linux-kernel - Re: [PATCH v2 04/10] PCI/P2PDMA: Clear ACS P2P flags for all devices behind switches

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Date:   Thu, 1 Mar 2018 16:59:27 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Stephen Bates <sbates@...thlin.com>
Cc:     "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 v2 04/10] PCI/P2PDMA: Clear ACS P2P flags for all devices
 behind switches



On 01/03/18 04:15 PM, Bjorn Helgaas wrote:
> The question is what the relevant switch is.  We call pci_enable_acs()
> on every PCI device, including Root Ports.  It looks like this relies
> on get_upstream_bridge_port() to filter out some things.  I don't
> think get_upstream_bridge_port() is doing the right thing, so we need
> to sort that out first, I guess.

Yes, well if a port has an upstream bridge port and that port has an 
upstream bridge port we are almost certainly looking at a port in a 
switch. If you have a better suggestion to only disable ACS bits on 
downstream switch ports I'd be happy to consider it.


> This might be a good start, but whatever the implications are, they
> need to be distilled and made clear directly in the changelog and the
> Kconfig help text.

Well, I tried. I'll expand on it for v3.

Logan