From: Clemens Ladisch <clemens@ladisch.de>
To: Takashi Iwai <tiwai@suse.de>
Cc: Jiada Wang <jiada_wang@mentor.com>,
alsa-devel@alsa-project.org, apape@de.adit-jv.com,
linux-kernel@vger.kernel.org, Mark_Craske@mentor.com
Subject: Re: [alsa-devel] [PATCH 1/3 v1] ALSA: usb-audio: more tolerant packetsize
Date: Thu, 1 Dec 2016 12:16:47 +0100 [thread overview]
Message-ID: <76fa143e-7092-0bc9-7d55-6a5605d4704a@ladisch.de> (raw)
In-Reply-To: <s5hy40010w5.wl-tiwai@suse.de>
Takashi Iwai wrote:
> 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?
You are describing how the current code behaves. The +25% limit _is_
what the code takes as the expected range.
I'm wondering if that unknown device just declares a wrong interval value.
Regards,
Clemens
next prev parent reply other threads:[~2016-12-01 11:16 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-30 7:59 [PATCH 0/3 v1] usb-misc fix Jiada Wang
2016-11-30 7:59 ` [PATCH 1/3 v1] ALSA: usb-audio: more tolerant packetsize Jiada Wang
2016-11-30 8:54 ` Takashi Iwai
2016-12-01 7:04 ` Jiada Wang
2016-12-01 7:41 ` [alsa-devel] " Clemens Ladisch
2016-12-01 8:58 ` Takashi Iwai
2016-12-01 11:16 ` Clemens Ladisch [this message]
2016-12-01 11:23 ` Takashi Iwai
2016-12-01 11:50 ` Clemens Ladisch
[not found] ` <58400B3A.7080806@mentor.com>
2016-12-01 12:15 ` Clemens Ladisch
2016-11-30 7:59 ` [PATCH 2/3 v2] ALSA: usb-audio: avoid setting of sample rate multiple times on bus Jiada Wang
2016-11-30 8:51 ` Takashi Iwai
2016-12-01 7:07 ` Jiada Wang
2016-11-30 10:45 ` Takashi Sakamoto
2016-11-30 22:19 ` Takashi Sakamoto
2016-12-05 7:32 ` Jiada Wang
2016-12-05 9:58 ` Takashi Sakamoto
2016-11-30 7:59 ` [PATCH 3/3 v3] ALSA: usb-audio: fix race in snd_usb_endpoint_stop Jiada Wang
2016-11-30 9:00 ` Takashi Iwai
2016-12-05 10:10 ` Jiada Wang
2016-12-05 10:30 ` Takashi Iwai
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