From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751876AbdJWWEj (ORCPT ); Mon, 23 Oct 2017 18:04:39 -0400 Received: from ale.deltatee.com ([207.54.116.67]:52858 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751113AbdJWWEe (ORCPT ); Mon, 23 Oct 2017 18:04:34 -0400 To: David Laight , "'Petrosyan, Ludwig'" Cc: "Deucher, Alexander" , "linux-kernel@vger.kernel.org" , "linux-rdma@vger.kernel.org" , "linux-nvdimm@lists.01.org" , "Linux-media@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , "linux-pci@vger.kernel.org" , "Bridgman, John" , "Kuehling, Felix" , "Sagalovitch, Serguei" , "Blinzer, Paul" , "Koenig, Christian" , "Suthikulpanit, Suravee" , "Sander, Ben" References: <7f5e0303-f4ea-781a-8dec-74b30990d54f@desy.de> <1381807327.12461494.1508652825239.JavaMail.zimbra@desy.de> <063D6719AE5E284EB5DD2968C1650D6DD00A04EA@AcuExch.aculab.com> From: Logan Gunthorpe Message-ID: Date: Mon, 23 Oct 2017 16:04:26 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6DD00A04EA@AcuExch.aculab.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.162 X-SA-Exim-Rcpt-To: ben.sander@amd.com, Suravee.Suthikulpanit@amd.com, Christian.Koenig@amd.com, Paul.Blinzer@amd.com, Serguei.Sagalovitch@amd.com, Felix.Kuehling@amd.com, John.Bridgman@amd.com, linux-pci@vger.kernel.org, dri-devel@lists.freedesktop.org, Linux-media@vger.kernel.org, linux-nvdimm@lists.01.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, Alexander.Deucher@amd.com, ludwig.petrosyan@desy.de, David.Laight@ACULAB.COM X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: Enabling peer to peer device transactions for PCIe devices X-SA-Exim-Version: 4.2.1 (built Tue, 02 Aug 2016 21:08:31 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 23/10/17 10:08 AM, David Laight wrote: > It is also worth checking that the hardware actually supports p2p transfers. > Writes are more likely to be supported then reads. > ISTR that some intel cpus support some p2p writes, but there could easily > be errata against them. Ludwig mentioned a PCIe switch. The few switches I'm aware of support P2P transfers. So if everything is setup correctly, the TLPs shouldn't even touch the CPU. But, yes, generally it's a good idea to start with writes and see if they work first. Logan