ALSA: usb-audio: fix delay account during pause

When a playback stream is paused, the stream isn't actually stopped,
thus we still need to take care of the in-flight data amount for the
delay calculation.  Otherwise the value of subs->last_delay is no
longer reliable and can give a bogus value after resuming from pause.
This will result in "delay: estimated XX, actual YY" error messages.

Also, during pause after all in flight data are processed
(i.e. last_delay = 0), we don't have to calculate the actual delay
from the current frame.  Give a short path in such a case.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 17 insertions, 1 deletions

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 8e1d5e00c182..7c64b9560b18 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -46,6 +46,9 @@ snd_pcm_uframes_t snd_usb_pcm_delay(struct snd_usb_substream *subs,
         int frame_diff;
         int est_delay;
 
+        if (!subs->last_delay)
+                return 0; /* short path */
+
         current_frame_number = usb_get_current_frame_number(subs->dev);
         /*
          * HCD implementations use different widths, use lower 8 bits.
@@ -1195,6 +1198,9 @@ static void retire_playback_urb(struct snd_usb_substream *subs,
                 return;
 
         spin_lock_irqsave(&subs->lock, flags);
+        if (!subs->last_delay)
+                goto out; /* short path */
+
         est_delay = snd_usb_pcm_delay(subs, runtime->rate);
         /* update delay with exact number of samples played */
         if (processed > subs->last_delay)
@@ -1212,6 +1218,15 @@ static void retire_playback_urb(struct snd_usb_substream *subs,
                 snd_printk(KERN_DEBUG "delay: estimated %d, actual %d\n",
                         est_delay, subs->last_delay);
 
+        if (!subs->running) {
+                /* update last_frame_number for delay counting here since
+                 * prepare_playback_urb won't be called during pause
+                 */
+                subs->last_frame_number =
+                        usb_get_current_frame_number(subs->dev) & 0xff;
+        }
+
+ out:
         spin_unlock_irqrestore(&subs->lock, flags);
 }
 
@@ -1253,7 +1268,8 @@ static int snd_usb_substream_playback_trigger(struct snd_pcm_substream *substrea
                 return 0;
         case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
                 subs->data_endpoint->prepare_data_urb = NULL;
-                subs->data_endpoint->retire_data_urb = NULL;
+                /* keep retire_data_urb for delay calculation */
+                subs->data_endpoint->retire_data_urb = retire_playback_urb;
                 subs->running = 0;
                 return 0;
         }