From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S267436AbTGHPM0 (ORCPT ); Tue, 8 Jul 2003 11:12:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263633AbTGHPLd (ORCPT ); Tue, 8 Jul 2003 11:11:33 -0400 Received: from pc2-cwma1-4-cust86.swan.cable.ntl.com ([213.105.254.86]:26796 "EHLO lxorguk.ukuu.org.uk") by vger.kernel.org with ESMTP id S267364AbTGHPK2 (ORCPT ); Tue, 8 Jul 2003 11:10:28 -0400 Subject: Re: Question regarding DMA xfer to user space directly From: Alan Cox To: Alan Shih Cc: Linux Kernel Mailing List In-Reply-To: References: Content-Type: text/plain Content-Transfer-Encoding: 7bit Organization: Message-Id: <1057677742.4358.36.camel@dhcp22.swansea.linux.org.uk> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.2.2 (1.2.2-5) Date: 08 Jul 2003 16:22:23 +0100 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Maw, 2003-07-08 at 15:50, Alan Shih wrote: > Is there a provision in MM for DMA transfer to user space directly without > allocating a kernel buffer? Yes. Its used both for O_DIRECT I/O (direct to disk I/O from userspace) and for things like tv capture cards. The kernel allows a driver to pin user pages and obtain mappings for them. Note that for large systems user pages may be above the 32bit boundary so you need DAC capable hardware to get the best results