ALSA: bebob: give up updating streams at bus reset handler

DM1000/DM1100/DM1500 chipsets transfer packets with discontinue value in
'dbc' field of CIP header. For ALSA bebob driver, this makes its bus-reset
handler meaningless, because the discontinuity is detected quite earlier
than executing the handler.

This commit gives up updating streams at the bus reset handler.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/firewire/bebob/bebob.c

@@ -300,6 +300,22 @@ error:
 	return err;
 }
 
+/*
+ * This driver doesn't update streams in bus reset handler.
+ *
+ * DM1000/ DM1100/DM1500 chipsets with BeBoB firmware transfer packets with
+ * discontinued counter at bus reset. This discontinuity is immediately
+ * detected in packet streaming layer, then it sets XRUN to PCM substream.
+ *
+ * ALSA PCM applications can know the XRUN by getting -EPIPE from PCM operation.
+ * Then, they can recover the PCM substream by executing ioctl(2) with
+ * SNDRV_PCM_IOCTL_PREPARE. 'struct snd_pcm_ops.prepare' is called and drivers
+ * restart packet streaming.
+ *
+ * The above processing may be executed before this bus-reset handler is
+ * executed. When this handler updates streams with current isochronous
+ * channels, the streams already have the current ones.
+ */
 static void
 bebob_update(struct fw_unit *unit)
 {
@@ -310,10 +326,6 @@ bebob_update(struct fw_unit *unit)
 
 	fcp_bus_reset(bebob->unit);
 
-	mutex_lock(&bebob->mutex);
-	snd_bebob_stream_update_duplex(bebob);
-	mutex_unlock(&bebob->mutex);
-
 	if (bebob->deferred_registration) {
 		if (snd_card_register(bebob->card) < 0) {
 			snd_bebob_stream_destroy_duplex(bebob);