[PATCH 2/3 v2] ALSA: usb-audio: avoid setting of sample rate multiple times on bus

[Jiada Wang <jiada_wang@mentor.com>]

From: Daniel Girnus <dgirnus@de.adit-jv.com>

ALSA usually calls the prepare function twice before starting the playback:
1. On hw_params call from userland and
2. internally when starting the stream.
Some device are not able to manage this and they will stop playback
if the sample rate will be configured several times over USB protocol.

Signed-off-by: Jens Lorenz <jlorenz@de.adit-jv.com>
Signed-off-by: Jiada Wang <jiada_wang@mentor.com>
---
 sound/usb/pcm.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 44d178e..a522c9a 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -806,17 +806,18 @@ static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream)
 	if (ret < 0)
 		goto unlock;
 
-	iface = usb_ifnum_to_if(subs->dev, subs->cur_audiofmt->iface);
-	alts = &iface->altsetting[subs->cur_audiofmt->altset_idx];
-	ret = snd_usb_init_sample_rate(subs->stream->chip,
-				       subs->cur_audiofmt->iface,
-				       alts,
-				       subs->cur_audiofmt,
-				       subs->cur_rate);
-	if (ret < 0)
-		goto unlock;
-
 	if (subs->need_setup_ep) {
+
+		iface = usb_ifnum_to_if(subs->dev, subs->cur_audiofmt->iface);
+		alts = &iface->altsetting[subs->cur_audiofmt->altset_idx];
+		ret = snd_usb_init_sample_rate(subs->stream->chip,
+					       subs->cur_audiofmt->iface,
+					       alts,
+					       subs->cur_audiofmt,
+					       subs->cur_rate);
+		if (ret < 0)
+			goto unlock;
+
 		ret = configure_endpoint(subs);
 		if (ret < 0)
 			goto unlock;
-- 
2.9.3