx_resources.channel,
+					      SCODE_400);
 		if (err < 0)
 			goto error;