On Tue, 06 Dec 2016 06:46:14 +0100,
Jiada Wang wrote:
>
> From: Andreas Pape <apape@xxxxxxxxxxxxxx>
>
> 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 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.
Clemens, are you OK with this change?
Takashi
>
> Signed-off-by: Andreas Pape <apape@xxxxxxxxxxxxxx>
> Signed-off-by: Jiada Wang <jiada_wang@xxxxxxxxxx>
> ---
> 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..a2931f4 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 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
> --
> 2.9.3
>
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