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Date:   Fri, 31 Aug 2018 09:48:40 -0600
From:   Logan Gunthorpe <>
To:     Christian König <>,,,,,,
Cc:     Stephen Bates <>,
        Christoph Hellwig <>,
        Keith Busch <>,
        Sagi Grimberg <>,
        Bjorn Helgaas <>,
        Jason Gunthorpe <>,
        Max Gurtovoy <>,
        Dan Williams <>,
        Jérôme Glisse <>,
        Benjamin Herrenschmidt <>,
        Alex Williamson <>
Subject: Re: [PATCH v5 01/13] PCI/P2PDMA: Support peer-to-peer memory

On 31/08/18 02:04 AM, Christian König wrote:
> Am 30.08.2018 um 20:53 schrieb Logan Gunthorpe:
>> Some PCI devices may have memory mapped in a BAR space that's
>> intended for use in peer-to-peer transactions. In order to enable
>> such transactions the memory must be registered with ZONE_DEVICE pages
>> so it can be used by DMA interfaces in existing drivers.
> We want to use that feature without ZONE_DEVICE pages for DMA-buf as well.
> How hard would it be to separate enabling P2P detection (e.g. distance 
> between two devices) from this?

Pretty easy. P2P detection is pretty much just pci_p2pdma_distance() ,
which has nothing to do with the ZONE_DEVICE support.

(And the distance function makes use of a number of static functions
which could be combined into a simpler interface, should we need it.)


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