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Re: [alsa-devel] [PATCH 1/3 v1] ALSA: usb-audio: more tolerant packetsize

From Takashi Iwai <tiwai@suse.de>
Newsgroups linux.kernel
Subject Re: [alsa-devel] [PATCH 1/3 v1] ALSA: usb-audio: more tolerant packetsize
Date 2016-12-01 10:10 +0100
Message-ID <sJvxo-1QI-43@gated-at.bofh.it> (permalink)
References <sJ7Y6-3eC-3@gated-at.bofh.it> <sJ7Y6-3eC-1@gated-at.bofh.it> <sJuhY-PI-25@gated-at.bofh.it>
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On Thu, 01 Dec 2016 08:41:17 +0100,
Clemens Ladisch wrote:
> 
> Jiada Wang wrote:
> > since commit 57e6dae1087bbaa6b33d3dd8a8e90b63888939a3 the expected packetsize is always limited to
> > nominal + 25%. It was discovered, that some devices
> 
> Which devices?
> 
> > have a much higher jitter in used packetsizes than 25%
> 
> How high?  (Please note that the USB specification restricts the jitter
> to at most one frame in consecutive packets.)
> 
> > which would result in BABBLE condition and dropping of packets.
> > A better solution is so assume the jitter to be the nominal packetsize
> 
> This solution is better for this one particular device, but how does it
> affect normal devices, or the Scarlett 2i4 on EHCI affected?

Actually, which value does this affected device in ep->maxpacksize?
In the commit mentioned above, we changed the logic to take +25%
frequency as the basis, and it my *reduce* if ep->maxpacksize is lower
than that.

OTOH, if ep->maxpacksize is sane, we can rely on it rather than the
implicit +25% frequency.  That said, maybe we can check
ep->maxpacksize whether it fits within the expected range, then adapt
it, or take +25% freq as fallback?


thanks,

Takashi

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[PATCH 1/3 v1] ALSA: usb-audio: more tolerant packetsize Jiada Wang <jiada_wang@mentor.com> - 2016-11-30 09:00 +0100
  Re: [PATCH 1/3 v1] ALSA: usb-audio: more tolerant packetsize Takashi Iwai <tiwai@suse.de> - 2016-11-30 10:00 +0100
    Re: [PATCH 1/3 v1] ALSA: usb-audio: more tolerant packetsize Jiada Wang <jiada_wang@mentor.com> - 2016-12-01 08:10 +0100
  Re: [alsa-devel] [PATCH 1/3 v1] ALSA: usb-audio: more tolerant  packetsize Clemens Ladisch <clemens@ladisch.de> - 2016-12-01 08:50 +0100
    Re: [alsa-devel] [PATCH 1/3 v1] ALSA: usb-audio: more tolerant packetsize Takashi Iwai <tiwai@suse.de> - 2016-12-01 10:10 +0100
      Re: [alsa-devel] [PATCH 1/3 v1] ALSA: usb-audio: more tolerant  packetsize Clemens Ladisch <clemens@ladisch.de> - 2016-12-01 12:20 +0100
        Re: [alsa-devel] [PATCH 1/3 v1] ALSA: usb-audio: more tolerant packetsize Takashi Iwai <tiwai@suse.de> - 2016-12-01 12:30 +0100
          Re: [alsa-devel] [PATCH 1/3 v1] ALSA: usb-audio: more tolerant  packetsize Clemens Ladisch <clemens@ladisch.de> - 2016-12-01 13:00 +0100
    Re: [alsa-devel] [PATCH 1/3 v1] ALSA: usb-audio: more tolerant  packetsize Clemens Ladisch <clemens@ladisch.de> - 2016-12-01 13:20 +0100

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