Commit fd1a5059 authored Dec 06, 2016 by Andreas Pape Committed by Takashi Iwai Dec 06, 2016

ALSA: usb-audio: more tolerant packetsize



since commit 57e6dae1 ("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>

parent 1e2e3fe4

sound/usb/endpoint.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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

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