ALSA: usb: refine delay information with USB frame counter

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / sound / usb / urb.c

diff --git a/sound/usb/urb.c b/sound/usb/urb.c
index e184349aee83f1e5a790deb43238186dab2b3355..b4dcccc237dc9aae008e609548bd47c2c8b4b333 100644 (file)
--- a/sound/usb/urb.c
+++ b/sound/usb/urb.c
@@ -718,7 +718,16 @@ static int prepare_playback_urb(struct snd_usb_substream *subs,
        subs->hwptr_done += bytes;
        if (subs->hwptr_done >= runtime->buffer_size * stride)
                subs->hwptr_done -= runtime->buffer_size * stride;
+
+       /* update delay with exact number of samples queued */
+       runtime->delay = subs->last_delay;
        runtime->delay += frames;
+       subs->last_delay = runtime->delay;
+
+       /* realign last_frame_number */
+       subs->last_frame_number = usb_get_current_frame_number(subs->dev);
+       subs->last_frame_number &= 0xFF; /* keep 8 LSBs */
+
        spin_unlock_irqrestore(&subs->lock, flags);
        urb->transfer_buffer_length = bytes;
        if (period_elapsed)
@@ -737,12 +746,27 @@ static int retire_playback_urb(struct snd_usb_substream *subs,
        unsigned long flags;
        int stride = runtime->frame_bits >> 3;
        int processed = urb->transfer_buffer_length / stride;
+       int est_delay;
 
        spin_lock_irqsave(&subs->lock, flags);
-       if (processed > runtime->delay)
-               runtime->delay = 0;
+
+       est_delay = snd_usb_pcm_delay(subs, runtime->rate);
+       /* update delay with exact number of samples played */
+       if (processed > subs->last_delay)
+               subs->last_delay = 0;
        else
-               runtime->delay -= processed;
+               subs->last_delay -= processed;
+       runtime->delay = subs->last_delay;
+
+       /*
+        * Report when delay estimate is off by more than 2ms.
+        * The error should be lower than 2ms since the estimate relies
+        * on two reads of a counter updated every ms.
+        */
+       if (abs(est_delay - subs->last_delay) * 1000 > runtime->rate * 2)
+               snd_printk(KERN_DEBUG "delay: estimated %d, actual %d\n",
+                       est_delay, subs->last_delay);
+
        spin_unlock_irqrestore(&subs->lock, flags);
        return 0;
 }