From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754092Ab0EKQJn (ORCPT ); Tue, 11 May 2010 12:09:43 -0400 Received: from buzzloop.caiaq.de ([212.112.241.133]:49349 "EHLO buzzloop.caiaq.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752934Ab0EKQJm (ORCPT ); Tue, 11 May 2010 12:09:42 -0400 Date: Tue, 11 May 2010 18:09:23 +0200 From: Daniel Mack To: Alan Stern Cc: 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, pedrib@gmail.com, Andrew Morton , dwmw2@infradead.org Subject: Re: [alsa-devel] USB transfer_buffer allocations on 64bit systems Message-ID: <20100511160923.GZ30801@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 12:06:09PM -0400, Alan Stern wrote: > On Wed, 12 May 2010, FUJITA Tomonori wrote: > > > > > Can you tell me all the exact process of DMA that the usb core and the > > > > driver do? > > > > > > 1. The audio driver stores data in urb->transfer_buffer. > > > > How urb->transfer_buffer is allocated? > > By kmalloc(). Right, Daniel? Yes, and that's precisely the reason for the whole thread ;) [...] > > The driver does only DMA_TO_DEVICE? Or you see DMA problems only with > > DMA_TO_DEVICE? > > The particular test that Pedro is running uses audio output only -- > he's sending sound data to a speaker and it comes out noisy. > > But the audio data has to come from somewhere, and I don't remember > where. Pedro, does the noise occur only when you're playing sound that > comes from a different USB device? What happens if you play sounds > that are stored on your hard disk, like an MP3 file? AFAIK that was playback from a file, yes. It would be interesting to have some results for the other direction as well, that's true. Thanks, Daniel