From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from yx-out-2324.google.com (yx-out-2324.google.com [74.125.44.29]) by ozlabs.org (Postfix) with ESMTP id E1433DDDF6 for ; Mon, 27 Apr 2009 20:16:21 +1000 (EST) Received: by yx-out-2324.google.com with SMTP id 8so1260676yxb.39 for ; Mon, 27 Apr 2009 03:16:19 -0700 (PDT) MIME-Version: 1.0 Sender: pku.leo@gmail.com In-Reply-To: References: <20090424183517.GB23140@ovro.caltech.edu> Date: Mon, 27 Apr 2009 18:16:19 +0800 Message-ID: <2a27d3730904270316u6c06eafeja75f6e9e5c83ed29@mail.gmail.com> Subject: Re: [PATCH] fsldma: use PCI Read Multiple command From: Li Yang To: Liu Dave-R63238 Content-Type: text/plain; charset=UTF-8 Cc: linuxppc-dev@ozlabs.org, Dan Williams , linux-kernel@vger.kernel.org, Ira Snyder List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, Apr 27, 2009 at 5:09 PM, Liu Dave-R63238 wrote: >> By default, the Freescale 83xx DMA controller uses the PCI Read Line >> command when reading data over the PCI bus. Setting the >> controller to use the PCI Read Multiple command instead allows the >> controller to read much larger bursts of data, which provides a > drastic >> speed increase. > > IIRC, the default for 83xx DMA controller uses the PCI mem read > command, not mem read line. > > You are assuming the PCI memory space is prefetchable( no side effect) > for DMA. > Is it possible that DMA is from non-prefetchable memory space? I guess it's not reasonable to use DMA from non-prefetchable memory. So it's up to the driver which uses the DMA engine to prevent from using DMA API on non-prefetchable memory. - Leo