From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ovro.ovro.caltech.edu (ovro.ovro.caltech.edu [192.100.16.2]) by ozlabs.org (Postfix) with ESMTP id 6A02ADDE11 for ; Tue, 28 Apr 2009 06:22:50 +1000 (EST) Message-ID: <49F61416.8040501@ovro.caltech.edu> Date: Mon, 27 Apr 2009 13:22:46 -0700 From: David Hawkins MIME-Version: 1.0 To: Timur Tabi Subject: Re: [PATCH] fsldma: use PCI Read Multiple command References: <20090424183517.GB23140@ovro.caltech.edu> <49F608B7.9080409@ovro.caltech.edu> <49F60A3A.4060402@freescale.com> In-Reply-To: <49F60A3A.4060402@freescale.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: linuxppc-dev@ozlabs.org, Dan Williams , Liu Dave-R63238 , 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: , Hi Timur, >> Would you like some sort of summary of this info for a commit >> message? > > That's probably overkill. I just want a sentence or two that tells > someone looking at the code casually that the behavior of reading PCI > memory might be different than what they expect. Could you help us with the wording you'd like to see in the code. Did you want to see something in the header comments, or something near the register settings? How about something like this in place of the existing PCI_RM comment: PRC_RM - PCI read multiple The default PCI read command used by the DMA controller is PCI Read (PCI command 6h). When the burst length is 32-bytes or longer, PCI Read Line (PCI command Eh) is used (undocumented feature of the controller). Using PCI read multiple (PCI command Ch) results in high-performance across PCI bridges. DMA transfers to non-prefetchable PCI registers should not result in prefetched reads, even when using the PCI read multiple command. Cheers, Dave