From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=wmYC=LT=vger.kernel.org=linux-kernel-owner@kernel.org>
X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on
	aws-us-west-2-korg-lkml-1.web.codeaurora.org
X-Spam-Level: 
X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,
	MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no
	version=3.4.0
Received: from mail.kernel.org (mail.kernel.org [198.145.29.99])
	by smtp.lore.kernel.org (Postfix) with ESMTP id 7C868C433F5
	for <linux-kernel@archiver.kernel.org>; Wed,  5 Sep 2018 19:19:17 +0000 (UTC)
Received: from vger.kernel.org (vger.kernel.org [209.132.180.67])
	by mail.kernel.org (Postfix) with ESMTP id 2F25220839
	for <linux-kernel@archiver.kernel.org>; Wed,  5 Sep 2018 19:19:17 +0000 (UTC)
DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2F25220839
Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de
Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1727790AbeIEXus (ORCPT
        <rfc822;linux-kernel@archiver.kernel.org>);
        Wed, 5 Sep 2018 19:50:48 -0400
Received: from verein.lst.de ([213.95.11.211]:46885 "EHLO newverein.lst.de"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1726544AbeIEXus (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 5 Sep 2018 19:50:48 -0400
Received: by newverein.lst.de (Postfix, from userid 2407)
        id CA17368D40; Wed,  5 Sep 2018 21:22:52 +0200 (CEST)
Date:   Wed, 5 Sep 2018 21:22:52 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Logan Gunthorpe <logang@deltatee.com>
Cc:     Jason Gunthorpe <jgg@mellanox.com>, linux-kernel@vger.kernel.org,
        linux-pci@vger.kernel.org, linux-nvme@lists.infradead.org,
        linux-rdma@vger.kernel.org, linux-nvdimm@lists.01.org,
        linux-block@vger.kernel.org, Stephen Bates <sbates@raithlin.com>,
        Christoph Hellwig <hch@lst.de>,
        Keith Busch <keith.busch@intel.com>,
        Sagi Grimberg <sagi@grimberg.me>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Max Gurtovoy <maxg@mellanox.com>,
        Dan Williams <dan.j.williams@intel.com>,
        =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Alex Williamson <alex.williamson@redhat.com>,
        Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>
Subject: Re: [PATCH v5 10/13] nvme-pci: Add support for P2P memory in
 requests
Message-ID: <20180905192252.GA888@lst.de>
References: <20180830185352.3369-1-logang@deltatee.com> <20180830185352.3369-11-logang@deltatee.com> <20180904151638.GL335@mellanox.com> <d5548f5d-59df-f38e-255d-59b46a17a219@deltatee.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <d5548f5d-59df-f38e-255d-59b46a17a219@deltatee.com>
User-Agent: Mutt/1.5.17 (2007-11-01)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Sep 04, 2018 at 09:47:07AM -0600, Logan Gunthorpe wrote:
> 
> 
> On 04/09/18 09:16 AM, Jason Gunthorpe wrote:
> >>  	if (iod->nents) {
> >> -		dma_unmap_sg(dev->dev, iod->sg, iod->nents, dma_dir);
> >> +		/* P2PDMA requests do not need to be unmapped */
> >> +		if (!is_pci_p2pdma_page(sg_page(iod->sg)))
> >> +			dma_unmap_sg(dev->dev, iod->sg, iod->nents, dma_dir);
> > 
> > This seems like a poor direction, if we add IOMMU hairpin support we
> > will need unmapping.
> 
> It can always be added later. In any case, you'll have to convince
> Christoph who requested the change; I'm not that invested in this decision.

Yes, no point to add dead code here.  In the long run we should
aim for hiding the p2p address translation behind the normal DMA API
anyway, but we're not quite ready for it yet.