Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757636AbYLDCoT (ORCPT ); Wed, 3 Dec 2008 21:44:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751666AbYLDCoG (ORCPT ); Wed, 3 Dec 2008 21:44:06 -0500 Received: from an-out-0708.google.com ([209.85.132.242]:38479 "EHLO an-out-0708.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751063AbYLDCoE (ORCPT ); Wed, 3 Dec 2008 21:44:04 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version :content-type:content-transfer-encoding:content-disposition :references; b=EhWe9Uanmo92cFRO0wu3tRAS5AbcHcaWq+ZDWqGhiQIX9SWnBcvXVe/y9/A8XToxUy mxaytQv2RzWa0m+Vsnm4855+/Y8u6wp9cfcs353fxbXpqGv4Oi4TcVq1mm68YO9I1Hr/ 118IWAAr1wqtPtQUtMb6HciPSdEeWLpv5sV8c= Message-ID: <208aa0f00812031844u779584e8q633a5f1b92a97426@mail.gmail.com> Date: Wed, 3 Dec 2008 18:44:01 -0800 From: "Edward Estabrook" To: "Leon Woestenberg" Subject: Re: [PATCH 1/1] Userspace I/O (UIO): Add support for userspace DMA Cc: edward_estabrook@agilent.com, linux-kernel@vger.kernel.org, hjk@linutronix.de, gregkh@suse.de, edward.estabrook@gmail.com In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <43FC624C55D8C746A914570B66D642610367F29B@cos-us-mb03.cos.agilent.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 917 Lines: 20 > You are using a magic value to mmap(), just to keep options open: > > Would this in the future allow us to also add support for streaming > non-coherent DMA directly into user space buffers? Yes, but additional userspace control is also required. Specifically: 1) The specification of direction at the time of buffer creation, unless force DMA_BIDIRECTIONAL is assumed. 2) An API to faciliate userspace control over dma_unmap_page() / dma_sync_single_for_cpu() calls (perhaps by further overloading of the write method). The use of this magic value does not prevent the future addition of streaming DMA support, but does not provide sufficient controls. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/