From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752399AbeCZPqv (ORCPT ); Mon, 26 Mar 2018 11:46:51 -0400 Received: from ale.deltatee.com ([207.54.116.67]:58706 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751907AbeCZPqt (ORCPT ); Mon, 26 Mar 2018 11:46:49 -0400 To: Bjorn Helgaas , Jonathan Cameron Cc: Sinan Kaya , 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 , Christoph Hellwig , Jens Axboe , Keith Busch , Sagi Grimberg , Bjorn Helgaas , Jason Gunthorpe , Max Gurtovoy , Dan Williams , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Benjamin Herrenschmidt , Alex Williamson , Eric Wehage References: <20180312193525.2855-1-logang@deltatee.com> <20180312193525.2855-2-logang@deltatee.com> <59fd2f5d-177f-334a-a9c4-0f8a6ec7c303@codeaurora.org> <24d8e5c2-065d-8bde-3f5d-7f158be9c578@deltatee.com> <20180326121138.00005e30@huawei.com> <20180326140118.GA221690@bhelgaas-glaptop.roam.corp.google.com> From: Logan Gunthorpe Message-ID: Date: Mon, 26 Mar 2018 09:46:24 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180326140118.GA221690@bhelgaas-glaptop.roam.corp.google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.162 X-SA-Exim-Rcpt-To: Eric.Wehage@huawei.com, alex.williamson@redhat.com, benh@kernel.crashing.org, jglisse@redhat.com, dan.j.williams@intel.com, maxg@mellanox.com, jgg@mellanox.com, bhelgaas@google.com, sagi@grimberg.me, keith.busch@intel.com, axboe@kernel.dk, hch@lst.de, sbates@raithlin.com, linux-block@vger.kernel.org, linux-nvdimm@lists.01.org, linux-rdma@vger.kernel.org, linux-nvme@lists.infradead.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, okaya@codeaurora.org, Jonathan.Cameron@huawei.com, helgaas@kernel.org X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH v3 01/11] PCI/P2PDMA: Support peer-to-peer memory 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 26/03/18 08:01 AM, Bjorn Helgaas wrote: > On Mon, Mar 26, 2018 at 12:11:38PM +0100, Jonathan Cameron wrote: >> On Tue, 13 Mar 2018 10:43:55 -0600 >> Logan Gunthorpe wrote: >>> It turns out that root ports that support P2P are far less common than >>> anyone thought. So it will likely have to be a white list. >> >> This came as a bit of a surprise to our PCIe architect. >> >> His follow up was whether it was worth raising an ECR for the PCIe spec >> to add a capability bit to allow this to be discovered. This might >> long term avoid the need to maintain the white list for new devices. >> >> So is it worth having a long term solution for making this discoverable? > > It was surprising to me that there's no architected way to discover > this. It seems like such an obvious thing that I guess I assumed the > omission was intentional, i.e., maybe there's something that makes it > impractical, but it would be worth at least asking somebody in the > SIG. It seems like for root ports in the same root complex, at least, > there could be a bit somewhere in the root port or the RCRB (which > Linux doesn't support yet). Yes, I agree. It would be a good long term solution to have this bit in the spec. That would avoid us needing to create a white list for new hardware. However, I expect it would be years before we can rely on it so someone may yet implement that white list. Logan