From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750902AbWAJBme (ORCPT ); Mon, 9 Jan 2006 20:42:34 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750886AbWAJBme (ORCPT ); Mon, 9 Jan 2006 20:42:34 -0500 Received: from [81.2.110.250] ([81.2.110.250]:52618 "EHLO lxorguk.ukuu.org.uk") by vger.kernel.org with ESMTP id S1750862AbWAJBmd (ORCPT ); Mon, 9 Jan 2006 20:42:33 -0500 Subject: Re: [Alsa-devel] Re: [OT] ALSA userspace API complexity From: Alan Cox To: David Lang Cc: John Rigg , =?ISO-8859-1?Q?Ren=E9?= Rebe , Hannu Savolainen , Jaroslav Kysela , Takashi Iwai , linux-sound@vger.kernel.org, ALSA development , LKML In-Reply-To: References: <20050726150837.GT3160@stusta.de> <200601091405.23939.rene@exactcode.de> <200601091812.55943.rene@exactcode.de> <20060109232043.GA5013@localhost.localdomain> <20060110001617.GA5154@localhost.localdomain> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Tue, 10 Jan 2006 00:44:58 +0000 Message-Id: <1136853898.12802.21.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-2.fc4) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Llu, 2006-01-09 at 16:29 -0800, David Lang wrote: > I was under the (apparently mistaken) impression that you couldn't DMA > from userspace (something to do with the possibility that the userspace > memory pages could be swapped out in the middle of the DMA) Drivers can choose to support this two different ways. One is to have a buffer of kernel memory mapped into user space and shared with the hardware (this is how OSS did it), the other is to use the 2.6 get_user_pages API to get the physical address of a set of pages and lock them down so they don't wander off during DMA. Both have advantages for different uses. Alan