From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from ale.deltatee.com ([207.54.116.67]:46182 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751161AbeC2Ppa (ORCPT ); Thu, 29 Mar 2018 11:45:30 -0400 To: christian.koenig@amd.com, Christoph Hellwig Cc: linaro-mm-sig@lists.linaro.org, amd-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org References: <20180325110000.2238-1-christian.koenig@amd.com> <20180325110000.2238-2-christian.koenig@amd.com> <20180328123830.GB25060@infradead.org> <613a6c91-7e72-5589-77e6-587ec973d553@gmail.com> <5498e9b5-8fe5-8999-a44e-f7dc483bc9ce@amd.com> <16c7bef8-5f03-9e89-1f50-b62fb139a36f@deltatee.com> <6a5c9a10-50fe-b03d-dfc1-791d62d79f8e@amd.com> <73578b4e-664b-141c-3e1f-e1fae1e4db07@amd.com> <1b08c13e-b4a2-08f2-6194-93e6c21b7965@deltatee.com> <70adc2cc-f7aa-d4b9-7d7a-71f3ae99f16c@gmail.com> From: Logan Gunthorpe Message-ID: <98ce6cfd-bcf3-811e-a0f1-757b60da467a@deltatee.com> Date: Thu, 29 Mar 2018 09:45:23 -0600 MIME-Version: 1.0 In-Reply-To: <70adc2cc-f7aa-d4b9-7d7a-71f3ae99f16c@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Subject: Re: [PATCH 2/8] PCI: Add pci_find_common_upstream_dev() Sender: linux-media-owner@vger.kernel.org List-ID: On 29/03/18 05:44 AM, Christian König wrote: > Am 28.03.2018 um 21:53 schrieb Logan Gunthorpe: >> >> On 28/03/18 01:44 PM, Christian König wrote: >>> Well, isn't that exactly what dma_map_resource() is good for? As far as >>> I can see it makes sure IOMMU is aware of the access route and >>> translates a CPU address into a PCI Bus address. >>> I'm using that with the AMD IOMMU driver and at least there it works >>> perfectly fine. >> Yes, it would be nice, but no arch has implemented this yet. We are just >> lucky in the x86 case because that arch is simple and doesn't need to do >> anything for P2P (partially due to the Bus and CPU addresses being the >> same). But in the general case, you can't rely on it. > > Well, that an arch hasn't implemented it doesn't mean that we don't have > the right interface to do it. Yes, but right now we don't have a performant way to check if we are doing P2P or not in the dma_map_X() wrappers. And this is necessary to check if the DMA ops in use support it or not. We can't have the dma_map_X() functions do the wrong thing because they don't support it yet. > Devices integrated in the CPU usually only "claim" to be PCIe devices. > In reality their memory request path go directly through the integrated > north bridge. The reason for this is simple better throughput/latency. These are just more reasons why our patchset restricts to devices behind a switch. And more mess for someone to deal with if they need to relax that restriction. Logan