Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754521AbYAHRy2 (ORCPT ); Tue, 8 Jan 2008 12:54:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750844AbYAHRyV (ORCPT ); Tue, 8 Jan 2008 12:54:21 -0500 Received: from accolon.hansenpartnership.com ([76.243.235.52]:41670 "EHLO accolon.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750695AbYAHRyU (ORCPT ); Tue, 8 Jan 2008 12:54:20 -0500 Subject: Re: [RFC/PARTIAL PATCH 0/3] dma: passing "attributes" to dma_map_* routines From: James Bottomley To: Roland Dreier Cc: akepner@sgi.com, Tony Luck , Grant Grundler , Jesse Barnes , Jes Sorensen , Randy Dunlap , David Miller , Muli Ben-Yehuda , linux-kernel@vger.kernel.org In-Reply-To: References: <20080108023222.GP23661@sgi.com> <1199809628.3534.34.camel@localhost.localdomain> Content-Type: text/plain Date: Tue, 08 Jan 2008 11:54:13 -0600 Message-Id: <1199814853.3534.39.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.12.2 (2.12.2-2.fc8) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1439 Lines: 30 On Tue, 2008-01-08 at 09:42 -0800, Roland Dreier wrote: > > I'm already on record saying I don't think attributes in the generic > > code is the right approach. All of the attributes I can see adding are > > bus specific (even to the extent that PCIe ones wouldn't apply to PCI > > for instance). > > I think the case before us that Arthur is dealing with is a > counterexample for this: there's nothing bus-specific about it all. > The issue is related to reordering of DMAs within the Altix system > fabric, after they've left the PCI world. This issue would be present > no matter what kind of host bridge you hook up to the system fabric, > be it PCI-X, PCIe, ISA, MCA or whatever. But it is: for performance reasons, the Altix boxes have a rather non standard PCI bridge implementation that gives relaxed ordering on the PCI bus. This behaviour was later standardised to some degree in PCIe, so you could argue they actually have an altix specific PCI bus (PCIa anyone?). Regardless, other manufacturers are probably going to demand something equivalent to this based on the PCIe standard, so we should be ready for it, hence the desire for the bus specific attributes. James -- 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/