linux-kernel - Re: [PATCH v3 01/11] PCI/P2PDMA: Support peer-to-peer memory

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Message-ID: <3a25744b-daa1-84e3-fbdc-5db2e81d0540@deltatee.com>
Date:   Mon, 26 Mar 2018 09:43:17 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Stephen Bates <sbates@...thlin.com>,
        Bjorn Helgaas <helgaas@...nel.org>
Cc:     Sinan Kaya <okaya@...eaurora.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH v3 01/11] PCI/P2PDMA: Support peer-to-peer memory



On 24/03/18 09:28 AM, Stephen  Bates wrote:
> 1. There is no requirement for a single function to support internal DMAs but in the case of NVMe we do have a protocol specific way for a NVMe function to indicate it supports via the CMB BAR. Other protocols may also have such methods but I am not aware of them at this time.
> 
> 2. For multi-function end-points I think it is a requirement that DMAs *between* functions are supported via an internal path but this can be over-ridden by ACS when supported in the EP.
> 
> 3. For multi-function end-points there is no requirement to support internal DMA within each individual function (i.e. a la point 1 but extended to each function in a MF device). 

Yeah, that make sense. I wasn't making a huge distinction between single
and multi-function devices because from an implementation point of view
it's not that different.

Logan