linux-kernel - Re: [RFC v2] /dev/iommu uAPI proposal

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Message-ID: <20210804140742.GI1721383@nvidia.com>
Date:   Wed, 4 Aug 2021 11:07:42 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     David Gibson <david@...son.dropbear.id.au>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        "Alex Williamson (alex.williamson@...hat.com)" 
        <alex.williamson@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Jason Wang <jasowang@...hat.com>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shenming Lu <lushenming@...wei.com>,
        Joerg Roedel <joro@...tes.org>,
        Eric Auger <eric.auger@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Robin Murphy <robin.murphy@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        David Woodhouse <dwmw2@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>
Subject: Re: [RFC v2] /dev/iommu uAPI proposal

On Tue, Aug 03, 2021 at 11:58:54AM +1000, David Gibson wrote:
> > I'd rather deduce the endpoint from a collection of devices than the
> > other way around...
> 
> Which I think is confusing, and in any case doesn't cover the case of
> one "device" with multiple endpoints.

Well they are both confusing, and I'd prefer to focus on the common
case without extra mandatory steps. Exposing optional endpoint sharing
information seems more in line with where everything is going than
making endpoint sharing a first class object.

AFAIK a device with multiple endpoints where those endpoints are
shared with other devices doesn't really exist/or is useful? Eg PASID
has multiple RIDs by they are not shared.

Jason