Re: [PATCH v2 1/2] ALSA: usb-audio: more tolerant packetsize

From	Takashi Iwai <tiwai@suse.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 1/2] ALSA: usb-audio: more tolerant packetsize
Date	2016-12-06 08:20 +0100
Message-ID	<sLicG-7oX-13@gated-at.bofh.it> (permalink)
References	<sLgNz-6if-1@gated-at.bofh.it> <sLgNz-6if-3@gated-at.bofh.it>
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On Tue, 06 Dec 2016 06:46:14 +0100,
Jiada Wang wrote:
> 
> From: Andreas Pape <apape@de.adit-jv.com>
> 
> 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@de.adit-jv.com>
> Signed-off-by: Jiada Wang <jiada_wang@mentor.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..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
>

Thread

[PATCH v2 1/2] ALSA: usb-audio: more tolerant packetsize Jiada Wang <jiada_wang@mentor.com> - 2016-12-06 06:50 +0100
  Re: [PATCH v2 1/2] ALSA: usb-audio: more tolerant packetsize Takashi Iwai <tiwai@suse.de> - 2016-12-06 08:20 +0100
  Re: [alsa-devel] [PATCH v2 1/2] ALSA: usb-audio: more tolerant         packetsize Clemens Ladisch <clemens@ladisch.de> - 2016-12-06 13:20 +0100

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