ALSA: usb-audio: avoid setting of sample rate multiple times on bus

Some of userland applications call 'snd_pcm_hw_params()' and
'snd_pcm_hw_prepare()' sequentially, which means 'snd_pcm_hw_prepare()'
is called twice and the second 'snd_pcm_hw_prepare()' is called in
'SNDRV_PCM_STATE_PREPARED' state.

Some devices are not able to manage this and they will stop playback
if the sample rate will be configured several times over USB protocol.

V2: updated Changelog

Signed-off-by: Daniel Girnus <dgirnus@de.adit-jv.com>
Signed-off-by: Jens Lorenz <jlorenz@de.adit-jv.com>
Signed-off-by: Jiada Wang <jiada_wang@mentor.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 11 insertions, 10 deletions

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 44d178ee9177..a522c9af1f34 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;