linux-kernel - [PATCH 1/3 v1] ALSA: usb-audio: more tolerant packetsize

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Date:   Wed, 30 Nov 2016 16:59:21 +0900
From:   Jiada Wang <jiada_wang@...tor.com>
To:     <perex@...ex.cz>, <tiwai@...e.com>
CC:     <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        <Mark_Craske@...tor.com>, <apape@...adit-jv.com>
Subject: [PATCH 1/3 v1] ALSA: usb-audio: more tolerant packetsize

From: Andreas Pape <apape@...adit-jv.com>

since commit 57e6dae1087bbaa6b33d3dd8a8e90b63888939a3 the expected packetsize is always limited to
nominal + 25%. It was discovered, that some devices 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 double sized one.

Signed-off-by: Andreas Pape <apape@...adit-jv.com>
Signed-off-by: Jiada Wang <jiada_wang@...tor.com>
---
 sound/usb/endpoint.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index c470251..2f592dd 100644
--- 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 double than nominal */
+	ep->freqmax = ep->freqn * 2;
 	/* 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
-- 
2.9.3