linux-kernel - Re: [PATCH v1 5/8] iommu/amd: Use iommu_attach/detach

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Date:   Mon, 14 Feb 2022 11:00:59 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Will Deacon <will@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>, rafael@...nel.org,
        Diana Craciun <diana.craciun@....nxp.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Stuart Yoder <stuyoder@...il.com>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Li Yang <leoyang.li@....com>,
        Dmitry Osipenko <digetx@...il.com>,
        iommu@...ts.linux-foundation.org, linux-pci@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 5/8] iommu/amd: Use iommu_attach/detach_device()

On Mon, Feb 14, 2022 at 03:23:07PM +0100, Joerg Roedel wrote:

> Device drivers calling into iommu_attach_device() is seldom a good
> idea.  In this case the sound device has some generic hardware
> interface so that an existing sound driver can be re-used. Making this
> driver call iommu-specific functions for some devices is something hard
> to justify.

Er, so this is transparent to the generic sound device? I guess
something fixed up the dma_api on that device to keep working?

But, then, the requirement is that nobody is using the dma API when we
make this change?

> With sub-groups on the other hand it would be a no-brainer, because the
> sound device would be in a separate sub-group. Basically any device in
> the same group as the GPU would be in a separate sub-group.

I don't think it matters how big/small the group is, only that when we
change the domain we know everything flowing through the domain is
still happy.

Jason