svn commit: r308437 - head/sys/dev/sound/usb

[Hans Petter Selasky]

Author: hselasky
Date: Tue Nov  8 08:09:48 2016
New Revision: 308437
URL: https://svnweb.freebsd.org/changeset/base/308437

Log:
  Range check the jitter values to avoid bogus sample rate adjustments.
  The expected deviation should not be more than 1Hz per second. The USB
  v2.0 specification also mandates this requirement. Refer to chapter
  5.12.4.2 about feedback.
  
  PR:		208791
  MFC after:	3 days

Modified:
  head/sys/dev/sound/usb/uaudio.c

Modified: head/sys/dev/sound/usb/uaudio.c
==============================================================================
--- head/sys/dev/sound/usb/uaudio.c	Tue Nov  8 07:18:39 2016	(r308436)
+++ head/sys/dev/sound/usb/uaudio.c	Tue Nov  8 08:09:48 2016	(r308437)
@@ -2078,9 +2078,22 @@ uaudio_chan_play_sync_callback(struct us
 		 * Use feedback value as fallback when there is no
 		 * recording channel:
 		 */
-		if (ch->priv_sc->sc_rec_chan.num_alt == 0)
-			ch->jitter_curr = temp - sample_rate;
-
+		if (ch->priv_sc->sc_rec_chan.num_alt == 0) {
+			/*
+			 * Range check the jitter values to avoid
+			 * bogus sample rate adjustments. The expected
+			 * deviation should not be more than 1Hz per
+			 * second. The USB v2.0 specification also
+			 * mandates this requirement. Refer to chapter
+			 * 5.12.4.2 about feedback.
+			 */
+			if (temp > sample_rate)
+				ch->jitter_curr = 1;
+			else if (temp < sample_rate)
+				ch->jitter_curr = -1;
+			else
+				ch->jitter_curr = 0;
+		}
 		ch->feedback_rate = temp;
 		break;