ALSA: usb-audio: Avoid doubly initialization for implicit fb

The implicit feedback mode initializes both the main data stream and
the sync data stream.  When a sync stream was already opened, this
would result in the doubly initialization and might screw up things.

Add the check of already opened sync streams and skip the unnecessary
initialization.
Tested-by: Keith Milner <kamilner@superlative.org>
Tested-by: Dylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-14-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/pcm.c

@@ -601,8 +601,9 @@ static int set_sync_endpoint(struct snd_usb_substream *subs,
 
 	subs->data_endpoint->sync_master = subs->sync_endpoint;
 
-	if (subs->data_endpoint->iface != subs->sync_endpoint->iface ||
-	    subs->data_endpoint->altsetting != subs->sync_endpoint->altsetting) {
+	if (!subs->sync_endpoint->use_count &&
+	    (subs->data_endpoint->iface != subs->sync_endpoint->iface ||
+	     subs->data_endpoint->altsetting != subs->sync_endpoint->altsetting)) {
 		err = usb_set_interface(subs->dev,
 					subs->sync_endpoint->iface,
 					subs->sync_endpoint->altsetting);
@@ -625,6 +626,7 @@ static int set_format(struct snd_usb_substream *subs, struct audioformat *fmt)
 	struct usb_device *dev = subs->dev;
 	struct usb_host_interface *alts;
 	struct usb_interface *iface;
+	struct snd_usb_endpoint *ep;
 	int err;
 
 	iface = usb_ifnum_to_if(dev, fmt->iface);
@@ -637,6 +639,14 @@ static int set_format(struct snd_usb_substream *subs, struct audioformat *fmt)
 	if (fmt == subs->cur_audiofmt && !subs->need_setup_fmt)
 		return 0;
 
+	/* shared EP with implicit fb */
+	if (fmt->implicit_fb && !subs->need_setup_fmt) {
+		ep = snd_usb_get_endpoint(subs->stream->chip, fmt->endpoint,
+					  fmt->iface, fmt->altsetting);
+		if (ep && ep->use_count > 0)
+			goto add_data_ep;
+	}
+
 	/* close the old interface */
 	if (subs->interface >= 0 && (subs->interface != fmt->iface || subs->need_setup_fmt)) {
 		if (!subs->stream->chip->keep_iface) {
@@ -673,6 +683,9 @@ static int set_format(struct snd_usb_substream *subs, struct audioformat *fmt)
 		snd_usb_set_interface_quirk(dev);
 	}
 
+	subs->need_setup_ep = true;
+
+ add_data_ep:
 	subs->interface = fmt->iface;
 	subs->altset_idx = fmt->altset_idx;
 	subs->data_endpoint = snd_usb_add_endpoint(subs->stream->chip,
@@ -686,9 +699,11 @@ static int set_format(struct snd_usb_substream *subs, struct audioformat *fmt)
 	if (err < 0)
 		return err;
 
+	if (subs->need_setup_ep) {
 		err = snd_usb_init_pitch(subs->stream->chip, fmt->iface, alts, fmt);
 		if (err < 0)
 			return err;
+	}
 
 	subs->cur_audiofmt = fmt;
 
@@ -940,10 +955,6 @@ static int snd_usb_hw_params(struct snd_pcm_substream *substream,
 	if (ret < 0)
 		goto unlock;
 
-	subs->interface = fmt->iface;
-	subs->altset_idx = fmt->altset_idx;
-	subs->need_setup_ep = true;
-
  unlock:
 	snd_usb_unlock_shutdown(subs->stream->chip);
 	if (ret < 0)