Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964837AbWEBO1g (ORCPT ); Tue, 2 May 2006 10:27:36 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964841AbWEBO1f (ORCPT ); Tue, 2 May 2006 10:27:35 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:55507 "EHLO pentafluge.infradead.org") by vger.kernel.org with ESMTP id S964837AbWEBO1f (ORCPT ); Tue, 2 May 2006 10:27:35 -0400 Date: Tue, 2 May 2006 15:27:29 +0100 From: Christoph Hellwig To: Roland Dreier Cc: Christoph Hellwig , Arjan van de Ven , "Bryan O'Sullivan" , openib-general@openib.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 5 of 13] ipath - use proper address translation routine Message-ID: <20060502142729.GA29721@infradead.org> Mail-Followup-To: Christoph Hellwig , Roland Dreier , Arjan van de Ven , Bryan O'Sullivan , openib-general@openib.org, linux-kernel@vger.kernel.org References: <1ab168913f0fea5d18b4.1145913781@eng-12.pathscale.com> <1146509646.20760.63.camel@laptopd505.fenrus.org> <20060502133507.GA26704@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.1i X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1308 Lines: 22 On Tue, May 02, 2006 at 07:24:18AM -0700, Roland Dreier wrote: > Christoph> Or stop doing the dma mapping in the IB upper level > Christoph> drivers. I told you that we'll get broken hardware > Christoph> that doesn't want dma mapping in the upper level > Christoph> driver, and pathscale created exactly that :) > > But see my earlier mail to Arjan about RDMA -- what address can a > protocol (eg SRP initiator) put in a message that the other side will > use to initiate a remote DMA operation? It seems to me it has to be a > bus address, and that means that the protocol has to do the DMA mapping. Then we're back to the discussion on why RDMA is a fundamentally flawed approach, but we already knew that. The usual workaround is to only allow RDMA operations to registered memory windows for which we can use the normal dma operation. There's also the *dac* pci dma operations that can avoid iommu overhead if you support 64bit addressing. But for all this to work dma mapping fundamentally needs to be handled by the low level driver. - 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/