linux-kernel - Re: [alsa-devel] USB transfer_buffer allocations on 64bit systems

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Date:	Tue, 11 May 2010 18:32:50 +0100
From:	Pedro Ribeiro <pedrib@...il.com>
To:	Daniel Mack <daniel@...aq.de>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	gregkh@...e.de, konrad.wilk@...cle.com, tiwai@...e.de,
	USB list <linux-usb@...r.kernel.org>, clemens@...isch.de,
	Kernel development list <linux-kernel@...r.kernel.org>,
	chrisw@...s-sol.org, iommu@...ts.linux-foundation.org,
	andi@...stfloor.org, Andrew Morton <akpm@...ux-foundation.org>,
	dwmw2@...radead.org
Subject: Re: [alsa-devel] USB transfer_buffer allocations on 64bit systems

On 11 May 2010 18:10, Daniel Mack <daniel@...aq.de> wrote:
> On Tue, May 11, 2010 at 05:48:11PM +0100, Pedro Ribeiro wrote:
>> I'm clueless about the whole underlying process but I don't think it
>> is related to playing a file from the disk or another USB device.
>>
>> I don't need to play any file for this interference to be heard - I
>> just need to "open" the device. By this I mean that if I create a JACK
>
> ... which will stream zeros. Sure, that should also trigger the bug
> then.
>
>> server or if I open the device using the ALSA backed in a program like
>> Mixxx I immediately start hearing the cracks and pops in the speaker.
>> But to answer your question, playing a file from the hard drive using
>> aplay I can also hear the interference - but only when the sound is
>> playing. As soon as the sound stops and the audio device is "closed",
>> no interference occurs.
>
> Yes, because the stream is stopped, pending URBs are unlinked etc.
> That's completely expected.
>
>> However, when using the JACK server, which probably opens and polls
>> the audio card constantly (its a low latency audio server) I don't
>> even need to be playing any sound for the interference to be constant.
>
> That shouldn't affect the driver itself but just put the ALSA core under
> pressure.
>
>> I can also see it since I have 4 output leds in the USB audio card and
>> even if I'm only using 2 channels, the 4 channel leds light up with
>> interference as the sound cracks and pops.
>
> No surprise here. The 4 channels are mux'ed in an interleaved fashion,
> so if the buffers contain rubbish, you will hear artefacts on all
> channels.
>
> Daniel
>
>

So what would be the testcase you would like me to try?

Pedro
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