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>

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 8e1d5e00c182a48f9c0d8d923eaa926ff07ac054..7c64b9560b18ce723080af04c314ad2efd8003a0 100644 (file)
--- 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;
        }