From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756505Ab0EKRKq (ORCPT ); Tue, 11 May 2010 13:10:46 -0400 Received: from buzzloop.caiaq.de ([212.112.241.133]:43324 "EHLO buzzloop.caiaq.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756250Ab0EKRKp (ORCPT ); Tue, 11 May 2010 13:10:45 -0400 Date: Tue, 11 May 2010 19:10:25 +0200 From: Daniel Mack To: Pedro Ribeiro Cc: Alan Stern , FUJITA Tomonori , gregkh@suse.de, konrad.wilk@oracle.com, tiwai@suse.de, USB list , clemens@ladisch.de, Kernel development list , chrisw@sous-sol.org, iommu@lists.linux-foundation.org, andi@firstfloor.org, Andrew Morton , dwmw2@infradead.org Subject: Re: [alsa-devel] USB transfer_buffer allocations on 64bit systems Message-ID: <20100511171025.GB30801@buzzloop.caiaq.de> References: <20100512003450P.fujita.tomonori@lab.ntt.co.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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