linux-kernel - Re: [PATCH v2 03/14] PCI/P2PDMA: Add constants for not-supported result upstream_bridge

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Date:   Thu, 8 Aug 2019 09:31:09 +0200
From:   Christoph Hellwig <hch@....de>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-rdma@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        Christian Koenig <Christian.Koenig@....com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>,
        Dan Williams <dan.j.williams@...el.com>,
        Eric Pilmore <epilmore@...aio.com>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [PATCH v2 03/14] PCI/P2PDMA: Add constants for not-supported
 result upstream_bridge_distance()

On Wed, Aug 07, 2019 at 09:58:06AM -0600, Logan Gunthorpe wrote:
> We only calculate it at the same time as we calculate the distance. This
> is necessary because, to calculate the type, we have to walk the tree
> and check the ACS bits. If we separated it, we'd have to walk the tree
> twice in a very similar way just to determine both the distance and the
> mapping type.

Calculating it together makes perfect sense.  What I find odd is the
overloading of a single return value.  Why not return the map type as
the return value, and the distance as a by reference argument to keep
them properly separated?