ALSA: usb-audio: more tolerant packetsize

since commit 57e6dae1087b ("ALSA: usb-audio: do not trust too-big
wMaxPacketSize values"), the expected packetsize is always limited
to nominal + 25%. It was discovered, that some devices (Android audio
accessory) have a much higher jitter in used packetsizes than 25%
which would result in BABBLE condition and dropping of packets.
A better solution is so assume the jitter to be the nominal packetsize:
-one nearly empty packet followed by a almost 150% sized one.

V2: changed to assume max frequency is +50 of nominal packetsize.

Signed-off-by: Andreas Pape <apape@de.adit-jv.com>
Signed-off-by: Jiada Wang <jiada_wang@mentor.com>
Acked-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index c470251cea4b251269bcd3822f27d0e09e3cd1b2..a2931f49a1fca238b677b7061a878063107c1a78 100644 (file)
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -632,8 +632,8 @@ static int data_ep_set_params(struct snd_usb_endpoint *ep,
        ep->stride = frame_bits >> 3;
        ep->silence_value = pcm_format == SNDRV_PCM_FORMAT_U8 ? 0x80 : 0;
 
-       /* assume max. frequency is 25% higher than nominal */
-       ep->freqmax = ep->freqn + (ep->freqn >> 2);
+       /* assume max. frequency is 50% higher than nominal */
+       ep->freqmax = ep->freqn + (ep->freqn >> 1);
        /* Round up freqmax to nearest integer in order to calculate maximum
         * packet size, which must represent a whole number of frames.
         * This is accomplished by adding 0x0.ffff before converting the