linux-kernel - Re: [RFC PATCH 00/28] Removing struct page from P2PDMA

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Message-ID: <20190624185444.GD8268@ziepe.ca>
Date:   Mon, 24 Jun 2019 15:54:44 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-block@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-pci@...r.kernel.org, linux-rdma <linux-rdma@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Keith Busch <kbusch@...nel.org>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [RFC PATCH 00/28] Removing struct page from P2PDMA

On Mon, Jun 24, 2019 at 12:28:33PM -0600, Logan Gunthorpe wrote:

> > Sounded like this series does generate the dma_addr for the correct
> > device..
> 
> This series doesn't generate any DMA addresses with dma_map(). The
> current p2pdma code ensures everything is behind the same root port and
> only uses the pci bus address. This is valid and correct, but yes it's
> something to expand upon.

I think if you do this it still has to be presented as the same API
like dma_map that takes in the target device * and produces the device
specific dma_addr_t

Otherwise this whole thing is confusing and looks like *all* of it can
only work under the switch assumption

Jason