From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758660AbYEGOWn (ORCPT ); Wed, 7 May 2008 10:22:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755868AbYEGOWc (ORCPT ); Wed, 7 May 2008 10:22:32 -0400 Received: from de01egw02.freescale.net ([192.88.165.103]:48181 "EHLO de01egw02.freescale.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755674AbYEGOWa (ORCPT ); Wed, 7 May 2008 10:22:30 -0400 Message-ID: <4821BB0E.80000@freescale.com> Date: Wed, 07 May 2008 09:22:06 -0500 From: Timur Tabi User-Agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv:1.8.1.13) Gecko/20080313 SeaMonkey/1.1.9 MIME-Version: 1.0 To: Takashi Iwai CC: benh@kernel.crashing.org, alsa-devel@alsa-project.org, linuxppc-dev list , Linux Kernel list Subject: Re: ALSA vs. non coherent DMA References: <1210032508.21644.129.camel@pasglop> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Takashi Iwai wrote: > This is a mmap of the data record to be shared in realtime with apps. > The app updates its data pointer (appl_ptr) on the mmapped buffer > while the driver updates the data (e.g. DMA position, called hwptr) on > the fly on the mmapped record. Due to its real-time nature, it has to > be coherent -- at least, it was a problem on ARM. This doesn't sound like a coherency problem to me, and least not one you'd find on PowerPC. Both the driver and the application run on the host CPU, so there shouldn't be any coherency problem. My understanding is that a "non coherent" platform is one where the host CPU isn't aware when a *hardware device* writes directly to memory, e.g. via DMA. -- Timur Tabi Linux kernel developer at Freescale