linux-kernel - Re: [PATCH v3 10/20] iommu: Add set_platform

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Message-ID: <Y4TBng2SY0eGE7wx@nvidia.com>
Date:   Mon, 28 Nov 2022 10:11:42 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Hector Martin <marcan@...can.st>,
        Sven Peter <sven@...npeter.dev>,
        Rob Clark <robdclark@...il.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Yong Wu <yong.wu@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Orson Zhai <orsonzhai@...il.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Thierry Reding <thierry.reding@...il.com>,
        iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 10/20] iommu: Add set_platform_dma iommu ops

On Mon, Nov 28, 2022 at 02:46:38PM +0800, Lu Baolu wrote:
> When VFIO finishes assigning a device to user space and calls
> iommu_group_release_dma_owner() to return the device to kernel, the IOMMU
> core will attach the default domain to the device. Unfortunately, some
> IOMMU drivers don't support default domain, hence in the end, the core
> calls .detach_dev instead.
> 
> This adds set_platform_dma iommu ops to make it clear that what it does
> is returning control back to the platform DMA ops.
> 
> Suggested-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  include/linux/iommu.h | 4 ++++
>  1 file changed, 4 insertions(+)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

> + * @set_platform_dma: Returning control back to the platform DMA ops. Only
> + *                    valid for IOMMU drivers which don't support default
> + *                    domain.

I would add:

  This op is to support old IOMMU drivers, new drivers should use
  default domains, and the common IOMMU DMA ops.

Jason