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 09:58:50 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Christoph Hellwig <hch@....de>
Cc:     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 2019-08-08 1:31 a.m., Christoph Hellwig wrote:
> 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?

Ok, understood. I'll make that change and send some incremental patches
to Bjorn tomorrow.

Logan