netdev - Re: [PATCH 1/5] iommu: Replace uses of IOMMU_CAP_CACHE_COHERENCY with dev_is_dma

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Message-ID: <20220406154856.GH2120790@nvidia.com>
Date:   Wed, 6 Apr 2022 12:48:56 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Christian Benvenuti <benve@...co.com>,
        Cornelia Huck <cohuck@...hat.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        iommu@...ts.linux-foundation.org, Jason Wang <jasowang@...hat.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-s390@...r.kernel.org,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Nelson Escobar <neescoba@...co.com>, netdev@...r.kernel.org,
        Rob Clark <robdclark@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        virtualization@...ts.linux-foundation.org,
        Will Deacon <will@...nel.org>,
        "Tian, Kevin" <kevin.tian@...el.com>
Subject: Re: [PATCH 1/5] iommu: Replace uses of IOMMU_CAP_CACHE_COHERENCY
 with dev_is_dma_coherent()

On Wed, Apr 06, 2022 at 05:47:23PM +0200, Christoph Hellwig wrote:
> On Wed, Apr 06, 2022 at 11:14:46AM -0300, Jason Gunthorpe wrote:
> > Really? It is the only condition that dma_info_to_prot() tests to
> > decide of IOMMU_CACHE is used or not, so you are saying that there is
> > a condition where a device can be attached to an iommu_domain and
> > dev_is_dma_coherent() returns the wrong information? How does
> > dma-iommu.c safely use it then?
> 
> arm does not use dma-iommu.c

Oh. I did not know that. Thanks

Jason