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

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Message-ID: <45A47A71-B435-4DFA-8925-8EB91CEAB230@raithlin.com>
Date:   Wed, 14 Mar 2018 14:05:06 +0000
From:   "Stephen  Bates" <sbates@...thlin.com>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>
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

>I assume you want to exclude Root Ports because of multi-function
>  devices and the "route to self" error.  I was hoping for a reference
>  to that so I could learn more about it.

Apologies Bjorn. This slipped through my net. I will try and get you a reference for RTS in the next couple of days.
    
> While I was looking for it, I found sec 6.12.1.2 (PCIe r4.0), "ACS
> Functions in SR-IOV Capable and Multi-Function Devices", which seems
> relevant.  It talks about "peer-to-peer Requests (between Functions of
> the device)".  Thay says to me that multi-function devices can DMA
> between themselves.
    
I will go take a look. Appreciate the link.

Stephen