Messages in this thread | | | Subject | Re: [alsa-devel] [PATCH 1/3 v1] ALSA: usb-audio: more tolerant packetsize | From | Clemens Ladisch <> | Date | Thu, 1 Dec 2016 12:50:39 +0100 |
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Takashi Iwai wrote: > Clemens Ladisch wrote: >> Takashi Iwai wrote: >>> [...] >>> 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? >> >> You are describing how the current code behaves. The +25% limit _is_ >> what the code takes as the expected range. > > Well, the question is what is the "sane" range. +25% doesn't fit for > some devices.
The USB audio specification _requires_ that there is as little jitter as possible.
It's no surprise that some device violates the specification. But we don't know what the actual error is; whether we could adjust the packet size for this particular device only, or increase the limit for all devices, or use a completely different workaround.
> If maxpacksize fits without +100% as this patch suggests, can we rely > on it instead?
The packet size affect the following computations, like the number of packets per URB. I don't know how bad the effects would be.
Regards, Clemens
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